Description:FIELD OF INVENTION
The present invention relates to the field of electrochemistry. More specifically, the invention relates to an electrode for anion exchange membrane (AEM) electrolyzer which can act as both hydrogen and oxygen production electrocatalyst, more particularly to an electrodeposited electrode and a preparation method thereof.
BACKGROUND OF THE INVENTION
Green hydrogen production through water electrolysis using renewable energy sources is crucial for creating a sustainable and affordable approach. Anion exchange membrane water electrolysis (AEMWE) is seen as a viable energy conversion technology that could replace fossil fuel-dependent systems. Anion exchange membrane (AEM) electrolysis has the benefit of merging the strengths of alkaline water electrolysis (AWE) and polymer electrolyte membrane (PEM) electrolysis, with the latter relying on costly platinum-group metals like platinum, iridium, and ruthenium for catalytic activity.
CN114525539 discloses a maquinol sulfide electrocatalyst with high catalytic activity and stability, a preparation method of the maquinol sulfide electrocatalyst and application of the maquinol sulfide electrocatalyst in electrolyzed water. The sulfide electrocatalyst is prepared by the following steps: firstly, electrically depositing a zinc oxide nanorod on the surface of foamed nickel, then electrically depositing a cobalt nanolayer on the nanorod, then etching the zinc oxide nanorod in a strong alkaline solution to form a cobalt nanotube, then soaking the cobalt nanotube in an iron-containing solution to adsorb enough iron ions on the surface, washing and drying, and finally, preparing the sulfide electrocatalyst. And finally, soaking in an organic sulfur compound to adsorb enough sulfydryl, and calcining in a tubular furnace under the protection of inert gas.
A. Dolati, et al., the effect of cysteine on electrodeposition of gold nanoparticle discloses a study evaluating effects of cysteine additive on the properties of electrodeposited gold nanoparticles. The study concludes that cysteine is an appropriate agent to refine gold nanoparticles due to increase of nucleation sites and improves kinetic parameters leading to eight times increase in oxygen reduction in KOH solution in comparison to the conventional gold deposits.
WO2009046181 discloses electrodeposited nanogranular chromium composites or chromium alloys on brass substrate. The said chromium alloy comprises chromium, carbon, nitrogen, oxygen and sulfur. In one of the embodiments, the said chromium alloy contains other metals like Ni and Co. The electrodeposited chromium composites/alloys have both TEM crystalline and XRD amorphous structure. Bivalent sulfur compounds e.g., L-Cysteine are used as sulfur source during the electrodeposition and concentration of bivalent sulfur source is responsible for TEM crystalline and XRD amorphous structure of the electrodeposited chromium composites/alloys. The concentration of bivalent sulfur source ranges from about 0.0001 M to less than about 0.01 M.
However, the electrode for anion exchange membrane (AEM) electrolyzer known in the art are not effective in water splitting at lower basic pH and requires higher concentration of KOH to perform optimally. Thus, there exists an unmet need for an electrode for AEM electrolyzer that can effectively carry out water splitting reaction at lower basic pH or lower concentration of KOH.
OBJECTIVE OF THE INVENTION
A principal objective of the present invention is to provide an electrode for anion exchange membrane (AEM) electrolyzer.
Another objective of the present invention is to provide an electrode comprising a Ni foam coated with Ni-Co-S (NCS-LC) nano-chunks.
Yet another objective of the present invention is to provide a method for preparation of electrode for anion exchange membrane (AEM) electrolyzer.
SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.
In an aspect of the present invention, there is provided an electrode for anion exchange membrane (AEM) electrolyzer comprising Ni foam substrate coated with nano-chunks of nickel, cobalt, sulfur.
In another aspect of the present invention, there is provided a method of preparing an electrode for anion exchange membrane (AEM) electrolyzer comprising: preparing nickel foam pieces having 1mm thickness, 1cm length, and 1cm width, followed by cleaning the nickel foam pieces by subjecting the pieces to ultrasonication in the mixture of ethanol and acetone of 1:1 volume for 5 minutes to 25 minutes to obtain Ni foam substrate and coating of Ni-Co-S (NCS-LC) nano-chunks on the Ni foam substrate by subjecting the foam substrate to electrodeposition. Drying the Ni foam substrate deposited with Ni-Co-S (NCS-LC) nano-chunks at room temperature to obtain the electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates the XRD spectra of Ni-Co-S (NCS-LC) pristine bi-functional electrocatalyst.
Figure 2 illustrates the FESEM images of Ni-Co-S (NCS-LC) deposited on Ni foam.
Figure 3 illustrates the EDS elemental mapping of Ni-Co-S (NCS-LC) deposited on Ni foam.
Figure 4 illustrates the XPS spectra of the Ni-Co-S (NCS-LC) composites: comparison of Ni 2p peaks (a) pristine bi-functional electrodes, and electrodes after stability test for more than 1000 hours; (b) anode i. e. OER electrode (NCS-LC-AST) and (c) cathode i. e. HER electrode (NCS-LC-CST).
Figure 5 illustrates the XPS spectra of the Ni-Co-S (NCS-LC) composites: comparison of Co 2p peaks (a) pristine bi-functional electrodes, and electrodes after stability test for more than 1000 hours; (b) anode i. e. OER electrode (NCS-LC-AST) and (c) cathode i. e. HER electrode (NCS-LC-CST).
Figure 6 illustrates the XPS spectra of the Ni-Co-S (NCS-LC) composites: comparison of S 2p peaks (a) pristine bi-functional electrodes, and electrodes after stability test for more than 1000 hours; (b) anode i. e. OER electrode (NCS-LC-AST) and (c) cathode i. e. HER electrode (NCS-LC-CST).
Figure 7 Chronoamperometry analysis of (a) electrodeposited NCS-LC, (b) Hydrothermally grown NCS (NCS-HT) and (c) comparison with commercial catalyst.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated culture blend, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.
The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.
The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.
Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.
The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.
The term “optionally,” as used in the present disclosure, means that a feature or element described as ‘optional’ within the context of the invention is not required for the invention to function as claimed. It indicates that the presence or absence of the described feature or element does not alter the fundamental operation or scope of the invention, and its inclusion or exclusion may be determined based on the specific requirements or preferences of a practitioner skilled in the art or the particular application in question.
As used herein, the term “Catalyst” refers to a substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction.
As used herein, the term “electrocatalyst” refers to a surface where chemical energy is electrochemically. converted into electrical energy in fuel cells.
As used herein, the term “AEM” refers to Anion Exchange Membrane used in the electrolyzer, and during the process of electrolysis, where anions will move from cathode side to anode side to initiate the Hydrogen generation reaction.
As used herein, the term “electrodeposition” refers to a process of coating a thin layer of one metal on top of a different metal to modify its surface properties, by donating electrons to the ions in a solution.
As used herein, the term “ultrasonication” refers to a physical treatment to disperse, disrupt, emulsify, extract, and/or homogenise biomass via the application of ultrasonic frequencies.
In an embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer comprising Ni foam substrate coated with nano-chunks of nickel, cobalt, sulfur.
In another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the sulfur is sourced from L-Cysteine.
In yet another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the nickel is sourced from nickel chloride hexahydrate (NiCl2.6H2O).
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the cobalt is sourced from cobalt (II) chloride hexahydrate (CoCl2.6H2O).
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the said electrode is used as anode and cathode with a membrane in AEM.
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the said electrode is used as anode and cathode with a diaphragm in AEM.
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the nickel foam is of 1mm thickness.
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the electrode has both amorphous and crystalline structure and has three strong Ni planes (111), (200), (220) XRD peaks centered at 44.2°, 51.63° and 76.2° along with less intense peak towards the low angle relates to the designed electrocatalyst.
In still another embodiment, the present invention provides an electrode for anion exchange membrane (AEM) electrolyzer, wherein the electrode is functional at a lower basic pH electrolyte solution, wherein the electrolyte solution is having a KOH concentration of < 5 wt.%.
In still another embodiment, the present invention provides a method of preparing an electrode for anion exchange membrane (AEM) electrolyzer comprising a) preparing nickel foam substrate for electrodeposition; b) electrodeposition of Ni-Co-S (NCS-LC) nano-chunks on the prepared nickel foam; and c) drying the Ni foam substrate deposited with Ni-Co-S (NCS-LC) nano-chunks to obtain the electrode for anion exchange membrane (AEM) electrolyzer.
In still another embodiment, the present invention provides a method of preparing an electrode for anion exchange membrane (AEM) electrolyzer comprising preparing nickel foam substrate comprises cleaning the nickel foam substrate by subjecting to an ultrasonication in a mixture containing equal volumes of ethanol and acetone for 5 to 25 minutes, preferably for 15 minutes.
In still another embodiment, the present invention provides a method of preparing an electrode for anion exchange membrane (AEM) electrolyzer wherein the electrodeposition comprises: a) preparing a solution comprising 10mL of 50mM Nickel source, 10 ml of 100mM of Cobalt source and 10 ml of 10mM L-Cysteine as sulfur source; b) configuring an electrodeposition set-up, wherein the prepared nickel foam is configured as working electrode, Ag/AgCl electrode with saturated KCl is configured as reference electrode, and platinum wire is configured as counter electrode; c) operating the electrodeposition set-up at a reduction potential of -0.7V to -0.9V, against Ag/AgCl for 40 to 80 minutes.
In still another embodiment, the present invention provides a method of preparing an electrode for anion exchange membrane (AEM) electrolyzer wherein the electrodeposition set-up is operated at a reduction potential of -0.8V against Ag/AgCl for 60 minutes.
EXAMPLES
Example 1 - Evaluation of designed electrode
The prepared electrode is tested in electrolyzer set up (electrolyzer is an assembly of two stainless steel plates acts as positive and negative terminal to the applied voltage, plated are fixed by nut and bolt, wherein the electrolyte is continuously circulated by a peristatic pump, electrolyte inlet through cathode and the outlet will be used to collect the H2 gas, nanoparticles deposited on Ni foams by electrodeposition technique are used as anode and cathode) with a membrane or a diaphragm which help to transport the active hydroxyl ion species (OH- ions) and the results are reliable and can be scaled up. Operational parameter like applied voltage of the electrolyzer is maintained at 1.8 V which is less for AEM at room temperature to design the electroactive modified surface properties enriched nanocatalyst material for H2 generation.
Example 2 - Corrosion prevention
Alkaline water electrocatalyst used 30 wt.% KOH solution, which is highly basic with greater pH value can corrode the electrocatalyst material and leaching of the active material may happen which will affect the stability of the electrocatalyst. Here the modified Ni foam electrocatalyst was designed where it is active at a very low KOH concentration i.e. less than 5 wt.% with activity comparable to the high pH electrolyte solution.
Example 3 - Determination of structural parameters
The structural parameters of the prepared electrode were studied using X-Ray diffraction (XRD) patterns, and X-photoelectron spectroscopy (XPS). Figure 1 demonstrates the diffraction pattern of Ni-Co-S (NCS-LC) /NF, which shows three strong Ni planes (111), (200), (220) peaks centred at 44.2°, 51.63° and 76.2°. Three small intensity peaks at 15.98o, 31.92o and 39.19o were also observed, which corresponds to the XRD peaks of the designed materials. As the full width half maxima (FWHM) for these peaks is less which confirms the size of the particles is in nanometre range. The result clearly revealed the smaller size of the designed material along with the presence of both amorphous and crystalline structure of the prepared electrode.
The structure further confirmed by SEM analysis. Figure 2 shows the surface of Ni foam which is uniformly decorated by nano-chunks of Ni-Co-S (NCS-LC). The figure showed a proper growth of the catalyst. The bare Ni foam shows a smooth surface but after deposition roughness in the surface of Ni foam is clearly visible. This structure shows the large surface area by which active sites for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can be exposed, and electrolyte ions can also access. Also revealed that the surface of Ni foam which is uniformly adorned by nano-chunks of Ni-Co-S (NCS-LC) and is extremely compact in nature.
Figure 4, 5 and 6 demonstrates the X-Ray photoelectron spectra (XPS) in the Ni2p, Co2p and S2p region, respectively. The two peaks located at 865.9eV and 871.8eV correspond to the Ni 2p3/2 and Ni 2p1/2 respectively. Similarly for Co 2p doublet is found at 800.4 and 781.5eV correspond to Co 2p3/2 and Co 2p1/2 respectively. It is showing the coexistence of Co2+ and Co3+ both. For S 2p peaks binding energy located at 163.9eV revealed the M-S bonding along with an intense peak at high binding energy at 168.5 eV corresponds to the bonding of sulphur with oxygen which will also control the charge transfer because of the difference in the surrounding electronegativity.
From the XPS analysis the Ni-Co-S (NCS-LC)/NF surface contains Ni2+, Ni3+, Co2+, Co3+ and M-S bond. The results are accordant to the reported oxides and sulphides of Ni-Co precursor. Coordination between the transition metal and sulphur giving good stability for long time and as S ligand is like OH- ions in term of electronegativity so the transfer of electrons is favourable here. We also studied the XPS analysis of evaluated electrocatalyst after it’s stability test (chronoamperometry) for more than 1000 hrs and presented in figure 4, 5 and 6 as NCS-LC-AST for evaluated anode and NCS-LC-CST is for evaluated cathode. The XPS results clearly reveals that, there is a shift in the binding energy for all Ni2p, Co2p and S2p peaks corresponds to the change in the oxidation states and charge moieties in the process of electrolysis after long duration evaluation.
Example 4 - Determination of composition of Ni-Co-S (NCS-LC)/NF
Composition study of Ni-Co-S (NCS-LC) /NF is conducted by EDS analysis (Figure 3). The elements Ni, Co, S and O were detected, and the elemental ratio of Ni and Co is found to be 1:2.
Example 5 - Evaluation of water splitting reaction
Water splitting reaction evaluation to generate hydrogen and oxygen is carried out in a prototype single cell electrolyzer (Reported in a beaker set-up).
For comparison, L-cystine is used in hydrothermal process to synthesis the Ni-Co-S (NCS-HT) electrocatalyst to compare the electrochemical analysis results with the designed electrodes. Simultaneously, the commercially available electrocatalyst was compared.
Figure 7 demonstrates that the kinetic of water splitting is significantly higher in prototype electrolyzer for the designed electrode compared to the hydrothermally grown samples and commercially available ones. The designed Ni-Co-S (NCS-LC) electrodeposited electrode is showed substantially better activity compared to the others because of the presence of abundant active site in the process fabrication. We have compared the activity of the designed electrodes with the commercially available once and presented in figure 7C. It is clear from the result that the activity of the in-house developed electrode is substantially better compared to the commercial once.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the disclosure, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense. The disclosure has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the disclosure provided herein. This disclosure is intended to include all such modifications and alterations in so far as they come within the scope of the present disclosure. These and other modifications of the preferred embodiments as well as other embodiments of the disclosure will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
Finally, to the extent necessary to understand the present disclosure, all publications, patents, and patent applications mentioned herein are expressly incorporated by reference therein to the same extent as though each were individually so incorporated. , Claims:1. An electrode for anion exchange membrane (AEM) electrolyzer, said electrode comprising a nickel foam substrate coated with a nano-chunks of nickel, cobalt, and sulfur (Ni-Co-S).
2. The electrode as claimed in claim 1, wherein the sulfur is sourced from L-Cysteine.
3. The electrode as claimed in claim 1, wherein the nickel is sourced from nickel chloride hexahydrate (NiCl2.6H2O) and the cobalt is sourced from cobalt (II) chloride hexahydrate (CoCl2.6H2O).
4. The electrode as claimed in claim 1, wherein the nickel foam is of 1mm thickness.
5. The electrode as claimed in claim 1, wherein the electrode has both amorphous and crystalline structure and has three strong Ni planes (111), (200), (220) XRD peaks centered at 44.2°, 51.63° and 76.2°.
6. The electrode as claimed in claim 1, wherein the electrode is functional at a lower basic pH electrolyte solution, wherein the electrolyte solution is having a KOH concentration of < 5 wt.%.
7. A method of preparing an electrode for anion exchange membrane (AEM) electrolyzer comprising:
a) preparing nickel foam substrate for electrodeposition;
b) electrodeposition of Ni-Co-S (NCS-LC) nano-chunks on the prepared nickel foam; and
c) drying the Ni foam substrate deposited with Ni-Co-S (NCS-LC) nano-chunks to obtain the electrode for anion exchange membrane (AEM) electrolyzer.
8. The method as claimed in claim 7, wherein the preparing nickel foam substrate comprises cleaning the nickel foam substrate by subjecting to an ultrasonication in a mixture containing equal volumes of ethanol and acetone for 5 to 25 minutes, preferably for 15 minutes.
9. The method as claimed in claim 7, wherein the electrodeposition comprises:
a) preparing a solution comprising 10mL of 50mM Nickel source, 10 ml of 100mM of Cobalt source and 10 ml of 10mM L-Cysteine as sulfur source;
b) configuring an electrodeposition set-up, wherein the prepared nickel foam is configured as working electrode, Ag/AgCl electrode with saturated KCl is configured as reference electrode, and platinum wire is configured as counter electrode; and
c) operating the electrodeposition set-up at a reduction potential of -0.7V to -0.9V, against Ag/AgCl for 40 to 80 minutes.
10. The method as claimed in claim 9, wherein the electrodeposition set-up is operated at a reduction potential of -0.8V against Ag/AgCl for 60 minutes.