HER Catalysts Research Articles

Synergistic influence of multivalent Ruδ+ on a CeOx nanocatalyst for self-powered efficient electrochemical water splitting

A Ruδ+-fabricated CeOx based multicomponent electrocatalyst with engineered surface-electronic states acts as an efficient trifunctional ORR, OER, and HER catalyst towards zinc–air battery powered overall water splitting.

Ni–Mo nanostructure alloys as effective electrocatalysts for green hydrogen production in an acidic medium

Ni–4Mo demonstrating its promise as a durable and efficient HER catalyst in acidic media.

Going from Pt to PGM-free Catalysts: Effects of Ink Compositions on PEM Water Electrolysis.

The commercialisation of PEM water electrolysis is still hindered by the necessity of using noble metals that are rare, expensive and therefore unsustainable. To replace the benchmark HER catalyst Pt with more abundant materials, promising non-noble catalysts need to be identified and optimal electrode preparation and electrolysis conditions need to be transferred between catalyst materials to reveal their full potential under industrially relevant conditions. This study investigates the optimal ink composition for spray-coating the cathode regarding the effects on electrode structure, performance and catalyst layer composition. The ratio of catalyst to binder and carbon support was varied as well as the specific carbon material and the resulting electrodes were analysed via polarisation curves, electrochemical impedance spectroscopy, X-ray photo-electron spectroscopy and scanning electron microscopy for three different catalysts. These results show that ink compositions with a catalyst : carbon : binder ratio of 3:1:1 using Carbon Vulcan give the highest performance. Interestingly, resulting trends concerning electrochemical behaviour and electrode structure observed with different characterisation techniques can be transferred between Pt catalysts and non-noble transition metal chalcogenide materials. Boosting the performance via ink optimisation is much more pronounced for the non-noble catalysts, narrowing the gap to competing with noble standard Pt materials.

Enhanced Catalytic Activity of CuO@CuS Core-Shell Structure for Highly Efficient HER Application.

Using electrocatalytic water reduction to produce hydrogen fuel offers significant potential for clean energy, yet its large-scale adoption depends on developing cost-effective, non-precious, and efficient catalysts to replace expensive Pt-based state-of-the-art HER catalysts. The catalytic HER performance of an active catalyst largely depends on the available catalytic active sites, conductivity, and intrinsic electrochemical kinetics, all of which can be altered by incorporating a heteroatom into the active catalyst structure. Herein, we synthesized a unique nitrogen-doped CuO@CuS (NCOS) core-shell-structured catalyst through a facile hydrothermal process followed by an efficacious nitrogenation process, and its electrochemical performance for the HER was systematically analyzed. The NCOS core-shell-structured catalyst exhibits a reduced overpotential (55 mV) and Tafel slope (107 mV dec-1) compared to the pure CuS (CS; 179 mV and 201 mV dec-1) catalyst at a current density of 10 mA cm-2. Moreover, the NCOS core-shell-structured catalyst demonstrates excellent endurance for up to 50 h of chronopotentiometric testing at a driving current density rate of 10 and 100 mA cm-2. This excellent catalytic HER activity is a result of an increased electron transfer rate and a greater number of accessible active sites, attributed to a change in structural properties and the high electronic conductivity aroused from nitrogen incorporation, as evidenced from the TOF and EIS curve analyses.

Atmosphere-driven oriental regulation of Ru valence for boosting alkaline water electrolysis

Modulating the electronic characteristics of nanomaterials has been key to advancing sustainable energy technologies. In this study, we controlled the Ru electronic properties of NiRuOx by varying the calcination atmospheres (Air and Argon), resulting in two distinct electrocatalysts: NiRuOx-O2 with Ru4+ species and NiRuOx-Ar with Ru0 species as the main component. We established the relationship between the valence of Ru and its HER and OER catalytic activity as NiRuOx for example. Specifically, NiRuOx-Ar with metallic Ru demonstrates better alkaline HER activity with a smaller overpotential (94 mV) at 100 mA cm−2 than NiRuOx-O2 with Ru4+ due to the reduced Ru0 superiority towards H*. Conversely, NiRuOx-O2 shows superior alkaline OER performance with only 275 mV overpotential at 100 mA cm−2 compared with that of NiRuOx-Ar (383 mV) due to Ru4+ receiving electrons from Ni species and reduced Ru–O covalence. The NiRuOx-O2//NiRuOx-Ar electrolyzer in 1 M KOH achieves 10 mA cm−2 at 1.475 V with 100 h durability, surpassing the RuO2//Pt/C cell (1.516 V). Revealing the correlation between Ru valence and activity offers important insights for the rational design of Ru-based catalysts for HER and OER.

Porous Amorphous-Crystalline Heterostructured CoNiP Nanowire Arrays for Enhanced Hydrogen Evolution Performance under Acid-Base Conditions.

A novel porous amorphous-crystalline heterostructured CoNiP nanowire arrays ((a-c)CoNiP/CC) is presented. TEM observations and compositional calculations revealed ≈14.5% of the amorphous regions (a-CoNiP) are interleaved in the crystalline regions (c-(Co3.6Ni0.4)P4), forming massive amorphous-crystalline heterogenous interfaces composed of the same elements. Only 38 and 64mV overpotentials for the (a-c)CoNiP/CC catalyst are required to reach the current density of -10mAcm2 in acid and alkaline electrolyte, respectively, which is very close to the overpotentials (35 and 55mV) of the commercial Pt/C HER catalyst. The theoretical calculation revealed that the (a-c)CoNiP/CC has a completely different enhancement mechanism of HER reaction in acid-base electrolytes. In particular, due to the natural corrosion resistance of the amorphous interface, the HER performance of this catalyst under the high current density condition is much better than that of the Pt/C catalyst either in acidic or in alkaline, suggesting its prospect for commercial applications.

Polysaccharide derived Ru/Ni HER catalysts for long-run anion exchange membrane water electrolysis

Developing economical, efficient and stable hydrogen evolution catalysts is of great significance for the development of renewable hydrogen energy. In this work, Ru/Ni catalysts were prepared using polysacharide as carbon carrier by a novel preparation strategy. Thus the prepared catalysts have a unique porous carbon-supported structure which has sufficient surface area and high stability. The results of HRTEM, XRD and XPS tests proved that Ru/Ni catalysts containing RuO2, Ru and NiO have been successfully prepared. The Ru/Ni-100, which was prepared in a optimal condition, has excellent hydrogen evolution reaction (HER) catalytic activity with an overpotential of 119 mV at a current density of 50 mA/cm2. In addition, the actual anion exchange membrane water electrolysis cell (AEMWE) loaded with Ru/Ni-100 as HER catalysts has excellent performance, with a cell voltage of 1.84 V at 1 A/cm2 and long-term stability over >1500 h of continuous water electrolysis at 1 A/cm2. These findings indicate that Ru/Ni catalysts have great application potential in practical large-scale hydrogen production.

Plasma-Structured Molybdenum Oxycarbides Enabling Ultrastable Acidic Hydrogen Evolution up to 10 a cm-2

Fabricating electrocatalysts capable of stable operation at high current densities is crucial for the industrial proton exchange membrane water electrolysis. However, current catalysts suffer from high overpotentials and rapid degradation when working in acid electrolytes at high current densities. Despite these advantages, critical challenges still exist in designing efficient catalysts for HER in acidic electrolytes at high current densities: 1) Poor long-term stability. The corrosive environment of strong acids, combined with the heat and mechanical stresses from hydrogen (H2) bubble generation at high current densities, severely challenges the stability of existing catalysts, including those noble metal-based ones. Catalysts with both excellent thermodynamic stability and robust physical adhesion to substrates are required to ensure long-term stability under these harsh conditions. 2) High overpotential at large current densities. At high current densities, high activation energy is required to drive HER because of the rapidly consumed H3O+ near the catalyst surface and the blocked active sites by the high-level H2 bubble coverage at catalyst surfaces, leading to increased overpotential and reduced energy efficiency.Existing transition metal-based catalysts generally exhibit optimal activities only at low current densities (1-100 mA cm−2) with limited stability, making their operation in acidic electrolytes at industrial-level current densities (> 3 A cm−2) quite challenging. Non-equilibrium plasmas, characterized by highly energetic reactive species in a far-from-equilibrium state and the capability to operate at low temperatures, offer distinct advantages in the development and fabrication of innovative materials. The existence of non-equilibrium plasmas can significantly influence nucleation and crystal growth processes in material synthesis, facilitating thermodynamically unfavorable reactions that are difficult or impossible to achieve using conventional equilibrium thermal methods.In this paper, we report the in-situ growth of vertically standing nanoedge-enriched molybdenum oxycarbide nanosheets (MoOxCy) through plasma-enhanced chemical vapor deposition (PECVD) based on earth-abundant salts (i.e., MoO3 and NaCl) as precursors to achieve ultrahigh-throughput acidic electrocatalytic hydrogen evolution at high current densities up to 10 A cm-2. The plasma-structured nanoedge-enriched MoOxCy catalysts offer the following benefits toward HER: 1) Significantly improved long-term stability of catalysts because of the non-equilibrium plasma-engineered structures, which are kinetically unfavorable to obtain through conventional equilibrium thermal methods; 2) Strong localized electric field near the ultrasharp edges of the catalysts, enabling fast diffusion of H3O+ from the electrolyte to catalyst surface; 3) Efficient hydrogen bubble detachment from the nanoedge-enriched structure with high roughness, maintaining continuous exposure of catalytic sites to the surrounding electrolyte. Benefiting from the unique plasma-induced morphology and chemical composition, the MoOxCy exhibits outstanding HER performance with a low overpotential (η) of 415 mV at an ultrahigh current density (j) of up to 10 A cm-2 for 1,000 h in 0.5 M H2SO4. This performance leads to an ultrahigh H2 throughput of 4,477.4 L cm-2, substantially outperforming the state-of-the-art transition metal- and even noble metal-based catalysts. This work paves new avenues for the development of high-efficiency catalysts for practical industrial applications in electrocatalytic hydrogen evolution.

The Effect of Different Membrane Types on the Activity and Stability of Nickel-Based Catalysts for Water Splitting

Due to the increasing annual rise in carbon dioxide levels from burning fossil fuels for energy, which is accelerating climate change, countries are moving away from fossil fuels and turning to hydrogen as a sustainable, renewable alternative. Hydrogen offers more than twice as much energy per mass compared to other fuels and can be produced renewably through water electrolysis using wind or solar energy. Electrolysis requires electrocatalysts that control the half-reactions of water splitting at a low enough overpotential, i.e. the difference between the theoretical potential and the actual potential at which these reactions take place.Platinum group metals (PGMs) are the favored electrocatalysts due to their efficiency, but they are expensive and only available in small quantities in the earth's crust. Efforts are therefore being made to replace them with more abundant and less expensive transition metals such as nickel. Nickel is an excellent OER catalyst under alkaline conditions and has recently also shown promise as a HER catalyst. Such catalysts are used in zero-gap electrolyzers, where the separators between the anode and cathode are membranes, however, recently it has been shown that these separators can be improved to limit gas crossover and metal cross-contamination. 1In this work we present how different types of exchange membranes affect activity and stability of nickel-based electrocatalysts. It is well known that different metals that form alloys with nickel affect its electrochemistry, such as the effect of iron on nickel that increases the activity of the OER. The experiments were conducted in a gas diffusion electrode (GDE) with which we achieve higher current densities than standard laboratory scale methods mainly the rotating disc electrode. Another benefit of GDE is that it can utilize a membrane, so it closely resembles membrane electrode assemblies (MEAs), which are the benchmark used for testing catalyst for industrial application. With these results we wish to stress the importance of using the right separator with respect to the activity and stability of nickel-based electrocatalysts.2,3(1) Cohen, L. A.; Weimer, M. S.; Yim, K.; Jin, J.; Fraga Alvarez, D. V.; Dameron, A. A.; Capuano, C. B.; Ouimet, R. J.; Fortiner, S.; Esposito, D. V. How Low Can You Go? Nanoscale Membranes for Efficient Water Electrolysis. ACS Energy Lett. 2024, 1624–1632. https://doi.org/10.1021/acsenergylett.4c00170.(2) Hales, N.; Schmidt, T. J.; Fabbri, E. Reversible and Irreversible Transformations of Ni-Based Electrocatalysts during the Oxygen Evolution Reaction. Curr. Opin. Electrochem. 2023, 38, 101231. https://doi.org/10.1016/j.coelec.2023.101231.(3) Ehelebe, K.; Schmitt, N.; Sievers, G.; Jensen, A. W.; Hrnjić, A.; Collantes Jiménez, P.; Kaiser, P.; Geuß, M.; Ku, Y.-P.; Jovanovič, P.; Mayrhofer, K. J. J.; Etzold, B.; Hodnik, N.; Escudero-Escribano, M.; Arenz, M.; Cherevko, S. Benchmarking Fuel Cell Electrocatalysts Using Gas Diffusion Electrodes: Inter-Lab Comparison and Best Practices. ACS Energy Lett. 2022, 7 (2), 816–826. https://doi.org/10.1021/acsenergylett.1c02659.

First-Principles Studies on the Design of Tungsten-Based Platinum Electrocatalyst for Hydrogen Evolution Reaction in Alkaline Environment

Hydrogen production has gained prominence as a clean and sustainable energy source, with water electrolysis emerging as a key method for generating hydrogen gas. Platinum (Pt), although extensively used as a cathode electrocatalyst in both acidic and alkaline media electrolyzers due to its moderate hydrogen binding energy, utilization in the Anion Exchange Membrane (AEM) system suffers from low catalytic activity. OH and H2O adsorption energy must be strong enough for facile water dissociation while H binding must be ideal to prevent H desorption from being the bottleneck. In this work, first-principles calculations were used to design Tungsten (W)-based Pt catalyst to effectively control the adsorption energies and aim for a superior alkaline HER catalyst compared to the bulk Pt catalyst. Owing to the weak OH and H2O binding energy on the conventional Pt slab, two methodologies were employed to precisely control adsorption strength of each intermediate. Nanoscale engineering of catalysts, modelled as Pt55 icosahedral nanocluster, was employed where the interaction of all the adsorbates with the surface was increased, lowering the activation barrier for water decomposition. Another approach is through monolayer deposition of Pt on the W simulated as Pt/W(110) slab where the heterogeneous surface induced strain effect and ligand effect. With the discrepancy of the crystal structures of two metals, strain effect was seen more dominant, where adsorbate-induced strain effect also played a significant role in fine-tuning the the adsorption energies of each adsorbate in a favorable direction. Lastly, pursuing the synergistic effect of both methods, W@Pt core-shell nanoparticle structure was formed which did not show enhanced catalytic activity. Since such fine-tuning of adsorption energies of varied intermediates is normally done by engineering a complex heterogeneous surface to execute for bifunctional active sites, this work will provide insights to control the adsorption energies with a simple metal monolayer surface. Figure 1

Boosting Hydrogen Production: Non-Noble Metal Catalysts Optimize Electrodes in Anion Exchange Membrane Water Electrolysis

As the world transitions to renewable energy sources, efficient energy storage is crucial for managing power fluctuations and decarbonize crucial high temperature processes. Achieving grid balance and optimizing renewable energy capacity requires innovative solutions. One promising option is the conversion of electrical energy into hydrogen through Anion Exchange Membrane Water Electrolysis (AEM-WE).AEM-WE combines high hydrogen production rates per electrode area and little production site footprint of Proton Exchange Membrane Water Electrolysis (PEM-WE) with cost-effectiveness of non-noble electrode materials utilized in Alkaline Water Electrolysis (A-WE). To further optimize AEM-WE, it is essential to improve hydrogen production while reducing material costs. This can be achieved through innovative approaches to electrocatalyst and electrode design. However, developing cost-effective catalysts that combine superior efficiency and robustness in aqueous environments, ideally in alkaline conditions, remains a big challenge. In this work, two electrode preparation approaches are investigated. For the anodic OER a corrosion synthesis is been developed to form highly active NiFe-layered double hydroxide (LDH) structures on nickel non-woven porous transport layers (PTL). A highly active cell can be combined with a cathodic HER catalyst, prepared by electrochemical deposition Ni-S on a stainless steel non-woven PTL.In single cell AEM water electrolysis using 1 M KOH-solution utilizing the prepared NiFe-LDH anode and Pt/C cathode, 2.7 A/cm² at 2 V were achieved, surpassing commercially available powder catalysts like NiFe-oxide. Comparative analysis of Ni-S cathode with NiFe-LDH, integrated into a membrane electrode assembly demonstrated superior AEM-WE performance, outperforming the mentioned platinum on carbon catalysts. Electrochemical impedance spectra indicated higher charge transfer activity of Ni-S cathode compared to Pt/C. Importantly, the electrodes prepared in this study exhibited stability under accelerated electrochemical stress tests for 1000 cycles.These approaches provide a simple, inexpensive, scalable and therefore industry-relevant fabrication method with improved active areas and excellent catalytic activity during AEM water electrolysis. Figure 1

Bipolar Hydrogen Production from Electrocatalytic Oxidative Dehydrogenation of Biorenewable Furfural in Membrane-Less Electrolyzers

Water electrolysis has been considered a green process for hydrogen production. Conventional electrolysis is limited by the sluggish anodic oxygen evolution reaction (OER), leading to high energy input. In addition, the temporal spatial coupling of the production of H2 and O2 can cause issues associated with safety, economic feasibility, and system flexibility. Herein, we reported our work on replacing OER with an electrocatalytic oxidative dehydrogenation (EOD) of biomass-derived furfural for bipolar H2 production (from both cathode and anode) at low electrolytic cell voltages and high current densities. Experimental and DFT studies suggested a reasonable barrier for C-H dissociation on Cu surface, mainly through the diol intermediate, with the potential-dependent competition with Cannizzaro reaction. We revealed that EOD on metallic Cu surface was linked to an autocatalytic Cu oxides reduction by aldehydes along with H2 evolution. The EOD kinetics and durability was further enhanced by a porous CuAg catalyst prepared by a galvanic replacement method. We engineered a bipolar H2 production system using membrane-electrode assembly-based flow cells to facilitate mass transport, achieving a combined faradaic efficiency (FE) of ~200% to H2 and the maximum H2 partial current density of 248 and 390 mA/cm2 at cell voltages of 0.4 V and 0.6 V, respectively. We further studied other CuM (M= Pt, Pd, Au) bimetallic catalysts for EOD reaction, and found that dispersing Pt into Cu (CuPt) exhibited a unique synergistic effect for furfural EOD possibly via efficient C-H cleavage on Cu and favorable furfural binding on Pt. The CuPt anode-based flow electrolyzer has achieved a higher current density of 498 mA/cm2 at a low cell voltage of 0.6 V and FE of >80% to H2. Inexpensive dialysis membranes and non-noble metal HER catalysts are possibly used for bipolar H2 production, which provides an alternative approach for distributed manufacturing of green hydrogen and carbon chemicals in the future.

Synthesis Framework for Designing PtPdCoNiMn High-Entropy Alloy: A Stable Electrocatalyst for Enhanced Alkaline Hydrogen Evolution Reaction.

High entropy alloys (HEAs) are an emerging class of advanced materials characterized by their multifunctionality and potential to replace commercial catalysts in electrocatalytic water splitting. The synergy among the various alloyed elements in HEAs makes them particularly promising for applications in electrocatalysis. However, preparation of HEA via bottom-up approaches by avoiding the formation of mono, di, and tri metallic alloys in the nanoscale is challenging. This aspect is addressed, in this study by exploring the logical selection of solvents, reducing agents, and capping agents, along with their relative fractions, in the solvothermal synthesis of the HEA comprising platinum-palladium-cobalt-nickel-manganese (PtPdCoNiMn). It is established that the reducing capabilities of both the solvent and reducing agent are crucial for the reduction of each metal to form a single-phase HEA. The synthesized HEA (20 wt.%)/functionalized carbon (FC) demonstrates excellent performance as an HER catalyst, exhibiting a low overpotential of 48.7mV at -10 mA cm-2 in an alkaline electrolyte. This performance is characterized by high reaction kinetics and stability at elevated current densities. Furthermore, the catalyst shows impressive performance in both simulated and actual seawater. This development reduces the reliance on platinum while enhancing the long-term durability and catalytic efficiency of the electrocatalyst.

In Situ Growth of MoN on Nickel Foam for Highly Efficient Hydrogen Evolution in Alkaline Solution.

Highly efficient, stable, and low-cost hydrogen evolution catalysts are urgently required for water electrolysis. Herein, a method for in situ growth of medium-nitrogen nanosheet MoN catalysts with a large electrochemical surface area on nickel foam (NF) is proposed. The results show that the morphology of the as-prepared catalysts greatly depends on the nitrogen sources and nitridation temperature. The MoN/NF catalyst nitride at 700 °C using melamine as a nitrogen source exhibits a spindle-like morphology consisting of stacked nanosheets, which is conducive to exposing more active sites, thereby increasing the catalyst activity. The N atoms in MoN could adjust the chemical environment of the metal by changing the density of the d-band electron state, which further improves the HER performance. Benefiting from the regulation of Mo charge distribution and exposure to more active sites through N doping and morphological control, the MoN/NF catalyst exhibits superior HER performance with an overpotential of 70 mV at a current density of 10 mA·cm-2, a Tafel slope of 44.3 mV dec-1, and an Rct of 1.83 Ω, indicating high HER catalytic activity, fast kinetics, and excellent conductivity. Theoretical calculations reveal that among the (002), (202), and (200) planes of MoN, the (202) plane exhibits the lowest value of |ΔGH*| (0.47 eV), which is close to that of Pt(111) (0.14 eV). More importantly, MoN(202) also has the smallest work function of 3.58 eV, indicating an enhanced capability to offer electrons. This work develops a strategy to design high-performance and low-cost transition-metal nitride HER catalysts.

Regulating local atomic environment of Fe3O4 to promote anion exchange membrane based alkaline seawater electrolysis

Designing efficient and durable HER electrocatalysts for seawater splitting to resist the corrosive seawater is crucial for continuous seawater electrolysis technology. Herein, a self-supported Fe3O4 electrode with P doping and O vacancy (P-Fe3O4-x) was constructed as an efficient and stable HER catalyst under alkaline seawater. A set of characterization reveals that P doping and O vacancy can effectively regulate the local atomic environment of Fe3O4, optimizing the hydrogen adsorption/desorption of Fe site on P-Fe3O4-x. Moreover, the unique electron-rich local atomic environment of Fe site decreases the adsorption energy of Cl- at the Fe site, remarkably enhance the corrosion-resistance of P-Fe3O4-x. As expected, the obtained P-Fe3O4-x displays high activity (367 mV at 3 A cm−2) and outstanding 1000 h stability in alkaline seawater solution. Besides, the AEM electrolyzer using P-Fe3O4-x as cathode achieves seawater electrolysis of 1.0 A cm−2 at 1.97 V and operates stably for 100 h at the high current density of 1.0 A cm−2.

Bimetallic Sulfur-Doped Nickel-Cobalt Selenides as Efficient Bifunctional Electrocatalysts for the Complete Decomposition of Water.

The creation and enhancement of non-precious metal bifunctional catalysts with superior stability and stabilizing activity is necessary to achieve water splitting in alkaline media. The paper presents a method for preparing nickel-cobalt bimetallic selenides (NiCo-Sex/CF) using a combination of hydrothermal and high-temperature selenization techniques. NiCo-Sex/CF shows great potential as a catalyst for water separation. The catalyst's electronic structure and active centre can be modified by double doping with sulfur and selenium, resulting in increased selectivity and activity under varying reaction conditions. This method also offers the benefits of a simple preparation process and applicability to a wide range of catalytic reactions. Experimental results demonstrate that an overpotential of 194 mV produces a current density of 10 mA cm-2 when using this electrocatalyst as an OER catalyst. When used as a HER catalyst, the electrocatalyst required an overpotential of only 76 mV to generate a current density of 10 mA cm-2.Furthermore, a voltage of 1.5 V can drive the overall decomposition of water to achieve a current density of 10 mA cm-2. This study highlights the potential of sulfur-selenide double-doped catalysts for both scientific research and practical applications.

Low Zn-doped Co3O4 nanorods for enhanced hydrogen evolution reaction

Transition metal oxides have been identified as the best potential candidates to replace Pt-based HER catalysts. But they are still limited by the high HER overpotential, due to the undesirable adsorption/desorption of surface hydrogen. In this work, Zn with low concentrations were incorporated into the tetrahedral Co2+ sites of Co3O4 by hydrothermal and subsequent annealing treatment. They exhibit excellent HER performance. Particularly, when the Zn content in Co3O4 is 6.3 at%, an overpotential of 79.2 mV at the current density of 10 mA cm−2 was obtained in alkaline medium, which significantly better than pure Co3O4 catalyst (196.3 mV). Moreover, the current density of the Zn-doped Co3O4 catalyst can maintained 93 % after 10 h and 80 % after 20 h. DFT calculations reveal that the ΔGH* of Zn-doped Co3O4 (0.827 eV) is smaller and closer to zero than pure Co3O4 (1.023 eV). This work provides a deep insight into the rational design of low-level metal-doped cobalt oxide-based electrocatalysts.

Direct Formation of Nifep Catalytic Films on Anion Exchange Membrane As Efficient HER Catalyst for Water Electrolysis Device

Anion exchange membrane water electrolysis (AEMWE) is advantageous in terms of device cost, compared with proton exchange membrane water electrolysis, because non-noble metal-based catalyst in alkaline condition is applicable.1 In AEMWE device, the membrane electrode assemblies (MEAs) plays an important role on the cell performance and stability.2 And the MEAs fabricated by (catalyst-coated-membrane) CCM cathode and (catalyst-coated-substrate) CCS anode is proved to be appropriate configuration.3 In the conventional way, the CCM cathode employs an ionomer/binder to combine the catalyst layer and AEM together, which however suffers the problem of degradation, thus limiting the life time of the device.2 We have reported an electroless deposition process that allows Ni-based metal to be deposited directly on AEM surface, which opens the possibility to fabricate CCM without ionomer/binder.4 In this work, NiFeP films (1 cm × 1 cm in area, ~3 μm in thickness) is electrolessly deposited on Tokuyama A-201 AEM as HER catalyst in room temperature AEMWE device. Electroless deposition method forms NiFeP films on AEM surface without binder, thus avoiding the disadvantage of degradation of the catalyst due to the ionomer/binder. The successfully deposited NiFeP catalyst exhibits outstanding HER performance by delivering -500 mA/cm2 at overpotential of -0.50 V in 1.0 M K2CO3 at room temperature. Furthermore, the NiFeP catalyst shows a good stability by delivering -500 mA/cm2 for at least 20 h without obvious potential loss. The outstanding HER performance of NiFeP should originates from the increased number of active sites caused by porous structure of the interface and the enhanced intrinsic activity caused by the well-tuned electronic structure. A series of characterization would be presented in terms of composition, morphology, phase and electron transfer behavior of the NiFeP films. Our work is hoped to give a new insight of fabrication of MEAs to achieve better performance of AEMWE devices. References R. R. Raja Sulaiman, W. Y. Wong, and K. S. Loh, Intl J of Energy Research, 46, 2241–2276 (2022).Y. Leng et al., J. Am. Chem. Soc., 134, 9054–9057 (2012).H. Ito et al., J Appl Electrochem, 48, 305–316 (2018).T. Fujimura, M. Kunimoto, Y. Fukunaka, H. Ito, and T. Homma, Electrochemistry, 89, 192–196 (2021).

Towards High-Performance AEM Water Electrolyzers: Transitioning from PGM to Low-PGM and PGM-Free Electrocatalysts

Hydrogen, known for its high gravimetric energy density and low environmental impact, is widely regarded as a promising low-carbon energy carrier. The production of hydrogen via water electrolysis offers a valuable opportunity to efficiently utilize renewable energy resources – both as a storage and transport medium and to produce hydrogen that is a crucial feedstock for multiple industrial and manufacturing applications. Among various water electrolysis technologies, anion exchange membrane water electrolyzers (AEMWEs) are notable for their distinct and advantageous features. Their alkaline operational environment significantly reduces corrosion, allow for the possibility to use catalysts and cell component materials that are earth abundant and cost effective. Moreover, the use of anion exchange membranes (AEMs) as the electrolyte and zero-gap design enhance operational efficiency and hydrogen production rates compared to traditional alkaline electrolyzers. These benefits position AEMWEs as a compelling solution for efficient, cost-effective large-scale hydrogen production.To date, the development of lower-cost AEMWEs has been hindered by several challenges. A critical issue is the activity and durability of catalysts, particularly those that are platinum group metal (PGM)-free. This leads many researchers and electrolyzer manufacturers to lean on PGM catalysts at both the anode and cathode. These catalysts, while effective, significantly increase the cost and complexity of the system, posing a barrier to widespread adoption and commercialization of AEMEL technology in the burgeoning hydrogen economy. PGM-free anodes have been demonstrated for the AEMWE, but there have been fewer PGM-free options for the cathode.This study assessed the performance and durability of various low-PGM and PGM-free electrocatalysts for the oxygen evolution (OER) and hydrogen evolution (HER) reactions. We focused on Lanthanum Strontium Cobalt (LSC), Nickel Ferrite (NiFeOx), and Lead Ruthenate (PbRuOx) for the OER at the anode, and Nickel Molybdenum (NiMo), Nickel Rhenium (NiRe), and a low-PGM PtNi for the HER at the cathode. Furthermore, the performance of the NiMo HER catalyst was enhanced by optimizing the physical properties of both the catalyst powder and the electrodes. These experimental results offer crucial insights into developing PGM-free AEM water electrolyzer systems, marking a progressive step towards their commercial feasibility.

Understanding the Degradation Mechanism for NiMo Composite and Effect of Ionomer on the Activity Towards HER

Hydrogen is an essential commodity for achieving cleaner and greener energy.1,2 Due to its high gravimetric energy density, hydrogen is favored as a carbon-neutral fuel.2,3 Moreover, the electrochemical accessibility of hydrogen evolution and oxidation reactions enable hydrogen to be used as a reversible fuel, as in hydrogen battery anodes and unitized reversible fuel cells.4,5 Platinum group metals (PGMs) are excellent catalyst for hydrogen chemistry, as they exhibit negligible activation barrier for HER and HOR, but they are costly and the upstream processes for mining and purification are unsustainable.6 A promising alternative to PGM catalysts would be nonprecious transition metal alloys/composites in form of nanoparticles. These materials are more readily available and lower in cost. Nonetheless, non-precious catalysts developed to date have never met the benchmarks set by PGMs in terms of catalytic activity and stability.Our lab is continuing a long-running effort to develop and improve nickel-molybdenum (Ni–Mo) composites, which stand as one of the strongest candidates for non-PGM HER and the HOR. In prior work, we developed a method to synthesize Ni–Mo nanoparticles supported on oxidized carbon, which increases catalyst dispersion and significantly reduces losses due to interfacial resistivity.7 The catalyst composite has a core@shell structure, where in the core is mainly nickel-rich alloy and the shell is primarily molybdenum-rich oxide.Furthermore, DFT calculations suggest the addition of Mo in the catalyst subsurface weakens hydrogen binding to surface Ni sites, thus increasing the overall activity toward HER/HOR.8 In ongoing work to further develop Ni–Mo/C composites, we are focusing on catalyst degradation under storage and operating conditions. To examine catalyst durability upon extended storage, we measured activity toward hydrogen evolution progressively for a single batch of catalyst powdered retained at room temperature in an aerobic environment over 850 hours. We observed a monotonic decrease in catalytic activity culminating in a >90% decrease in activity. Post-mortem analysis via XRD showed the increased peak intensities corresponding to NiO and MoO3. We further observed that the catalyst remains active over extended periods when stored under a dry, oxygen-free atmosphere. Finally, exposing the degraded catalyst to thermal reduction increased catalytic activity. Together, these results strongly suggest aerobic oxidation as the primary degradation mechanism under shelf-storage, with straightforward mitigations steps readily available by excluding air and water. This finding further suggests that oxide component of the synthesized catalyst is not an active site for hydrogen chemistry, although we speculate that some surface oxide is beneficial for enhancing the rate of water dissociation.9 We also studied the impact of the ionomer chemistry on the catalytic activity of Ni–Mo composites for alkaline anion exchange membrane (AEM) electrolyzer applications. Surprisingly, we observed an ~80% reduction in catalytic activity for Ni–Mo composites formulated into thin film HER catalysts using poly(aryl piperidinium) (PAP) carbonate AEM ionomers relative to control samples based on Na-exchanged Nafion ionomer binders. Further work showed this result was specific to the carbonate form of the ionomer, as HER activity was fully recovered when we used halide forms of the PAP ionomer. Work is ongoing to establish the physicochemical basis of this poisoning effect.Based on these findings, we developed functional AEM electrolyzer assemblies with IrOx anodes and Ni–Mo/C cathodes, where the cathode composition was formulated based on our best results from RDE studies. These MEAs yielded electrolyzer performance properties that were indistinguishable from MEAs we tested using Pt–Ru/C cathodes that were otherwise identical in composition.8 This leads us to conclude that advanced Ni–Mo/C catalyst composites can indeed achieve performance parity with PGM catalysts on the basis of initial catalytic activity, whereas significant work remains to characterize durability under extended operating conditions.