PROCESS TO MAKE IRON BASED ELECTROCATALYST, AN ANODE MATERIAL, AN ELECTROCHEMICAL SYSTEM AND A PROCESS FOR WATER CONVERSION, CATALYSIS AND FUEL GENERATION
This invention provides a simple approach for the straightforward and direct preparation of iron-oxide based electrocatalytic materials film (FeOx—Ci) on a simple Fe substrate by controlled surface-anodization and/or self-deposition in simple and low-cost carbonate buffer. The FeOx—Ci based electrocatalysts may advantageously be employed as electrode and as anode material in water oxidation, water conversion systems and fuel generation assemblies. The FeOx—Ci exhibits remarkably low over potential (η≈360) for anodic oxygen evolution relative to other Fe-oxide based catalysts, and show very high activity and stability for long-term water electrolysis operation.
The present invention describes a process for forming and electro-assembling of metal oxide electrocatalytic material, a process to prepare an anode material, an electrochemical cell, and a process to convert water by electrochemical technology into oxygen and protons, via controlled surface-anodization and/or self-deposition of a simple iron surface and/or iron-derived substrates and alloys.
Water, using renewable electricity and/or solar energy, can be converted into oxygen and protons via processes referred to as catalytic water oxidation or water splitting in an electrochemical system or via photo-electrochemical (PEC) methods. This is a promising technology and a feasible process for the direct conversion of light energy into renewable fuels and cheap energy carriers using simple water. The beauty of water splititng is the release of four electrons and four protons per O2 trunover, that can be used either to make hydrogen as clean and high energy density fuel or in combination of CO2 to direclty reduce it, and to convert it into useul nonfossil feuls and chemical energy carriers (
Many millions of years ago, nature has devised an efficient system to convert water and CO2 into energy storable substances using sun light. In natural photosynthesis, the catalytic oxidation of water in photosystem II (PS-II) is facilitated by the presence of MnCaO based water oxidation material/complex that splits water with high efficiency and at a tremendous rate. Scientists are trying hard to mimic this state-of-the-art material in labs using both material-science and molecular approaches to be obtained from cheap sources and earth-abundant elements.
Ru-oxide and Ir-oxide are established and benchmarking materials for electrochemical water splitting. But they are too expensive to be employed on large scale application. Recently, catalytic materials based on oxides of the abundant first row transition metals such as Ni, Co, Mn and Cu have been emerged as substitute of the noble metals based electrocatalysts.
These transition metal-oxide electrocatalysts were developed by conducting substrates from metal ions solutions under electrochemical conditions. The presence of metal ions is a prerequisite for their activity and long-term water electrolysis performance and metal ions may possibly interact to contaminate and poison the cathode for the reduction reaction. In order to avoid the metal ions interaction, membranes or separators are usually employed, which make the system more complex and introduce resistance and diffusion limitations. Thus, new materials and methods are required to develop high activity water oxidation electrocatalysts. At the same time, there is a need to develop easily accessible and robust water oxidation catalytic systems operating at low overpotential with high rate turnover for anodic oxygen evolution and performing with high stability for long-term application.
Applicant discovered a simple method for the formation of nanoscale metals-based and metal-oxides based electrocatalysts to be advantageously employed as electrode and as anode materials in water oxidation, water conversion systems and fuel generation assemblies.
BRIEF SUMMARY OF THE INVENTIONIron is interesting metal and it is the most abundant element among transition metals in the earth's crust. Iron is also the main component of many biological systems and enzymes for oxygen activation. Iron-oxide (Fe2O3) is a very good candidate for photocatalytic water oxidation, however iron or iron-oxide based materials have been scarcely explored for anodic oxygen evolution reactions.
It is difficult to prepare iron-oxide layer via electrodeposition as it requires FeII/FeIII ions which easily precipitates out from water under near-neutral conditions and Iron-oxide is not stable in low pH solutions.
The present invention is a process for the direct preparation, electrodeposition and surface-assembling of iron-based and/or iron-oxide based electrocatalysts and/or anode materials by surface-anodization and/or self-deposition of an amorphous iron and/or iron-derived substrates and alloys in simple but not limiting to bicarbonate/carbonate (HCO3−/CO32−) buffer system.
Next, the present invention comprising the steps of: (1) surface cleaning of simple amorphous iron and/or iron-derived substrates and alloys with neat water, following cleaning with dilute acid and washing with water, and (2) immersing the clean amorphous iron and/or iron-derived substrates and alloys as an anode in an aqueous bicarbonate/carbonate (HCO3−/CO32−) buffer system at a pH in the range from 8.5 to 13.5, and (3) applying a current over the anode and cathode suitable for electrolytically surface-anodizng and/or self-depositing the iron-based and/or iron-oxide based electrocatalysts and/or anode materials, and (4) using the thus obtained surface-assembled electrocatalytic material in a suitable electrolyte systems of water electrolysis and its conversion into fuel.
Further, the present invention relates to the use of the iron-derived material as an electrolysis catalyst applicable to a wide range of pH and variety of electrolyte systems.
Further again, the present invention relates to an iron-based and/or iron-oxide based catalytic electrode material having moderate water electrolysis overpotential (η) from 300 to 500 mV.
Further again, the present invention relates to an iron-based and/or iron-oxide based catalytic electrode material having very high activity and stability for long-term water electrolysis systems.
Further again, the present invention relates to simple and direct formation of an iron-based and/or iron-oxide based catalytic material thus avoiding the difficulties during electrodeposition from metal ions in the neutral and above neutral pH system that cause the precipitation and reduce catalytic formation and electro-activity.
Further again, the present invention relates to an iron-based and/or iron-oxide based material catalytically active in metal-ions free phosphate, borate, carbonate, hydroxide or other aqueous electrolytes.
Further, the present invention relates to an iron-based and/or iron-oxide based electrocatalytic materials with nanosclae surface morphology with an average particle size in the range of from 25 nm to 250 nm or more as determined by SEM microscopy.
Further again, the present invention relates to an iron-based and/or iron-oxide based materials whereby the surface nanoparticles have an average thickness of from 10 to 500 nm or more as determined by SEM microscopy.
The present invention is an electrochemical cell comprising an anode comprising the iron and/or iron-oxide nanoparticulate material according to the invention.
Further, the present invention relates to a process to convert water into oxygen, and releasing electrons and protons, comprising an electrochemical cell according to the invention, and applying a suitable voltage to the iron-based and/or iron-oxide derived anode and a cathode, using a power source.
Further, the present invention relates to a process of water conversion in an electrochemical cell according to the invention, using a suitable power source from renewable sources, hydel power, wind, and from solar energy.
Further, the present invention relates to a process of oxidation, catalysis, splitting, oxidation and conversion of water and for the fuel generation.
The nanoscale iron-based and/or iron-oxide based electrocatalyst is generated in a metal-ions free solution during constant-current electrolysis (CCE) at a current density of 5.0 mA cm−2 in carbonate buffer (pH≈11). The surface-assembling of iron-oxide (FeOx—Ci) electrocatalyst on simple iron substrate can be ascribed to the surface electrochemical process involving the surface oxidation to from Fen+ type surface species that quickly turned into metal hydroxide/oxide type composition on Fe surface. These initial nano-assemblies act as nuclei for the generation and growth of nano-structured FeOx—Ci electrocatalyst on simple iron substrate. (Studies are in progress to explore more insight into the mechanism of FeOx—Ci generation on Fe surface in carbonate buffer). Scanning electron microscope image shows nicely distributed nano-structures of FeOx—Ci on the entire surface of the anodized Fe substrate (
EDX (energy dispersive X-ray) measurements for the elemental composition show Fe and O in the FeOx—Ci electrocatalyst sample (
The surface composition of the nano particulate FeOx—Ci is examined by X-ray photoelectron spectroscopy (XPS). The elemental detection on the XPS survey for electro generated iron-oxide layer indicates the presence of iron, oxygen and carbon in the catalytic film (
For water oxidation catalysis using FeOx—Ci electrocatalyst, voltammetry and long-term water electrolysis experiments are undertaken in clean carbonate buffer solutions. The forward sweep voltammetry for the iron-oxide shows onset of the catalytic current for oxygen evolution at ˜1.59 V vs RHE (ηon=360 mV), following a sharp rise in the current density (
The repetitive potential sweeps for FeOx—Ci electrocatalyst sample reproduce the similar current density signatures for the 1st and 100th scan suggesting no noticeable degradation of FeOx—Ci system and representing remarkable stability and long-time activity of the new Fe-based electro catalyst (
Current—over potential (η vs log i) plot of the FeOx—Ci electrocatalyst during oxygen generation produces a Tafel slope of 47 mV dec−1 (
For long-term water electrolysis testing and stability performance of the FeOx—Ci based electro catalyst, electro catalytic experiments are conducted in clean metal ions free carbonate solution. We chose constant-current electrolysis (chronopotentiometry) experiments while preserving stable current densities of 15 mA cm−2 and 50 mA cm−2 and monitoring the potential response of the system at the same time. The FeOx—Ci electrocatalyst remains remarkably stable during high activity oxygen evolution at current densities of 15 mA cm−2. To achieve 15 mA cm−2, a very stable steady-state potential of ˜1.75 V (vs RHE) is preserved for 17 hours of the catalytic water electrolysis (
Meanwhile, a rich stream of oxygen bubble is also coming out of FeOx—Ci surface as monitored by online GC. Further, the current density is switched to a very high magnitude of 50 mA cm−2 which is maintained at just ˜2.15 V (vs RHE) in clean carbonate system (
A comparative analysis of different Fe-oxide based water oxidation eletrocatalysts and their electrochemical performance for oxygen evolution is presented in Table 1. It is evident that FeOx—Ci exhibits the lowest onset potential of 1.59 V vs RHE (η=360 mV) relative to other Fe-based catalysts. FeOOH type Fe-catalyst exhibits the highest onset over potential, i.e >1.70 V vs RHE. We show that the benchmark current density of 10 mA cm−2 is achieved at η≈470 mV for FeOx—Ci sample. Other Fe-oxide based catalysts exhibit much higher over potentials to reach 10 mA cm−2. Surface-generated FeOx—Ci system also shows the smallest Tafel Slope 47 mV dec−1, which is again lowest in the list of Fe-based eletro catalyst.
Claims
1. A method of making a catalytic comprising:
- providing an anode and a cathode in an electrochemical cell;
- cleaning the electrodes with acid wash and water;
- immersing the electrodes in an aqueous bicarbonate/carbonate buffer system at a pH ranging from 8.5 to 13; and,
- applying constant current or constant potential to the electrodes suitable to electrochemically produce surface anodizing leading to deposit of iron oxide on the surface of the anode.
2. The method of claim 1, wherein, the anode is made of iron metal, an iron alloy or an iron-derived material.
3. The method of claim 1, wherein the anode is coated with nanoparticles.
4. The method of claim 1, wherein the applied voltage is higher than 1.40 volts.
5. The method of claim 1, wherein the voltage is applied from 0.1 minutes to 24 hours or more.
6. The method of claim 1, wherein the applied current is above 0.1 milliampere per square meter of the surface of anode.
7. The method of claim 1, wherein the size of deposited particles ranges between 25 and 250 nm.
8. The method of claim 1, wherein the thickness deposited iron oxide on the anode is 5 to 250 nm.
9. The method of claim 1, wherein the electrolytic solution is free of transition metal ions.
10. A method of converting water into oxygen and releasing hydrogen comprising:
- providing the anode of claim 1 and a cathode in an electrochemical cell;
- applying a suitable voltage to split water molecules into electrons and protons to make hydrogen as fuel, energy carrier, chemical feedstock, or non-fossil fuel when combined with carbon dioxide.
Type: Application
Filed: Feb 11, 2016
Publication Date: Aug 17, 2017
Inventor: Khurram Saleem Joya (Lahore)
Application Number: 15/041,930