LAYERED REACTIVE ELEMENTS IN A THERMO-ELECTROCHEMICAL REACTOR FOR HYDROGEN AND CARBON MONOXIDE PRODUCTION AND METHOD FOR USING THE SAME

Abstract

A method and reactor for a hybrid thermo-electrochemical cycle using a layered reactive element is disclosed. The method includes heating the reactive element with a heat source, the reactive element having a metal oxide core that is redox-active, an outer layer, and an ion conductor layer between the core and the outer layer. The method includes increasing a chemical potential of oxygen in the core, driving O2− ions out as O2, the chemical potential increased through applying a first bias voltage between the core and the outer layer. The method includes exposing the reactive element to an input gas, and decreasing the chemical potential of oxygen in the core, driving oxygen from the input gas into the core leaving a gas product, the chemical potential decreased through applying a second bias voltage between the core and the outer layer. The first and second bias voltages have opposite polarity.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application 63/518,553, filed Aug. 9, 2023 titled “Thermo-Electrochemical Reactor for Hydrogen and Carbon Monoxide Production and Methods for the Same,” the entirety of the disclosure of which is hereby incorporated by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under DE-EE0010243 and DE-EE0008991, awarded by the Department of Energy. The government has certain rights in the invention.

TECHNICAL FIELD

Aspects of this document relate generally to thermo-electrochemical reactors.

BACKGROUND

Hydrogen is a clean fuel with high energy content and environmentally friendly combustion products. However, conventional hydrogen production often relies on fossil fuels, undermining its environmental benefits. Solar Thermochemical Hydrogen (STCH) production addresses this issue by using the sun's energy to drive thermochemical reactions that split water produce hydrogen. This method offers a sustainable, greenhouse gas-free way to produce hydrogen for use in various sectors, including transportation and electricity generation.

These reactions can also be used to split carbon dioxide to produce carbon monoxide, which has numerous applications. Combined with efforts to capture carbon dioxide from industrial processes as well as the atmosphere, these reactions can provide a sustainable and economically attractive pathway to producing a useful feedstock such as carbon monoxide, while also having a positive impact on the environment.

Some of the best STCH technology makes use of redox-active metal oxides, or MO_x. The current state-of-the-art MO_x materials is CeO₂. FIG. 1 illustrates a basic two-step CeO₂ thermochemical (hereinafter TC) cycle that operates at equilibrium. The cycle is being shown in thermal reduction-temperature (δ-T) space, with the thermal reduction reaction in grey and the water splitting reaction in black.

Materials constraints pit the theoretical efficiency of this two-step MO_x cycle against chemical equilibrium and kinetics. On the one hand, to spontaneously reduce steam (i.e., the water splitting step in FIG. 1) in the presence of substantial concentrations of the H₂ product (i.e., to achieve practically relevant reaction yields and related acceptable cycle times (τ) no longer than several minutes), the MO_x reduction enthalpy must substantially exceed that of steam (ΔH_H2O(g)≈250 KJ/mol O). For ceria (CeO₂), this reaction exotherm is ΔQ_CeO2=ΔH_CeO2−ΔH_H2O(g)≈200 KJ/mol O.

On the other hand, comparatively high ΔH_MOx limits the cycle's theoretical efficiency η=ΔG_H2O/ΔH_MOx, and the MO_x extent of thermal reduction (δ_R) at practical temperatures (e.g., ˜1500° C.). The reversible oxygen capacity Δδ=δ_R−δ_OX, where dox is the MO_x extent of re-oxidation, is then also limited (e.g., Δδ˜0.03−0.04 for ceria as shown in FIG. 1).

Extensive MO_x research has shown that lowering ΔH to increase δ_R and η inevitably results in lower yields and slower kinetics. This leads to increased MO_x inventories, a primary cost driver, with questionable practical gains. Despite all efforts, ceria persists as the state-of-the-art MO_x.

The practical implementation of the TC cycle within a reactor is also faced with constraints and tradeoffs that are equally persistent. Two-step MO_x cycles are theoretically the most efficient, but practical implementation has been challenging. Multi-step hybrid cycles can ease material and temperature constraints, but they also add losses and process complexity through their multiple conversion steps. The hybrid sulfur cycle, which is nominally two-step but not MO_x, also has complexity challenges. High-pressure, high-temperature, and high-concentration sulfuric acid electrolysis, and SO₂/O₂ separation. Lowering temperatures has diminishing returns, as it can decrease the fraction of thermal work at the expense of increased electrical input.

Producing fuels and chemicals from solar (or more generally, renewable) energy is challenging because of its intermittent and seasonal nature. Solar energy is variable in both availability and cost, with modest time windows of low-cost energy availability. Absent a substantial amount of thermal and/or battery energy storage (adding to the energy cost), energy price variability may make H₂ production advantageous for a capacity factor potentially as low as ˜20-30%.

In order to meet cost targets that would make STCH (and any other scalable renewable hydrogen production approach) economically viable, it must meet a criteria trifecta: (1) low capital cost, (2) low energy use per unit H₂ or CO product (i.e., high efficiency), and (3) nimble response to (low) energy prices and resource availability. Put differently, a successful H₂ production technology should be low capital cost so that it may be both oversized and economically operated for a fraction of the time, be able to quickly ramp, and be efficient, so that it may produce large amounts of H₂ during comparatively brief operating times.

It is important to appreciate that meeting two of the three criteria is not sufficient. In an example where (1) and (2) are met, a slow-response technology would not be able to ramp up/down advantageously in response to favorable energy prices and resource availability. If (2) and (3) are met, a high capital cost would necessitate a high capacity factor, without opportunity to operate intermittently (e.g., only at times of minimal energy cost).

SUMMARY

According to one aspect, a thermo-electrochemical reactor includes at least one layered reactive element, each layered reactive element having a metal oxide core that is redox-active and is a mixed ionic-electronic conductor (MIEC), an outer layer that is also an MIEC, an ion conductor layer between the metal oxide core and the outer layer, a TEC reduction mode, and a TEC oxidation mode. The reactor also includes a controller communicatively coupled to the metal oxide core and the outer layer of each of the at least one layered reactive element. The reactor also includes a heat source. For each layered reactive element, the TEC reduction mode includes the metal oxide core having an increased chemical potential of oxygen relative to a gas phase that drives O²⁻ ions out of the metal oxide core, through the ion conductor layer and the outer layer and into the gas phase as O₂, with the chemical potential of oxygen in the metal oxide core being increased relative to the gas phase through applying a first bias voltage between the metal oxide core and the outer layer. For each layered reactive element, the TEC oxidation mode includes the metal oxide core having a decreased chemical potential of oxygen relative to the gas phase that drives one of oxygen from steam and oxygen from carbon dioxide back into the metal oxide core, through the ion conductor layer and the outer layer, leaving a gas product that is one of H₂ in the gas phase and CO in the gas phase, with the chemical potential of oxygen in the metal oxide core being decreased relative to the gas phase through applying a second bias voltage between the metal oxide core and the outer layer. The controller is configured to drive the thermo-electrochemical reactor to carry out a TEC cycle by alternating between applying the first bias voltage and applying the second bias voltage to at least one layered reactive element while the at least one layered reactive element is being heated by the heat source, cycling the at least one layered reactive element between the TEC reduction mode and the TEC oxidation mode. The first bias voltage and the second bias voltage have opposite polarity.

Particular embodiments may comprise one or more of the following features. The at least one layered reactive element may be hollow. each layered reactive element of the at least one layered reactive element may include two metal oxide cores, two ion conductor layers, and two outer layers. The layered reactive element may be substantially planar. The metal oxide core may include a perovskite. The metal oxide core may include CAM28. The outer layer may be gadolinium-doped ceria (GDC). The ion conductor layer may be yttria-stabilized zirconia. The thermo-electrochemical reactor may include a plurality of layered reactive elements. At least one layered reactive element of the plurality of layered reactive elements may be in the TEC oxidation mode while at least a different layered reactive element of the plurality of layered reactive elements is in the TEC reduction mode. The plurality of layered reactive elements may move throughout the thermo-electrochemical reactor as the controller drives the thermo-electrochemical reactor to carry out the TEC cycle. The thermo-electrochemical reactor may further include an insulated housing, a gas inlet, and/or a gas outlet. The at least one layered reactive element may remain motionless with respect to the insulated housing as the controller cycles the at least one layered reactive element between the TEC oxidation mode and the TEC reduction mode. The heat source may be solar-based. The controller may be further configured displace the gas product with a sweep gas, the displaced gas product extracted through a gas outlet. The sweep gas may be steam.

According to another aspect of the disclosure, a method for carrying out a hybrid thermo-electrochemical cycle using a layered reactive element includes heating the layered reactive element with a heat source, the layered reactive element having a metal oxide core that is redox-active and is a mixed ionic-electronic conductor (MIEC), an outer layer that is also an MIEC, and an ion conductor layer between the metal oxide core and the outer layer. The method includes increasing a chemical potential of oxygen in the metal oxide core, relative to a gas phase, thereby driving O²⁻ ions out of the metal oxide core, through the ion conductor layer and the outer layer and into the gas phase as O₂, the chemical potential of oxygen in the metal oxide core being increased relative to the gas phase through applying a first bias voltage between the metal oxide core and the outer layer. The method includes exposing the layered reactive element to an input gas, the input gas displacing the O₂ in the gas phase, and then decreasing the chemical potential of oxygen in the metal oxide core, relative to the gas phase, thereby driving oxygen from the input gas into the metal oxide core, through the ion conductor layer and the outer layer, leaving a gas product in the gas phase, with the chemical potential of oxygen in the metal oxide core being decreased relative to the gas phase through applying a second bias voltage between the metal oxide core and the outer layer. The method includes extracting the gas product by displacing the gas product with a sweep gas. The first bias voltage and the second bias voltage have opposite polarity.

Particular embodiments may comprise one or more of the following features. The sweep gas may be steam. The input gas may be one of steam and carbon dioxide, and the gas product may be one of H₂ and CO. The metal oxide core may include a perovskite. The metal oxide core may include CAM28. The outer layer may be gadolinium-doped ceria (GDC). The ion conductor layer may be yttria-stabilized zirconia.

Aspects and applications of the disclosure presented here are described below in the drawings and detailed description. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts. The inventors are fully aware that they can be their own lexicographers if desired. The inventors expressly elect, as their own lexicographers, to use only the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise and then further, expressly set forth the “special” definition of that term and explain how it differs from the plain and ordinary meaning. Absent such clear statements of intent to apply a “special” definition, it is the inventors' intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims.

The inventors are also aware of the normal precepts of English grammar. Thus, if a noun, term, or phrase is intended to be further characterized, specified, or narrowed in some way, then such noun, term, or phrase will expressly include additional adjectives, descriptive terms, or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms, or modifiers, it is the intent that such nouns, terms, or phrases be given their plain, and ordinary English meaning to those skilled in the applicable arts as set forth above.

Further, the inventors are fully informed of the standards and application of the special provisions of 35 U.S.C. § 112 (f). Thus, the use of the words “function,” “means” or “step” in the Detailed Description or Description of the Drawings or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. § 112 (f), to define the invention. To the contrary, if the provisions of 35 U.S.C. § 112 (f) are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for”, and will also recite the word “function” (i.e., will state “means for performing the function of [insert function]”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for performing the function of . . . ” or “step for performing the function of . . . ,” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventors not to invoke the provisions of 35 U.S.C. § 112 (f). Moreover, even if the provisions of 35 U.S.C. § 112 (f) are invoked to define the claimed aspects, it is intended that these aspects not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the disclosure, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function.

The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and:

FIG. 1 shows a basic two-step CeO2 thermochemical cycle;

FIG. 2 shows a schematic view of a two-step thermo-electrochemical (TEC) cycle and a layered reactive element;

FIG. 3 shows an equilibrium TEC cycle in δ-V space;

FIGS. 4A, 4B, and 4C show planar, tubular, and button-style layered reactive elements, respectively;

FIGS. 5A and 5B show different embodiments of a thermo-electrochemical reactor; and

FIG. 6 is a process flow of a method for carrying out a hybrid thermo-electrochemical cycle using a layered reactive element.

DETAILED DESCRIPTION

This disclosure, its aspects and implementations, are not limited to the specific material types, components, methods, or other examples disclosed herein. Many additional material types, components, methods, and procedures known in the art are contemplated for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any components, models, types, materials, versions, quantities, and/or the like as is known in the art for such systems and implementing components, consistent with the intended operation.

The word “exemplary,” “example,” or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It is to be appreciated that a myriad of additional or alternate examples of varying scope could have been presented, but have been omitted for purposes of brevity.

While this disclosure includes a number of embodiments in many different forms, there is shown in the drawings and will herein be described in detail particular embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the disclosed methods and systems, and is not intended to limit the broad aspect of the disclosed concepts to the embodiments illustrated.

Hydrogen is a clean fuel with high energy content and environmentally friendly combustion products. However, conventional hydrogen production often relies on fossil fuels, undermining its environmental benefits. Solar Thermochemical Hydrogen (STCH) production addresses this issue by using the sun's energy to drive thermochemical reactions that split water produce hydrogen. This method offers a sustainable, greenhouse gas-free way to produce hydrogen for use in various sectors, including transportation and electricity generation.

These reactions can also be used to split carbon dioxide to produce carbon monoxide, which has numerous applications. Combined with efforts to capture carbon dioxide from industrial processes as well as the atmosphere, these reactions can provide a sustainable and economically attractive pathway to producing a useful feedstock such as carbon monoxide, while also having a positive impact on the environment.

Some of the best STCH technology makes use of redox-active metal oxides, or MO_x. The current state-of-the-art MO_x materials is CeO₂. FIG. 1 illustrates a basic two-step CeO₂ thermochemical (hereinafter TC) cycle that operates at equilibrium. The cycle is being shown in thermal reduction-temperature (8-T) space, with the thermal reduction reaction in grey and the water splitting reaction in black.

Materials constraints pit the theoretical efficiency of this two-step MO_x cycle against chemical equilibrium and kinetics. On the one hand, to spontaneously reduce steam (i.e., the water splitting step in FIG. 1) in the presence of substantial concentrations of the H₂ product (i.e., to achieve practically relevant reaction yields and related acceptable cycle times (t) no longer than several minutes), the MO_x reduction enthalpy must substantially exceed that of steam (ΔH_H2O(g)≈250 KJ/mol O). For ceria (CeO₂), this reaction exotherm is ΔQ_CeO2=ΔH_CeO2−ΔH_H2O(g)≈200 KJ/mol O.

On the other hand, comparatively high ΔH_MOx limits the cycle's theoretical efficiency η=ΔG_H2O/ΔH_MOx, and the MO_x extent of thermal reduction (δ_R) at practical temperatures (e.g., ˜1500° C.). The reversible oxygen capacity Δδ=δ_R−δ_OX, where dox is the MO_x extent of re-oxidation, is then also limited (e.g., Δδ˜0.03−0.04 for ceria as shown in FIG. 1).

Extensive MO_x research has shown that lowering ΔH to increase δ_R and η inevitably results in lower yields and slower kinetics. This leads to increased MO_x inventories, a primary cost driver, with questionable practical gains. Despite all efforts, ceria persists as the state-of-the-art MO_x.

The practical implementation of the TC cycle within a reactor is also faced with constraints and tradeoffs that are equally persistent. Two-step MO_x cycles are theoretically the most efficient, but practical implementation has been challenging. Multi-step hybrid cycles can ease material and temperature constraints, but they also add losses and process complexity through their multiple conversion steps. The hybrid sulfur cycle, which is nominally two-step but not MO_x, also has complexity challenges. High-pressure, high-temperature, and high-concentration sulfuric acid electrolysis, and SO₂/O₂ separation. Lowering temperatures has diminishing returns, as it can decrease the fraction of thermal work at the expense of increased electrical input.

Producing fuels and chemicals from solar (or more generally, renewable) energy is challenging because of its intermittent and seasonal nature. Solar energy is variable in both availability and cost, with modest time windows of low-cost energy availability. Absent a substantial amount of thermal and/or battery energy storage (adding to the energy cost), energy price variability may make H₂ production advantageous for a capacity factor potentially as low as ˜20-30%.

In order to meet cost targets that would make STCH (and any other scalable renewable hydrogen production approach) economically viable, it must meet a criteria trifecta: (1) low capital cost, (2) low energy use per unit H₂ or CO product (i.e., high efficiency), and (3) nimble response to (low) energy prices and resource availability. Put differently, a successful H₂ production technology should be low-cost so that it may be both oversized and economically operated for a fraction of the time, be able to quickly ramp, and be efficient, so that it may produce large amounts of H₂ during comparatively brief operating times.

It is important to appreciate that meeting two of the three criteria is not sufficient. In an example where (1) and (2) are met, a slow-response technology would not be able to ramp up/down advantageously in response to favorable energy prices and resource availability. If (2) and (3) are met, a high capital cost would necessitate a high capacity factor, without opportunity to operate intermittently (e.g., only at times of minimal energy cost).

Contemplated herein is a two-step thermo-electrochemical reactor (hereinafter “TEC reactor”) that uses a hybrid cycle for solar H₂ or CO production. According to various embodiments, the contemplated reactor uses a hybrid thermochemical and electrochemical cycle to produce hydrogen from steam and carbon monoxide from CO2 at high temperatures. Specifically, the contemplated method augments the well-known MO_x thermochemical cycle with an alternating electrochemical potential (V). These thermochemical cycle reactions are also driven by renewable solar heat harnessed by the contemplated TEC reactor, according to various embodiments. Advantageously, the contemplated TEC reactor and method are able to form the H₂ and CO at lower temperatures, with higher efficiency and faster start/stop times. This results in an overall lower capital and operating cost than closely related conventional processes, according to various embodiments.

According to various embodiments, the contemplated TEC reactor uses a hybrid cycle that augments the “basic” two-step redox-active MO_x thermochemical cycle, addressing its drawbacks while preserving the advantages. The TEC hybrid cycle contemplated herein adds an alternating electrochemical potential (i.e., a bias voltage V) to assist both steps of the “basic” thermochemical cycle, the thermal reduction (TR) step and the water splitting (WS) or re-oxidation step. The number of steps in the cycle remains the same, preserving the simplicity of two-step MO_x cycles. According to various embodiments, the bias voltage enables thermal reduction at a lower temperature than otherwise possible, and deeper reoxidation than otherwise possible, for an overall more productive and more efficient cycle.

Although hybrid two-step MO_x cycles have been understood as advantageous and theorized for over a decade, a practical implementation has remained elusive. The contemplated TEC reactor solves this problem by replacing the “bare” MO_x from the basic TC cycle with novel layered reactive elements that enable hybridization with electrical input. According to various embodiments, the layered reactive elements comprise an inner mixed ionic-electronic conductor (MIEC) MO_x core, a thin but dense ion conductor layer, and an outer porous electrode and current collector.

The contemplated TEC reactor and method for operating the same offers advantages that overcome some of the most intractable basic two-step STCH challenges. The contemplated reactor and method enables the use of previously ignored MO_x materials by broadening the MO_x properties space. The contemplated reactor has a tunable cycle temperature which can be dialed in to be compatible with direct heat input from current and prospective concentrating solar technologies. The contemplated reactor and method offers significantly lower energy use per H₂ product, as well as significantly lower capital and operating costs. The reactor and method contemplated herein may also yield a lower levelized H₂ cost (LCOH₂), with a path toward $1/kg H₂.

It should be noted that while much of the discussion is done in the context of water splitting to yield H₂ and the overcoming of the challenges of practical implementation of STCH, the contemplated TEC reactor and associated method is not limited to water splitting reactions. According to various embodiments, the contemplated reactor and method may be used for the production of carbon monoxide through the splitting of carbon dioxide. Other embodiments may also be adapted to benefit other similar reactions, both those known in the art as well as reactions that would be impractical using conventional reactors and methods.

FIG. 1 illustrates a basic two-step CeO₂ thermochemical cycle that operates at equilibrium. In this idealized cycle, the oxygen chemical potentials in the gas and solid phases are equal throughout (i.e., ½ μ_O2,gas=μ_O,solid). This is analogous to the Carnot cycle, maximizing efficiency for a set of boundary conditions. Two thermodynamic potentials typically drive the two steps: MO_x thermal reduction to an extent 8R, and re-oxidation or water splitting. These thermodynamic potentials are: (1) temperature (T) or temperature difference (ΔT), and (2) the oxygen chemical potential μ_O2,gas, usually via an inert gas sweep in TR, and via a steam sweep in WS.

FIG. 2 shows a schematic view of a non-limiting example of the contemplated two-step thermo-electrochemical (TEC) cycle 228, as well as the contemplated layered reactive element 200 that makes this TEC cycle 228 possible. According to various embodiments, the contemplated method comprises using solar heat and an alternating electrochemical potential (V) to assist both reduction and re-oxidation steps. It should be noted that both steps include both heat and electrical inputs.

Physically, to enable hybridization with electrical input in the TEC hybrid cycle 228, the contemplated layered reactive elements 200 replace the “bare” MO_x from the basic TC cycle. According to various embodiments, the layered reactive element 200 comprises a metal oxide core 202, an outer layer 206, and an ion conductor layer 204 in between the metal oxide core 202 and the outer layer 206. Each will be discussed in turn, below. Additionally, the layered reactive element 200 can be described as having two “modes”, a TEC reduction mode 214 and a TEC oxidation mode 216. As will be discussed below, the contemplated TEC cycle 228 comprises at least one layered reactive element 200 cycling between these two modes.

In the context of the present description and the claims that follow, a metal oxide core 202 refers to a core made of a redox-active metal oxide material that is a mixed ionic-electronic conductor (MIEC), meaning it can conduct both ions and electrons. Many of these MIEC MO_x formulations are in the perovskite family, with the general unit formula ABO₃, where “A” and “B” denote metals in two types of sites in the crystal lattice. In some embodiments, both sites can feature one or more substitutions. Specific examples include, but are not limited to, CAM28, La_xSr_1-xCo_yM_1-yO_3-δ (M=Mn, Fe), CaTi_0.2Mn_0.8O_3-δ (CTM28), La_0.7Sr_0.3Mn_0.9X_0.1O₃, (X=Ce, Cr, Al, Ga, Ni), CAM28-like formulations where iron (Fe) replaces aluminum (Al) as a substituent, and other MO_x formulations in the TEC target ΔH range.

One of the advantages of the contemplated TEC hybrid cycle 228, compared to the basic two-step STCH, is that it features a significantly wider MO_x properties space—a space where many candidates already exist and many more are likely to be found. Beyond MO_x availability, the expanded MO_x options may enable a MO_x selection based on cost and supply-chain security, such as focusing on earth-abundant metals and oxides that can be sourced and refined domestically.

Like the metal oxide core 202, the outer layer 206 is also an MIEC. In some embodiments, the outer layer 206 comprises a material that does not appreciably redox during the process, due to it having a high reduction enthalpy. Examples include, but are not limited to, ceria (e.g., gadolinium-doped ceria or GDC) and many other oxides. In other embodiments, the outer layer 206 may be composed of a redox-active material. As a specific example, in one embodiment, the outer layer 206 is composed of the same MIEC material as the metal oxide core 202.

Porosity may be advantageous for the outer layer 206. According to various embodiments, this outer layer 206 is thicker than the ion conductor layer 204, but is still relatively thin (i.e., roughly 100 microns). As shown, the outer layer 206 is communicatively coupled to a current collector 208, such that a voltage may be applied between the metal oxide core 202 and the outer layer 206. This current collector 208 may be any conductor known in the art that is chemically, thermally, and mechanically compatible with the outer layer 206. As will be discussed with respect to FIGS. 4A-4C, the layered reactive element 200 may have many different shapes, some of which require the current collectors 208 to take a different form.

The ion conductor layer 204 is sandwiched between the metal oxide core 202 and the outer layer 206. According to various embodiments, the ion conductor layer 204 comprises a material that has good oxygen ion conductivity, but is an electron insulator. Examples include, but are not limited to, yttria-stabilized zirconia. The ion conductor layer 204 is really thin in some embodiments, on the order of 5-10 microns. Generally, the thinner the ion conductor layer 204 the better, so long as it is fully dense, without pores through which gas could permeate. It should be noted that while various embodiments may use these and other materials for the core and the two layers, the materials should be mutually compatible and able to withstand the process temperatures.

The hybrid thermo-electrochemical cycle 228 contemplated herein switches between a reduction step and a re-oxidation step. These two steps correspond to two “modes” of the layered reactive element 200, the TEC reduction mode 214 and the TEC oxidation mode 216.

According to various embodiments, the TEC reduction mode 214 of a layered reactive element 200 comprises the metal oxide core 202 having an increased chemical potential of oxygen 220 relative to a gas phase. This increased chemical potential drives O²⁻ ions out of the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206 and out into the gas phase as O2. The contemplated layered reactive element 200 is able to do this because the chemical potential of oxygen 220 in the metal oxide core 202 is increased relative to the gas phase by the application of a small negative bias voltage, the first bias voltage 210, between the metal oxide core 202 and the outer layer 206.

This is done while the layered reactive element 200 is being heated by a heat source 218 (e.g., direct or indirect solar, electrical heating, etc.). Specifically, entering the TEC reduction mode 214 requires the application of the first bias voltage 210 between the metal oxide core 202 and the outer layer 206, and that the temperature be above a threshold reduction temperature 230, hereinafter referred to as T_TR. Advantageously, the resulting 8R is higher than would be possible with temperature alone (for identical gas phases), according to various embodiments.

According to various embodiments, the TEC oxidation mode 216 of a layered reactive element 200 comprises the metal oxide core 202 having a decreased chemical potential of oxygen 220 relative to the gas phase. This decreased chemical potential drives oxygen from an input gas 226 (e.g., steam, carbon dioxide, etc.) back into the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206. This leaves behind a gas product 222 (e.g., H₂, CO, etc.). The contemplated layered reactive element 200 is able to do this because the chemical potential of oxygen 220 in the metal oxide core 202 is decreased relative to the gas phase by the application of a small positive bias voltage, the second bias voltage 212, between the metal oxide core 202 and the outer layer 206.

As in the TEC reduction mode 214, the TEC oxidation mode 216 is achieved while the layered reactive element 200 is being heated by a heat source 218 (e.g., direct or indirect solar, electrical heating, etc.) to a temperature that is above a threshold oxidation temperature 232, hereinafter referred to as T_TO. It is important to note that the first bias voltage 210 and the second bias voltage 212 are of opposite polarity. In some embodiments they may be of equal magnitude, while in other embodiments they may have different magnitudes.

According to various embodiments, the layered reactive element 200 can be driven through a TEC cycle 228 through the application of temperatures and bias voltages, toggling the layered reactive element 200 between the TEC oxidation mode 216 and the TEC reduction mode 214. In application, this process may be driven by a controller (see controller 504 in FIGS. 5A and 5B), as will be discussed below. As previously discussed, both of these modes require the input of heat (to reach a threshold temperature) and electricity (to modify the chemical potential of oxygen in the metal oxide core 202).

In some embodiments, the TEC cycle 228 may comprise the layered reactive element 200 moving between two temperatures, T_TO (the threshold oxidation temperature 232) and T_TR (the threshold reduction temperature 230). In other embodiments, the temperature of the layered reactive element 200 may be held at or above the higher of the two temperatures (e.g., T_TR). As will be discussed, operating at two temperatures may be impractical in some reactor architectures, as an important feature of the contemplated thermo-electrochemical reactor 500 is the ability to take advantage of sudden energy opportunities, thus needing to get to a temperature quickly. This may be difficult in reactor architectures that do not maintain two different temperature zones.

Assuming the threshold temperature is satisfied, the TEC cycle 228 is driven by the sequential application of the first bias voltage 210 and the second bias voltage 212. Applying the first bias voltage 210 across the metal oxide core 202 and the outer layer 206 will increase the chemical potential of oxygen 220 in the metal oxide core 202, driving O²⁻ ions out of the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206 and into the gas phase as O2. This may be facilitated by keeping the partial pressure of O2 in the environment around the layered reactive element 200 low. This may be accomplished by displacing the O2-rich atmosphere out and away from the layered reactive element 200 by introducing a sweep gas 224.

Next, the layered reactive element 200 is put into the TEC oxidation mode 216 by applying the second bias voltage 212 between the metal oxide core 202 and the outer layer 206. The first bias voltage 210 and the second bias voltage 212 are of opposite polarity. As this is being done, an input gas 226 is introduced to the layered reactive element 200 (e.g., an input gas 226 is introduced to an enclosed area containing the layered reactive element 200, etc.). The input gas 226 is the gas that is going to be split by the TEC cycle 228 (e.g., water in the form of steam, carbon dioxide, etc.). The second bias voltage 212 reduces the chemical potential of oxygen 220 in the metal oxide core 202, thereby driving oxygen from the input gas 226 into the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206, leaving behind a gas product 222 (e.g., H₂, CO, etc.) in the gas phase. Finally, the gas product 222 is extracted by displacing it with a sweep gas 224, which may or may not be the same sweep gas 224 as used to displace O2 during the reduction step.

In some embodiments, the sweep gas 224 may be air, while in other embodiments the sweep gas 224 may be an inert gas. In still other embodiments the sweep gas 224 may be steam, which can be easy to separate from the extracted gas (e.g., O2, the gas product 222, etc.) by condensing the steam into liquid. It should be noted that while this discussion was done in the context of a single layered reactive element 200, a thermo-electrochemical reactor 500 may comprise a plurality of layered reactive elements 200.

FIG. 3 shows an equilibrium TEC cycle in δ-V space, quantifying a non-limiting example of a layered reactive element 200, specifically an embodiment that uses CaAl_0.2Mn_0.8O₃ (hereinafter CAM28), a perovskite MO_x developed for TC energy storage. A basic TC cycle (e.g., the cycle shown in FIG. 1) using CAM28 as the redox-active MO_x is not possible, because ΔH_CAM28≈153 KJ/mol O, making the re-oxidation step endothermic and not thermodynamically favored. However, in the contemplated TEC hybrid cycle shown in FIG. 3, the electrochemical potential bridges the CAM28 energy gap in both cycle steps. In the reduction step, this energy gap manifests as a δ_R lower than target. Without a bias (e.g., V=0, T_TR=800° C., in air), δ_R would be roughly 0.05. With a first bias voltage 210 of V=−0.35 V the extent of reduction increases to a δ_R of about 0.3, which is close to the oxygen vacancy solubility limit for CAM28. Essentially, the bias is an additional tuning parameter for the reaction that allows a desired δ_R to be “dialed in”, according to various embodiments.

According to some embodiments, the bias may not be constant because the cycle and each step individually follow an equilibrium curve. In practice, a small overpotential may be needed to achieve a desired reaction rate (and overcome transport losses, etc.), as the reaction at equilibrium proceeds at an infinitely small rate. The re-oxidation step is not spontaneous without a bias, the reaction being endothermic and requiring an energy input of ˜95.5 KJ/mol H₂, which in the TEC cycle 228 is provided by a small (also variable) bias in the opposite direction of the first bias voltage 210. This is the second bias voltage 212. In addition to making re-oxidation possible, the second bias voltage 212 also enables a tuning parameter: the H₂/steam ratio in the gas product 222 (i.e., the conversion yield).

The δ-V diagram of FIG. 3 also illustrates the optimization space: a lower re-oxidation temperature (T_TO) would, thermodynamically speaking, require a lower bias (i.e., bringing the two voltage absolute values closer together) and would also increase the proportion of thermal work input in the cycle. However, practical reaction rates decrease with temperature, offsetting some of the thermodynamic advantage. Increasing ΔH_MOx above that of CAM28, for example, would also bring the two voltages closer to each other in absolute value. Reaction yield and reaction rates are examples of other optimization parameters accessible to the TEC hybrid cycle 228, according to various embodiments.

Many of the TEC hybrid cycle benefits, compared to the baseline two-step TC cycle, stem from the addition of a controllable/tunable thermodynamic potential to the process, effectively removing many constraints inherent to baseline TC cycles.

For example, the TEC hybrid cycle 228 can offer significantly higher productivity (e.g., ˜5× to 10×) per cycle and per unit MO_x than conventional TC cycles, owing to a δ_R≥0.3 (i.e., at T_TR≤800° C., FIG. 3, within third generation CST capability). High δ_R lowers MO_x inventory/cost. In conjunction with a tunable ΔT=T_TR−T_TO, a high δ_R makes the extensive solid-solid heat recovery that is typical for basic TC cycles, unnecessary, according to various embodiments.

Another benefit of the TEC hybrid cycle 228 contemplated herein is a significantly relaxed reduction step O₂ partial pressure (pO2) limits, in some embodiments up to and including using ambient air as a sweep gas 224 (as shown in FIG. 3). This can provide a significant cost and system complexity reduction compared to sweeping with an inert gas.

The contemplated TEC hybrid cycle 228 enables a tunable reaction yield. In some embodiments, it may be tuned up to and including yields sufficiently high to eliminate the need for H₂/steam separation and steam recycling (in the case of water splitting), yet another system complexity reduction.

Furthermore, the contemplated TEC hybrid cycle 228 has eliminated re-oxidation exotherm. Necessary in TC cycles, an exotherm is not easily recovered, limiting practical efficiency to less than 50% (e.g., ˜75 kWht/kg H₂). Its elimination enables a practical energy input of <50 kWh_e+t/kg H₂, with at least half supplied as heat in some embodiments.

One benefit of the TEC hybrid cycle 228 contemplated herein is the hybridization enables both thermal steps to be endothermic, which is a thermodynamic benefit in a partially heat-driven cycle. In purely heat-driven TC cycles, the high temperature needed for chemical kinetics inhibits the exothermic re-oxidation step, which would ideally operate at the lowest possible temperature. In TEC, high temperature is advantageous throughout the cycle.

The contemplated TEC hybrid cycle 228 also facilitates a much lower temperature target (e.g., 600-800° C. of FIG. 3) than for TC cycles (e.g., 1400-1600° C. of FIG. 1), easing thermal stress on reactive components, enabling low-cost construction materials, avoiding the need for secondary solar concentrators, and allowing indirect illumination receivers and flexibility in reactor design. Also, the contemplated TEC hybrid cycle results in significantly broader MO_x properties space than for pure TC cycles, enabling the use of numerous earth-abundant oxide perovskites, with cost and domestic supply benefits.

FIGS. 4A-4C show cross sectional views of three non-limiting examples of layered reactive elements 200 having different architectures. While one architecture may be superior compared to another in one set of circumstances, under different circumstances a different architecture may be preferable. Considerations such as capacity, ion and electron conductivity, heat transfer, durability, ease of manufacture at scale, and the like may dictate which architecture is best suited for a particular use case.

It should also be noted that the following three architectures do not represent the broad range of possible shapes, sizes, and arrangements possible for the contemplated layered reactive element 200. These three non-limiting examples each demonstrate useful properties, but should not be taken as limitations.

FIG. 4A shows a cross-sectional view of a non-limiting example of a planar layered reactive element 400. As shown, the planar layered reactive element 400 is substantially planar. In the context of the present description and the claims that follow, “substantially planar” means that the principal dimension of the element (i.e., length) is at least an order of magnitude larger than the tertiary dimension (i.e., thickness), and the secondary dimension (i.e., width) is at least three times larger than the tertiary dimension. The element is flat, to within 15 degrees, according to various embodiments.

One of the more influential dimensions for this architecture is the thickness of the internal MIEC metal oxide core 202. In general, thicker is better for capacity, but worse for ion and electron conductivity as well as heat transfer. The balance will depend on the specific material choices and the operating temperature. According to some embodiments, a 0.5 mm thickness is a good estimate. In some embodiments, the length is roughly 75 mm, while in other embodiments the length may be greater, which would be both feasible and desirable in a scaled-up device. For example, in some scaled up embodiments, lengths of the order of ˜1 m are feasible and may also be desirable.

According to various embodiments, the fabrication of the layered reactive elements 200 rests on well-established, commercially available techniques from the tubular fuel cell field, such as extrusion, dip coating, and wet powder spray. These techniques have been used to develop commercially available layered structures that are thin enough to minimize transport losses, but durable enough to rapidly heat and cool. For example, cycling results with tubular layered reactive elements 402 (shown in FIG. 4B) have achieved heating and cooling rates between 300-950° C./min, which may be employed in the contemplated TEC hybrid cycle for nimble response to available solar energy, according to various embodiments.

FIG. 4B shows a cross sectional view of a non-limiting example of a tubular layered reactive element 402. According to various embodiments, the hollow tubular geometry provides a number of advantages. This architecture tends to be more durable because the characteristic dimension that limits or determines thermal shock issues that sometimes arise is very small (e.g., three millimeters). Additionally, the layers themselves can be very thin, with a coiled current collector 208 running up the hollow interior, making contact with the metal oxide core 202. This architecture may provide a desirable combination of large surface area and thin layers.

Like the planar layered reactive element 400, the tubular layered reactive element 402 may present scalable fabrication advantages. A specific, non-limiting example of a fabrication process for a tubular layered reactive element 402 begins with extruding the outer layer 206 material (e.g., GDC) as a tube. This will act as support for the rest of the element. After drying (e.g., 1 week) and pre-firing (e.g., 15 hours at 1100° C.), the tube is leak checked, the filled with a slurry made of the ion conductor layer 204 material (e.g., YSZ). The interior of the tube is coated with the YSZ, which is drained. The tube may be rolled to ensure a uniform layer, and then is sintered (e.g., 90 hours at 1375° C.). The tube is again leak checked, and then filled with a slurry of the metal oxide core 202 material (e.g., LSM). Again, a thin layer coats the interior of the tube and the rest is drained. The tube is again sintered (e.g., 80 hours at 1100° C.). After a final leak check, the current collectors 208 are added (e.g., a silver coil running up the hollow interior, a silver wire wrapped around the exterior, etc.). It should be noted that these steps may be modified, according to various embodiments. For example, in one embodiment, the ion conductor layer 204 and metal oxide core 202 may be formed as layers on the outside of the so-called tubular outer layer 206.

FIG. 4C shows a cross sectional view of a non-limiting example of a button layered reactive element 404. The button architecture has the advantage of easy fabrication and it requires much less material than other methods such as extrusion, making it a good choice for development work that requires rapid iteration and experimental reliability. According to various embodiments, the button layered reactive element 404 is essentially two elements fused together—it has two metal oxide cores 202, two ion conductor layers 204, and two outer layers 206.

A non-limiting example of the fabrication process for the button layered reactive element 404 begins with forming and sintering the metal oxide core 202 layers (e.g., LSM, ˜400 μm thick). According to various embodiments, the metal oxide core 202 layer is formed using a dry pressing technique that compresses powder (here, powdered LSM) into a pellet without requiring additional materials.

The ion conductor layer 204 material (YSZ, ˜10 μm thick) is deposited on top of the metal oxide core 202 and then sintered again. The deposition of the ion conductor layer material may be deposited as a slurry applied with a spray gun.

Finally, the outer layer 206 material (e.g., GDC, ˜10 μm thick) is deposited on top and sintered again, using the same technique used to deposit the ion conductor layer 204. The two halves are joined with a metallic contact sandwiched between the two metal oxide core 202 layers, and contacts are added to the outer layers 206, according to various embodiments.

FIGS. 5A and 5B are schematic views of non-limiting examples of an electrically heated TEC reactor 500. Specifically, FIG. 5A is a schematic view of a non-limiting example of an electrically heated TEC reactor 500 having stationary reactive elements. FIG. 5B is a schematic view of a non-limiting example of an electrically heated TEC reactor 500 with moving reactive elements.

According to various embodiments, the TEC reactor 500 comprises an insulated housing 502 and a plurality of layered reactive elements 200 inside the insulated housing 502. The insulated housing 502 also comprises at least one gas inlet 506 and at least one gas outlet 508, which are used to introduce gases (e.g., input gas 226, sweep gas 224, etc.) and through which gases may be extracted (e.g., gas product 222, sweep gas 224, O₂, etc.).

As shown, the TEC reactor 500 also comprises a controller 504. According to various embodiments, the controller 504 is communicatively coupled to the metal oxide core 202 and the outer layer 206 of each of the layered reactive elements 200, and is responsible for applying the first bias voltage 210 and the second bias voltage 212, driving the hybrid thermo-electrochemical cycle 228. In some embodiments, the controller 504 may also control the internal temperature by manipulating the heat source 218, and may also operate valves at the gas inlets 506 and gas outlets 508. For example, in one embodiment, the controller 504 may be configured to displace the gas product 222 within the insulated housing 502 with a sweep gas 224, and then extracting the displaced gas product 222 through a gas outlet 508. According to various embodiments, the controller 504 may be a microcontroller or other computing device, as is known in the art.

In some embodiments, the layered reactive elements 200 within the insulated housing 502 may remain motionless with respect to the insulated housing 502 as the controller 504 cycles the layered reactive elements 200 between the TEC oxidation mode 216 and the TEC reduction mode 214. See, for example, the TEC reactor 500 of FIG. 5A. This reactor architecture has the advantage of simplicity, with fewer moving parts and thus fewer opportunities to break down. However, the output of such a reactor would be intermittent, producing a batch of gas product 222 with every iteration of the hybrid thermo-electrochemical cycle 228.

In other embodiments, the layered reactive elements 200 within the insulated housing 502 may be movable, allowing for a continuous process to be achieved. See, for example, the “labyrinth” reactor architecture of FIG. 5B.

According to various embodiments, the Labyrinth reactor (hereinafter LR) uses thin, rod-shaped MO_x reactive elements, and is compatible with the components of the contemplated method such as layered structures (e.g., layered reactive element 200), solar input, and a variable bias, making the long-sought two-step hybrid STCH MO_x cycle feasible. Having been developed for a basic TC cycle, the LR serves as an excellent starting point for a TEC reactor 500 design. One of the already demonstrated features of the LR is its ramp rate, including extensive testing on the “bare” reactive elements themselves, which have shown resilience for heating/cooling rates of ˜1000° C./min.

In contrast to the static reactor architecture of FIG. 5A, the LR design has all parts of the hybrid thermo-electrochemical cycle 228 being performed at the same time within the insulated housing 502. For example, when at least one layered reactive element 200 is in the TEC oxidation mode 216, at least one other layered reactive element 200 is in the TEC reduction mode 214, elsewhere in the LR. In a specific example, the entire insulated cavity may be roughly 18.5 cm wide.

The main cost drivers for STCH reactors are the MO_x inventory and the reactor size itself. Achieving water splitting using comparatively low ΔH MO_x formulations is a game-changer for STCH, in terms of both performance and cost. It has been demonstrated that it is possible to achieve δR˜0.3 with CAM28 and other MO_x formulations, as well as short reaction times (e.g., ˜15 s), and low at-scale MO_x costs (e.g., ˜$1-2/kg). For such high δR and short cycle times, conservatively assuming τ=3 min, the MO_x inventory is minimal—the mass of MO_x is roughly 0.4 kg/kW H₂. Depending on realized cycle times (e.g., as low as 60 s), these factors may enable power-dense TEC reactors with an outstanding specific H₂ output (e.g., ˜3-9 MWH₂/m³).

Some embodiments, and on this basis, preliminary thermodynamic and cost models suggest that the contemplated reactor could have a breakthrough capital cost (CAPEX) of roughly $10/kW H₂ output, a minimal energy input of less than <50 kWhe+t/kg H₂, and an outstanding cold start time of less than 5 min. The above factors can enable cost-effective intermittent/opportunistic TEC hybrid operation. According to one embodiment, an intermittent TEC H₂ production scenario could be used in conjunction with dedicated, minimal-cost hybrid concentrating solar (heat) and photovoltaic plants, without storage, and potentially even without DC/AC conversion.

Another scenario, made possible by the low CAPEX, is operation in conjunction with (existing) concentrating solar power (CSP) plants. CSP plants routinely aim a fraction of the heliostats away from the receiver (a practice called “defocusing”), for the purpose of not exceeding the receiver heat flux rating. Typically, 5-15% of the incident solar resource is defocused (i.e., not used) in CSP plants. Taking advantage of defocused radiation, usually concurrent with low-cost grid sourced electricity, the contemplated low CAPEX TEC reactors could be installed as add-on units, to produce H₂ and create value out of existing but unutilized capital assets.

Two-step MO_x cycles are theoretically the simplest and the most efficient. Research has focused on lowering practical TR temperatures (and associated costs) from ˜1500° C., and relaxing TR pO2 (and associated costs) upward from ˜10 Pa. Multi-step hybrid cycle temperatures are lower than in two-step. The main challenge of a hybrid two-step MO_x cycle is the design of a practical reactor implementation. The TEC hybrid cycle 228 addresses the main challenges that constrain STCH reactor design, namely the TR temperature and pO2, and expands the possibilities both in terms of reactor construction materials and reactors as solar receivers. The latter can now include indirectly heated reactors, which are not typically feasible at 1400-1500° C. Another reactor simplification and a cost saving measure is using air to sweep the O2 from the TR step, in some embodiments.

Beyond STCH, TEC also offers advantages compared to electrochemical H₂ production, such as low- and high temperature electrolysis. Briefly, TEC has the potential to meet all three criteria (i.e., CAPEX, efficiency, response), whereas electrochemical approaches do not. Specifically, low temperature electrolysis CAPEX status and targets, especially as reflected in use cases, do not offer a path toward operation at a low (or even medium) capacity factor. High temperature electrolysis shares the capacity factor challenge, precipitated by a persistently slow on/off response.

FIG. 6 is a process flow of a non-limiting example of a method for carrying out a hybrid thermo-electrochemical cycle 228 using a layered reactive element 200. First, the layered reactive element 200 is heated with a heat source 218. See ‘step 600’. According to various embodiments, the layered reactive element 200 comprises a metal oxide core 202 that is redox-active and is a mixed ionic-electronic conductor (MIEC), an outer layer 206 that is also an MIEC, and an ion conductor layer 204 between the metal oxide core 202 and the outer layer 206. The heat source 218 may be solar-based (e.g., direct solar, indirect solar, etc.) or electric heating from some other power source, according to various embodiments.

Next, the chemical potential of oxygen 220 in the metal oxide core 202 is increased (relative to the gas phase) through applying a first bias voltage 210 between the metal oxide core 202 and the outer layer 206. See ‘step 602’. Increasing the chemical potential of oxygen 220 in the metal oxide core 202 drives O2− ions out of the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206 and into the gas phase as O2.

The layered reactive element 200 is then exposed to an input gas 226. See ‘step 604’. In some embodiments, the input gas 226 may be used to displace the O2 being released from the metal oxide core 202. In some embodiments, the input gas 226 may be water, in the form of steam. In other embodiments, the input gas 226 may be carbon dioxide. In still other embodiments, a different input gas 226 may be used.

After the input gas 226 has been introduced to the layered reactive element 200, the chemical potential of oxygen 220 in the metal oxide core 202 is decreased through the application of a second bias voltage 212 between the metal oxide core 202 and the outer layer 206. See ‘step 606’. This decrease in the chemical potential of oxygen 220 in the metal oxide core 202 drives oxygen from the input gas 226 into the metal oxide core 202, through the ion conductor layer 204 and the outer layer 206, leaving a gas product 222 behind in the gas phase. The first bias voltage 210 and the second bias voltage 212 are of opposite polarity.

Finally, the gas product 222 is extracted by displacing the gas product 222 with a sweep gas 224. See ‘step 608’. In some embodiments, the sweep gas 224 may be steam, while in others it may be air or an inert gas.

It will be understood that implementations are not limited to the specific components disclosed herein, as virtually any components consistent with the intended operation of layered reactive elements in a thermo-electrochemical reactor and method for using the same may be utilized. Accordingly, for example, although particular systems, methods, and/or devices for oxidation and reduction may be disclosed, such components may comprise any shape, size, style, type, model, version, class, grade, measurement, concentration, material, weight, quantity, and/or the like consistent with the intended operation of layered reactive elements in a thermo-electrochemical reactor and method for using the same may be used. In places where the description above refers to particular implementations of layered reactive elements in a thermo-electrochemical reactor and method for using the same, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these implementations may be applied to other reactors.

Claims

1. A thermo-electrochemical reactor, comprising:

at least one layered reactive element, each layered reactive element comprising: a metal oxide core that is redox-active and is a mixed ionic-electronic conductor (MIEC), an outer layer that is also an MIEC, an ion conductor layer between the metal oxide core and the outer layer, a TEC reduction mode, and a TEC oxidation mode;

a controller communicatively coupled to the metal oxide core and the outer layer of each of the at least one layered reactive element;

a heat source;

wherein, for each layered reactive element, the TEC reduction mode comprises the metal oxide core having an increased chemical potential of oxygen relative to a gas phase that drives O2− ions out of the metal oxide core, through the ion conductor layer and the outer layer and into the gas phase as O2, with the chemical potential of oxygen in the metal oxide core being increased relative to the gas phase through applying a first bias voltage between the metal oxide core and the outer layer;

wherein, for each layered reactive element, the TEC oxidation mode comprises the metal oxide core having a decreased chemical potential of oxygen relative to the gas phase that drives one of oxygen from steam and oxygen from carbon dioxide back into the metal oxide core, through the ion conductor layer and the outer layer, leaving a gas product that is one of H2 in the gas phase and CO in the gas phase, with the chemical potential of oxygen in the metal oxide core being decreased relative to the gas phase through applying a second bias voltage between the metal oxide core and the outer layer;

wherein the controller is configured to drive the thermo-electrochemical reactor to carry out a TEC cycle by alternating between applying the first bias voltage and applying the second bias voltage to at least one layered reactive element while the at least one layered reactive element is being heated by the heat source, cycling the at least one layered reactive element between the TEC reduction mode and the TEC oxidation mode;

wherein the first bias voltage and the second bias voltage have opposite polarity.

2. The thermo-electrochemical reactor of claim 1, wherein the at least one layered reactive element is hollow.

3. The thermo-electrochemical reactor of claim 1, wherein each layered reactive element of the at least one layered reactive element comprises two metal oxide cores, two ion conductor layers, and two outer layers.

4. The thermo-electrochemical reactor of claim 1, wherein the layered reactive element is substantially planar.

5. The thermo-electrochemical reactor of claim 1, wherein the metal oxide core comprises a perovskite.

6. The thermo-electrochemical reactor of claim 5, wherein the metal oxide core comprises CAM28.

7. The thermo-electrochemical reactor of claim 1, wherein the outer layer is gadolinium-doped ceria (GDC).

8. The thermo-electrochemical reactor of claim 1, wherein the ion conductor layer is yttria-stabilized zirconia.

9. The thermo-electrochemical reactor of claim 1:

wherein the thermo-electrochemical reactor comprises a plurality of layered reactive elements;

wherein at least one layered reactive element of the plurality of layered reactive elements is in the TEC oxidation mode while at least a different layered reactive element of the plurality of layered reactive elements is in the TEC reduction mode; and

wherein the plurality of layered reactive elements move throughout the thermo-electrochemical reactor as the controller drives the thermo-electrochemical reactor to carry out the TEC cycle.

10. The thermo-electrochemical reactor of claim 1:

wherein the thermo-electrochemical reactor further comprises an insulated housing, a gas inlet, and a gas outlet;

wherein the at least one layered reactive element remains motionless with respect to the insulated housing as the controller cycles the at least one layered reactive element between the TEC oxidation mode and the TEC reduction mode.

11. The thermo-electrochemical reactor of claim 1, wherein the heat source is solar-based.

12. The thermo-electrochemical reactor of claim 1, wherein the controller is further configured displace the gas product with a sweep gas, the displaced gas product extracted through a gas outlet.

13. The thermo-electrochemical reactor of claim 12, wherein the sweep gas is steam.

14. A method for carrying out a hybrid thermo-electrochemical cycle using a layered reactive element, comprising:

heating the layered reactive element with a heat source, the layered reactive element comprising a metal oxide core that is redox-active and is a mixed ionic-electronic conductor (MIEC), an outer layer that is also an MIEC, and an ion conductor layer between the metal oxide core and the outer layer;

increasing a chemical potential of oxygen in the metal oxide core, relative to a gas phase, thereby driving O2− ions out of the metal oxide core, through the ion conductor layer and the outer layer and into the gas phase as O2, the chemical potential of oxygen in the metal oxide core being increased relative to the gas phase through applying a first bias voltage between the metal oxide core and the outer layer;

exposing the layered reactive element to an input gas, the input gas displacing the O2 in the gas phase;

decreasing the chemical potential of oxygen in the metal oxide core, relative to the gas phase, thereby driving oxygen from the input gas into the metal oxide core, through the ion conductor layer and the outer layer, leaving a gas product in the gas phase, with the chemical potential of oxygen in the metal oxide core being decreased relative to the gas phase through applying a second bias voltage between the metal oxide core and the outer layer; and

extracting the gas product by displacing the gas product with a sweep gas;

wherein the first bias voltage and the second bias voltage have opposite polarity.

15. The method of claim 14, wherein the sweep gas is steam.

16. The method of claim 14, wherein the input gas is one of steam and carbon dioxide, and wherein the gas product is one of H2 and CO.

17. The method of claim 14, wherein the metal oxide core comprises a perovskite.

18. The method of claim 14, wherein the metal oxide core comprises CAM28.

19. The method of claim 14, wherein the outer layer is gadolinium-doped ceria (GDC).

20. The method of claim 14, wherein the ion conductor layer is yttria-stabilized zirconia.