Method, Cell and Electrode for Hydrogen Production

Abstract

A hydrogen-producing cell includes a first and second electrode. The first electrode includes a cathode that includes a nickel single-atom graphdiyne porphyrin analogue (Ni-SGPA) catalyst material deposited on a substrate and the second electrode that includes an anode and a reference electrode. The electrolyte includes H2SO4. The cell also includes an electric power supply for applying a pulsed voltage between the foil and a reference electrode and counter electrode. Another hydrogen-producing cell includes a first and second electrode. The first electrode includes a cathode that includes a nickel single-atom graphdiyne porphyrin analogue (Ni-SGPA) catalyst material deposited on a substrate and the second electrode includes an anode and a reference electrode. The electrolyte includes KOH. The cell also includes an electric power supply for applying a pulsed voltage between the foil and a reference electrode and counter electrode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part application of International Patent Application No. PCT/NO2025/050151, which application is incorporated by reference in its entirety.

STATEMENT REWARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

One or more of the inventors listed in this application invented the subject matter disclosed in Bifunctional Ni Single Atoms on Graphdiyne-Porphyrin Analogs Enabling Highly Energy-Efficient Pulsed Water Splitting (“the publication”). Non-inventor co-authors of the publication are not inventors of the subject matter disclosed therein and worked under the direction of a joint inventor. Non-inventor co-authors of the publication contributed to the publication by performing manuscript review or characterization assistance.

BACKGROUND

This invention is related to reducing the environmental difficulties caused by excessive fossil fuel use, such as global warming and climate change.

Global interest in hydrogen production via water splitting powered by renewable energy has grown markedly, driven by the urgent need to address carbon emissions and climate change. With its high energy density of 142 MJ/kg, hydrogen is increasingly viewed as a viable source to replace fossil fuels. This shift toward a hydrogen-based economy represents a promising solution to the growing environmental challenges. However, as noted by the U.S. Department of Energy, hydrogen production costs remain high, with industrial-scale hydrogen production via electrocatalysis currently priced at around $7 per kg. The goal is to reduce this cost to approximately $1 per kg by 2036, making it a more viable and accessible clean energy source.

Efficient hydrogen production faces significant challenges due to high energy consumption, sluggish kinetics, and the reliance on rare and expensive metal-based catalysts, such as gold and platinum, which not only elevate costs but also suffer from performance limitations in water splitting. These catalysts typically have unevenly distributed active sites on their surfaces, edges, and crystal planes, leading to reduced active site density. A promising approach to overcome these issues is the downsizing of catalysts to single atoms, which can increase active site density and maximize atom utilization. The use of single atoms of non-precious metals offers a cost-effective alternative for green hydrogen production. While the use of single atoms of non-precious metals offers a cost-effective alternative for green hydrogen production, their practical performance is often constrained by the inherent drawbacks of traditional electrocatalysis methods, which apply a constant voltage throughout the process. These limitations, namely high energy consumption and bubble-induced mass diffusion barriers, have motivated alternative approaches, such as those demonstrated by Pan et al., Mater. Chem. Front. 1021, 5, pages 4596-4603, where crystalline porphyrin-based graphdiyne was employed under constant voltage, or in WO2015/05280, where a homogeneous Ni-porphyrin complex was explored as a photocatalytic hydrogen carrier capable of releasing hydrogen.

The present invention is aimed at addressing the problems presented above, mitigating these critical concerns related to climate change by providing an efficient solution for hydrogen generation by water splitting, thus constituting a new, efficient, and cost-effective solution for producing hydrogen. The objects of the invention being obtained as defined in the accompanying claims.

According to the present invention a novel nickel single-atom catalyst supported on graphdiyne porphyrin analogues (Ni-SGPA) is utilized. The graphdiyne structure, with its two acetylenic linkages between aromatic rings, enhances the conductivity of the otherwise non-conductive porphyrin analogues due to its π-conjugated system. The Ni-SGPA catalyst maximizes atom utilization by incorporating single atoms of nickel, a non-precious metal, into the structure. Ni-SGPA demonstrated exceptional performance under water-splitting conditions. In addition, pulse electrocatalysis is applied, which applies voltage in controlled pulses, and addresses the issues with the constant state electrocatalysis by improving reaction kinetics and reducing energy consumption.

When paired with an optimized pulsed electrocatalysis profile using a H2SO4 electrolyte, further featuring a 3-second pulse period, 50% duty cycle, and −1.1V vs Reversible Hydrogen Electrode (RHE), the Ni-SGPA produced hydrogen with a 12% higher current density compared to the constant voltage method, while maintaining equivalent hydrogen flow rates and reducing energy consumption by 48%. This remarkable achievement is attributed to the synergistic effects of the Ni-SGPA's innovative design, the optimized pulse profile, and an efficient mechanism for bubble removal and enhanced mass transfer. As will be seen below corresponding results may be achieved with a KOH (potassium hydroxide) electrolyte.

At the core of this high performance lies the synergetic combination of Ni-SGPA with the pulsed electrocatalysis. While the Ni-SGPA catalyst provides additional and isolated active sites for the chemical reaction, the pulsed electrocatalysis alleviates the key process limitations such as mass diffusion and bubble removal via optimized pulsed profiles. Thus, these two aspects go hand in hand to improve the gas production and are the key ingredients of this invention.

While the Ni-SGPA material per se will be known to the person skilled in the art, an advantageous production method, can be used which corresponds to the one described in Zubair Masaud et al: “Cu Single Atoms Supported on Crystalline Graphdiyne Porphyrin Analogs with Dual Active Sites for Enhanced C₂ Product Formation”, Department of Microsystems, University of South-Eastern Norway, Horten 3184, Norway. According to the present invention, the Cu atom in the Masaud et al article above can be exchanged with a Ni single atom in the crystalline graphdiyne porphyrin analog, providing a Ni-SGPA, be used as a catalyst for producing hydrogen. Thus the process can be described as follows:

Step	Reagents & conditions	Purpose	Yield
1. Adler-Longo	2.5 g 4-((TMS)-	Forms Ni-	83%
condensation	ethynyl)benzaldehyde + 1.78 g	porphyrin
	NiCl2 in 60 mL propionic acid, N2,	monomer
	80° C., 0.5 h → add 1.3 g pyrrole,	(Product 1) with
	reflux 2.5 h	TMS-protected
		terminal groups
2. Desilylation	1 g Product 1 in 100 mL THF, +6	Frees terminal	71%
	mL TBAF, N2, reflux, overnight, 25° C.;	alkynes for
	work-up with CH2Cl2/H2O →	coupling
	Product 2
3. Glaser-Hay	200 mg NiCl2, 100 mL pyridine +	Builds TT-	84.5%
polymerisation	100 mL acetone, N2, 70° C.;	conjugated
	syringe-pump in 200 mg Product 2	graphdiyne
	in 50 mL acetone, reflux 48 h →	sheet
	dialysis (H2O) → freeze-dry	embedding
		isolated Ni—N4
		sites (Product 3 =
		Ni-SGPA)

This way nickel is trapped in square-planar Ni-N₄ pockets during Step 1, and subsequent Glaser coupling rigidly locks each atom into the extended graphdiyne lattice, preventing aggregation.

The present invention thus provides a solution where hydrogen is produced using Ni-SGPA deposited on a substrate as a working electrode in a process for producing hydrogen. More specifically the invention is preferably related to a pulsed voltage applied over the Ni-SGPA resulting in pulsed electrocatalysis conditions for producing hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below with reference to the accompanying drawings, illustrating the invention by way of examples.

FIG. 1 illustrates the chemical structure of the Ni-SGPA.

FIG. 2 illustrates a sketch of the hydrogen production cell.

FIG. 3(a) illustrates the performance of Ni-SGPA including peak current density at different voltages at constant and pulsed voltages.

FIG. 3(b) illustrates the performance of Ni-SGPA including hydrogen production at constant and pulsed voltages.

FIG. 3(c) illustrates the performance of Ni-SGPA including energy consumption and savings, at constant and pulsed voltages.

DETAILED DESCRIPTION

FIG. 1 illustrates the structure of the Ni-SGPA. The substrate used for the deposition of Ni-SGPA will preferably be a Cu foil, but other Cu substrates may also be contemplated, such as foam, block, or rod. Depending on the use and availability other materials than Cu may also be used as a substrate, such as nickel and carbon supports.

FIG. 2 illustrates an example of a production cell 1 where the Ni-SGPA electrode 3 is positioned in a suitable electrolyte 2, and where a pulsed voltage is applied through a potentiostat 5 connected to the first Ni-SGPA electrode 3, second electrode 4, and third, reference electrode 7. The electrolyte 2 will preferably be a 0.5M H₂SO₄ or 1M KOH electrolyte, as further discussed below.

The cell will thus be a three-electrode system, the voltage is measured between two electrodes. The details are as follows:

• • 1. Working Electrode 3, constituting the Ni-SGPA electrode, where the reaction of interest takes place. The potential at the working electrode is what you want to measure and control.
  • 2. Reference Electrode 7, often an Ag/AgCl or a calomel electrode provides a stable and known reference potential. The potential of the working electrode is measured relative to the reference electrode.
  • 3. Counter Electrode 4, also known as the auxiliary. The counter electrode is used to complete the electrical circuit by providing the current that flows to or from the working electrode.

The voltage or potential is measured between the working electrode 3 and the reference electrode 7. The counter electrode 4 is used to pass current, but its potential is not measured. It serves to ensure that the system can drive the required current while the reference electrode maintains a stable potential. In summary, while there are three electrodes in the system, the voltage (potential) is measured only between the working electrode and the reference electrode.

The applied voltage between the working electrode 3 and the reference electrode 7 will preferably be about −0.8V for KOH or −1.1V for H2SO4, but possibly in the range of −0.4 to −1.3V, vs RHE. In the illustrated example the cell is connected to a potentiostat 5 which is the source of the pulsed voltage. Thus, the cathode side electrode 3 is the Ni-SGPA electrode and the anode or counter side electrode 4 is a graphite rod. The reference electrode 7 is preferably Ag/AgCl (3M KCl) electrode. The electrolyte 2 is preferably a 0.5M concentration of H₂SO₄ or 1 M KOH. During the application of the voltage pulses the Ni-SGPA acts as a catalyst producing hydrogen by water-splitting reaction on the cathode side of the electrochemical cell. This will result in the production of gas droplets on the Ni-SGPA cathode 3.

FIG. 3 shows the performance of the Ni-SGPA in water-splitting conditions. FIG. 3 (a) shows the peak current densities (mA/cm²) achieved at various potentials ranging from −0.4V to −1.3V vs RHE, where the upper curve marked with triangles represents pulsed voltage and the lower marked with circles represent constant voltage. Here, it can be seen that the Ni-SGPA under the effect of pulsed voltages generates 12% higher current densities than its constant voltage counterpart. Similarly, FIG. 3(b) shows that despite using half the energy the Ni-SGPA under pulsed voltage (triangles) generates the same amount of hydrogen, measured in gas flow rate (sccm) as Ni-SGPA under constant voltage (circles). Finally, FIG. 3 (c) displays a comparison in energy consumption in mJ between pulsed (triangles) and constant (circles) Ni-SGPA electrocatalysis. It can be seen that the energy saving (stars) with Ni-SGPA under pulsed electrocatalysis results in about 48% less energy consumption.

The discussion above is based on the use of an H₂SO₄ electrolyte. According to an alternative embodiment KOH (Potassium hydroxide) is used as an electrolyte using the same Ni-SGPA material deposited on a substrate as indicated above. In that case the electrolyte concentration is between 0.1 M and 10 M KOH, preferably 1M KOH. In this case the applied voltage may be in the range of −0.4V and −1.3V vs RHE, preferably −0.8V vs RHE, with a pulse width in the range of 1-15 s, preferably 3 s, and with a duty cycle with a range of 10% to 90%, preferably 50%. In general the pulse frequency may be in the range of 1/20 to 1 Hz and preferably about ⅕ Hz, depending on pulse width and other conditions.

To summarize, the present invention relates to a cell for producing hydrogen using a water-splitting process, as well as a compound and method related to this. The hydrogen-producing cell comprises a first and second electrode, wherein the first electrode is constituted by a cathode including a Ni-SGPA material deposited on a substrate and the second electrode may be constituted by a graphite rod or similar, for example, carbon in the form of graphite or its alloys, platinum, or silver, acting as an anode. The electrodes are positioned in an electrolyte comprising H₂SO₄ or KOH and the cell also comprises an electric power supply for applying a pulsed voltage between the foil and a graphite electrode.

The substrate may be constituted preferably by a Cu material, or possibly a Ni or C-based material, and may be realized in the form of a foil, foam, or rod.

The applied voltage will in a preferred embodiment be in the range of −0.4V and −1.3V, preferably −0.8V vs RHE for KOH or −1.1 vs RHE for H2SO4, and with a pulse width in the range of 1-15 s and with a duty cycle in the range of 10-90%, preferably 50%.

As an alternative, the voltage may be in the range of −0.4V and −1.3 V, preferably −0.8V vs RHE for KOH or −1.1 vs RHE for H2SO4, with a pulse width in the range of 1-15 s and with a duty cycle in the range of 10-90%, preferably 50%.

The electrolyte will be in the range of 0.1 to 2 M, and preferably a 0.5M concentration of H₂SO₄ Or 0.1 to 10 M, and preferably a 1 M concentration of KOH.

The compound for producing hydrogen according to the invention is thus a catalyst constituted by the Ni-SGPA provided on a substrate, the substrate preferably being Cu.

The method for producing hydrogen based on the cell described above thus involves the steps of applying a pulsed voltages over the electrodes with a pulse voltage, pulse width and frequencies as described above. The voltage is measured between the cathode and the reference electrode while the reference and anode electrodes may be at the same potential.

Claims

1. A hydrogen-producing cell comprising a first and second electrode, wherein the first electrode is constituted by a cathode constituted by a nickel single-atom graphdiyne porphyrin analogue (Ni-SGPA) catalyst material deposited on a substrate and the second electrode constituting an anode and a reference electrode, the electrolyte comprising H2SO4, the cell also comprising an electric power supply for applying a pulsed voltage between the foil and a reference electrode and counter electrode.

2. The hydrogen-producing cell according to claim 1, wherein the substrate is constituted by a Cu, Ni or C-based material, preferably a Cu-based material.

3. The hydrogen-producing cell according to claim 2, wherein the substrate is made from at least one of a foil, foam, or rod.

4. The hydrogen-producing cell according to claim 1, wherein the second electrode is constituted by a carbon-based material in the form of graphite or its alloys, or platinum or silver.

5. The hydrogen-producing cell according to claim 1, wherein the reference electrode is an Ag/AgCl (3M KCl) or a calomel electrode.

6. The hydrogen-producing cell according to claim 1, wherein the voltage is in the range of −0.4V and −1.3V, and preferably −0.8V, vs RHE and with a pulse width in the range of 1-15 s and with a duty cycle in the range of 10 to 90%, preferably 50%.

7. The hydrogen-producing cell according to claim 1, wherein the voltage is in the range of −0.4V and −1.3V, preferably −0.8V vs RHE and with with a pulse width in the range of 1-15 s, preferably 3 s, and with a duty cycle in the range of 10 to 90%, preferably 50%.

8. The hydrogen-producing cell according to claim 1, wherein the electrolyte comprises 0.1 to 2 M, preferably 0.5M, H2SO4.

9. An electrode for producing hydrogen comprising a substrate, the substrate bearing a coating layer of Ni-SGPA.

10. The electrode according to claim 9, wherein the substrate is made from Cu, Ni or C-based material.

11. The electrode according to claim 9, wherein the substrate is made from at least one of a foil, foam, or rod.

12. A method for producing hydrogen by applying a pulsed voltage of a chosen magnitude over a cathode Ni-SGPA electrode and an anode in an electrolyte of H2SO4.

13. The method according to claim 12, wherein the voltage is in the range of −0.8V and −1.3V, preferably −1.1V, vs RHE, and with a pulse width in the range of 1-6 s and with a duty cycle of 50%.

14. The method Method according to claim 12, wherein the voltage is in the range of −0.8V and −1.3 V, preferably −1.1V, vs RHE and with a pulse width in the range of 2-6 s, preferably 3 s, and with a duty cycle of 50%.

15. The method according to claim 12, wherein the electrolyte comprises 0.1 to 2M, preferably 0.5M, H2SO4.

16. The method according to claim 12, wherein the voltage is measured between the cathode and a reference electrode, the reference electrode being essentially at the same potential as the counter electrode.

17. A hydrogen-producing cell comprising a first and second electrode, wherein the first electrode is constituted by a cathode constituted by a nickel single-atom graphdiyne porphyrin analogue (Ni-SGPA) catalyst material deposited on a substrate and the second electrode constituting an anode and a reference electrode, the electrolyte comprising KOH, the cell also comprising an electric power supply for applying a pulsed voltage between the foil and a reference electrode and counter electrode.

18. The hydrogen-producing cell according to claim 17, wherein the substrate is constituted by a Cu, Ni or C-based material, preferably a Cu-based material.

19. The hydrogen-producing cell according to claim 18, wherein the substrate is made from at least one of a foil, foam, or rod.

20. The hydrogen-producing cell according to claim 17, wherein the second electrode is constituted by a carbon-based material in the form of graphite or its alloys, or platinum or silver.

21. The hydrogen-producing cell according to claim 17, wherein the reference electrode is an Ag/AgCl (3M KCl) or a calomel electrode.

22. The hydrogen-producing cell according to claim 17, wherein the voltage is in the range of −0.4V and −1.3V, and preferably −0.8V, vs RHE and with a pulse width in the range of 1-15 s, preferably 3 s, and with a duty cycle in the range of 10-90%, preferably 50%.

23. The hydrogen-producing cell according to claim 17, wherein the electrolyte comprises 0.1 to 10 M, preferably 1M, KOH.

24. A method for producing hydrogen by applying a pulsed voltage of a chosen magnitude over a cathode Ni-SGPA electrode and an anode in an electrolyte of KOH.

25. The method according to claim 24, wherein the electrolyte comprises 0.1 to 10M, preferably 1M, KOH.