Reference Hydrogen Electrode Research Articles

Performance Optimization of Alkaline Water Electrolysis Via Catalyst Morphology Tuning and Novel Cell Design

Hydrogen is a basic energy carrier for numerous valuable industrial products. Green hydrogen produced using renewable electricity and water electrolysis is pivotal in advancing a decarbonized sustainable energy ecosystem. Two primary electrolysis technologies, alkaline water electrolysis (AWE) and polymer electrolyte membrane water electrolysis (PEMWE), have demonstrated a viable commercial perspective. AWE is particularly well-suited for large-scale deployment, especially at the gigawatt scale, due to low capital cost and long lifetime. [1]. The performance of AWE is largely determined by the effectiveness of nickel-based oxygen evolution reaction (OER) catalysts and PGM-based or PGM-free hydrogen evolution reaction (HER) catalysts. To enhance the catalyst activity and cell performance, we meticulously control morphology and chemical composition of the catalysts. Cell testing was conducted in cells of various active areas (5, 25, and 50cm2) to demonstrate the result consistency and scalability. An innovative cell design, incorporating a reference hydrogen electrode in both cathode and anode, enabled the real-time acquisition of half-cell polarization curves during tests. This configuration proved valuable information to identify performance limitations in the single cells, thus guiding effective cell design and optimization. Furthermore, a cell comprising Ni-based anode and PGM cathode demonstrated remarkable stability.1. Schalenbach, Aleksandar R. Zeradjanin, Olga Kasian, Serhiy Cherevko, and Karl J.J. Mayrhofer, Int. J. Electrochem. Sci., 1173–1226 (2018).

Low-temperature fabrication of morphology-controllable Cu2O for electrochemical CO2 reduction

Cu2O has been successfully synthesized in different morphologies/sizes (nanoparticles and octahedrons) via a low-temperature chemical reduction method. Trapping metal ions in an ice cube and letting them slowly melt in a reducing agent solution is the simplest way to control the nanostructure. Enhancement of charge transfer and transportation of ions by Cu2O nanoparticles was shown by cyclic voltammetry and electrochemical impedance spectroscopy measurements. In addition, nanoparticles exhibited higher current densities, the lowest onset potential, and the Tafel slope than others. The Cu2O electrocatalyst (nanoparticles) demonstrated the Faraday efficiencies (FEs) of CO, CH4, and C2H6 up to 11.90, 76.61, and 1.87%, respectively, at −0.30 V versus reference hydrogen electrode, which was relatively higher FEs than other morphologies/sizes. It is mainly attributed to nano-sized, more active sites and oxygen vacancy. In addition, it demonstrated stability over 11 h without any decay of current density. The mechanism related to morphology tuning and electrochemical CO2 reduction reaction was explained. This work provides a possible way to fabricate the different morphologies/sizes of Cu2O at low-temperature chemical reduction methods for obtaining the CO, CH4, and C2H6 products from CO2

Influence of the modification of chlorophyll-rich extracts on the hydrogen evolution reaction of rGO-based electrocatalysts

The great efforts to develop alternative electrocatalysts for efficient hydrogen evolution reaction (HER) applications through environmentally friendly synthesis still need to be completed. We explore a green route using spinach extract to simultaneously reduce and functionalize graphene oxide (GO). A spinach extract, rich in green reducing agents and chlorophyll, was obtained and modified by saponification and demetallation to yield Chln-H2 and further used to reduce and functionalize GO in a one-step procedure. The resulting RGO/Chln-H2 electrocatalyst was evaluated on the HER by Lineal Sweep Voltammetry (LSV), achieving a current density of −34.84 mA/cm2 starting its activation from an onset potential of −0.68 V vs reference hydrogen electrode (RHE). The effect of saponification and demetallation produces a new metal-free alternative catalyst with increased current density seven times, boosting hydrogen production performance.

Poisoning Mechanism of the CO and H2S Mixture on the Anode of Polymer Electrolyte Membrane Fuel Cell

AbstractDespite the coexistence of CO and H2S in reformed hydrogen, studies on the interaction between impurities are lacking. In this study, the co‐poisoning effect of CO and H2S on a polymer electrolyte membrane fuel cell (PEMFC) is systematically investigated using a hydrogen reference electrode inserted into a membrane electrode assembly (MEA). Notably, when CO and H2S are present simultaneously, the poisoning rate is accelerated and is higher than the simple sum of the poisoning by the individual gases, suggesting a complex synergic effect between the two gases. This phenomenon can be attributed to the potential‐dependent behavior of H2S poisoning, whereas CO poisoning remains independent of the potential but depends on the total poisoning time. Therefore, the potential of the anode rises over time due to the time‐dependent CO poisoning, which accelerates the potential‐dependent H2S poisoning. As a result, the cell voltage decreases more rapidly in the CO and H2S mixture.

Electron Spin Selective Iridium Electrocatalysts for the Oxygen Evolution Reaction.

Highly efficient electrocatalysts for water electrolysis are crucial to the widespread commercialization of the technology and an important step forward toward a sustainable energy future. In this study, an alternative method for boosting the electrocatalytic activity toward the oxygen evolution reaction (OER) of a well-known electrocatalyst (iridium) is presented. Iridium nanoparticles (2.1 ± 0.2 nm in diameter) functionalized with chiral molecules were found to markedly enhance the activity of the OER when compared to unfunctionalized and achiral functionalized iridium nanoparticles. At a potential of 1.55 V vs Reference Hydrogen Electrode (RHE), chiral functionalized iridium nanoparticles exhibited an average 85% enhancement in activity with respect to unfunctionalized iridium nanoparticles compared to an average 13% enhancement for the achiral functionalized iridium nanoparticle. This activity enhancement is attributed to a spin-selective electron transfer mechanism taking place on the chiral functionalized catalysts, a characteristic induced by the chirality of the ligand. This alternative path for the OER drastically reduces the production of hydrogen peroxide, which was confirmed via a colorimetric method.

HER Kinetics of Pt and Ni in Alkaline Medium at Elevated Temperatures (25-200 ºC) and Pressures (1-50 bar)

The hydrogen evolution reaction (HER) in alkaline medium is of great importance for the economic production of sustainable hydrogen. Nevertheless, the origin of the sluggish reaction kinetics observed in alkaline compared to acidic environment, remains a point of debate. [1-5] In order to promote understanding, and to extend the discussion at conditions closer to industrial operation, we have undertaken a systematic determination of the HER kinetics on Pt and Ni within a broad range of temperatures (25-200 ⁰C) and pressures (1-50 bar) in alkaline environment using 1 M or 10 M aqueous KOH as electrolyte.At present, the study of HER at high temperatures and pressures (HTP) is limited by the interim stability and lifetime of the available reference electrodes [6, 7]. We have overcome this limitation by employing a novel design for a Palladium hydride (PdH) and a reversible hydrogen (RHE) reference electrodes that enable facile and stable utilization at HTP [8]. A constant electrochemically driven supply of H2 on the PdH surface ensures preservation of the mixed (α+β)-phase in the PdH layer and thereby stable potential at HTP conditions for prolonged periods. Furthermore, the potential of the PdH reference electrode has been calibrated as a function of temperature and pressure with respect to the reversible hydrogen electrode (RHE). The potential of the PdH electrode in the mixed (α+β)-phase is ~55 mV vs. the RHE at 25 ⁰C, 1 bar, and observed to be independent of temperature and pressure.As shown in Figure 1, the HER kinetics are faster on Pt relative to Ni and become more sluggish on both metal surfaces upon increasing KOH concentration from 1 to 10 M at 25 ⁰C, 1 bar. A more pronounced thermal activation is observed in 10 M versus 1 M KOH though, resulting in a reversal of the pH trend at 100 ⁰C, 1 bar. References Sheng, M. Myint, J. G. Chen, Y. Yan, Energy Environ. Sci., 6, 1509–1512 (2013).Ledezma-Yanez, W. D. Z. Wallace, P. Sebastián-Pascual, V. Climent, J. M. Feliu, M. T. M. Koper, Nature Energy, 2, 17031–17037 (2017).Rossmeisl, K. Chan, E. Skúlason, M. E. Björketun, V. Tripkovic, Catalysis Today, 262, 36–40 (2016).Subbaraman, D. Tripkovic, D. Strmcnik, K. Chang, M. Uchimura, A. P. Paulikas, V. Stamenkovic, N. M. Markovic, Science, 334, 1256–1261 (2011).Liu, J. Li, L. Jiao, H. T. T. Doan, Z. Liu, Z. Zhao, Y. Huang, K. M. Abraham, S. Mukerjee, Qingying Jia, J. Am. Chem. Soc., 141, 3232−3239 (2019).H. Miles, G. Kissel, P. W. T. Lu, S. Srinivasan, J. Electrochem. Soc., 123, 332–336 (1976).J. Appleby, G. Crepy, J. Jacquelin, Int. J. Hydrog. Energy, 3, 21–37 (1978).P. Leuaa, C. Chatzichristodoulou, J. Electrochem. Soc., 169, 054534 (2022). Figure 1: (a) HER overpotential versus current density (normalized by the electrochemically active surface area) on Pt and Ni at 25 ⁰C, 1 bar, in 1 and 10 M KOH, and (b) temperature evolution of the HER overpotential at 10 mA/cm2 (normalized by the electrochemically active surface area) for Pt and Ni at 25-100 ⁰C, 1 bar, in 1 and 10 M KOH. Figure 1

Electrochemical Activation of NiFe2O4 for the Oxygen Evolution Reaction in Alkaline Media

Electrochemical H2 production via low temperature H2O electrolysis is a promising strategy to facilitate decarbonization across sectors;1 however, current high-performing proton exchange membrane (PEM) electrolyzers require the use of expensive and rare platinum-group metals (PGMs) for catalysts and hardware, limiting scale up feasibility.2 More recently, anion exchange membrane (AEM) electrolyzers have emerged as an alternative strategy, combining the zero-gap approach employed by PEM with operation in an alkaline environment where many non-PGMs are thermodynamically stable.3 In fact, oxides of first row transition metals including Ni, Fe, and Co have been proposed as promising anode catalyst alternatives to IrO2 in AEM electrolyzers.4–7 However, these materials suffer from high overpotentials (> 300 mV @ 10 mA/cm2)8 and kinetic improvements are needed to facilitate the deployment of this technology.Ni-Fe oxides have gained particular attention due to their high ex-situ activities and typically low material criticality compared to IrO2 or other non-PGMs such as Co.9 Ni and Fe are known to have a synergistic effect, with trace amounts of Fe in Ni catalysts leading to increased OER activity.10 However, the mechanism behind the improved performance and the optimal Fe content is heavily debated in the literature;11 for example, this activity enhancement has been attributed to increased electrical conductivity with increasing Fe content,10 stabilization of the Ni4+ state,12 and a shift of the Ni (II/III) redox couple.13 Furthermore, these studies have evaluated Ni-Fe catalysts in their metallic or oxy(hydroxide) forms, although device-level conditioning may passivate near-surfaces and minimize performance differences between catalysts with difference ex-situ oxide content.14 Uncovering how Fe content changes over time-on-stream for nanoparticle oxides and correlating this to changes in activity is needed to facilitate optimization of these materials at the device level. To this end, this work evaluated the stability of NiFe2O4 nanoparticles (30 nm) in alkaline environments, correlating changes in Fe composition to changes in activity. All tests were performed in a rotating disc electrode cell with Au working electrode (0.193 cm2), Au counter electrode, and reversible hydrogen reference electrode. Tests were performed in 0.1 M NaOH electrolyte at room temperature with a catalyst loading of 17.8 μgM/cm2.We found that the activity of NiFe2O4 improved over time-on-stream (+ 80 % in current at 1.65 V after 13.5 h) concurrent with a dissolution of Fe (2 – 8 wt% Fe loss). We hypothesize that the Fe content in NiFe2O4 (48 wt% Fe) was prohibitively high, and that dissolution of Fe shifted this value closer to optimum, resulting in higher activity. For NiFe (oxy)hydroxide materials, optimal Fe content has been reported at 15 - 25 wt% Fe.10 However, this value likely changes depending on the structure of the material and, relatedly, the relative abundances of Ni and Fe on the surface. We further looked at the effect of longer time on stream at 1.8 V (13.5 h – 27 h) and potentiodynamic cycling (1.4 - 1.8 V, 1.4 – 2.0 V, 0.0 – 2.0 V; 13.5 h) on NiFe2O4 stability. The results, in turn, showed that catalyst reactivity for OER improved over time-on-stream by 50 – 80% for potentiostatic holds and by upwards 500% for cycling tests (Fig. 1). This activity improvement was found to be concurrent with Fe dissolution (determined from ICP-MS), which ranged from 2 – 8 wt% Fe loss for the potentiostatic stress test to upwards of 40 wt% Fe loss for the cycling tests. Increased time on stream (13.5 – 27 h) was found to not significantly impact the activity enhancement. These results show a correlation between Fe dissolution and activity improvement and suggest that the activity of nanoparticle NiFe2O4 oxides may be electrochemical activated via this method, providing new insights into the viability of NiFe oxides as alternatives to IrO2 for OER.[1] Borup et al., Electrochem. Soc. Interface 2021, [2] IRENA Green Hydrogen Cost Reduction - Scaling up Electrolyzers to Meet the 1.5C Climate Goal 2020, [3] Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, 1974, [4] Suen et al., Chem. Soc. Rev. 2017, [5] Plevová et al., J. Power Sources 2021, [6] Burke et al., Chem. Mater. 2015, [7] Anderson et al., J. Electrochem. Soc. 2020, [8] McCrory et al., J. Am. Chem. Soc 2015, [9] European Commission, Report on Critical Raw Materials for the EU 2018, [10] Trotochaud et al., J. Am. Chem. Soc. 2014, [11] Anantharaj et al., Nano Energy 2021, [12] Li et al., Proc. Natl. Acad. Sci. 2017, [13] Görlin et al., J. Am. Chem. Soc. 2016, [14] Alia et al., J. Electrochem. Soc. 2019 Figure 1

Tuning assembly of Ni-doped Au@FexOy magnetoplasmonic nanowires for optimizing photochemical water splitting

The design of the particular geometric electrodes in photo-electrocatalysis is of significant importance to directly influence their catalytic performance. In this study, we have synthesized Ni-doped Au@FexOy magnetoplasmonic nanowires (MagPlas NWs) and leveraged diverse orientations of magnetic flux to disclose the active surfaces of the nanowire arrays incorporated into the electrode framework, thereby bringing to light active surface areas that facilitate adsorption of photons. Subjecting the Ni-Au@FexOy MagPlas NWs to magnetic fields at various orientations affects their light absorption intensity. The transverse mode exhibits impressive visible light absorption, which significantly increases its photocatalytic performance in oxygen evolution reaction (OER). The rugged forest shape array possesses remarkable visible light absorption, enhanced 2.01 mA cm−2 at 1.23 V vs. a reference hydrogen electrode (RHE), and long-term stability. The enhanced photoactivity is attributed to higher specific surface porosity and tuning of the magnetic field orientation to modulate the absorbance properties of the NWs.

Theory‐guided Design of Atomically Dispersed Dual‐Metal Catalysts for Superior Oxygen Reduction Reaction Activity

AbstractThe widespread application of electrochemical energy conversion devices, such as proton exchange membrane fuel cells, is hindered by the kinetically sluggish oxygen reduction reaction (ORR) at the cathode. Transition‐metal and nitrogen codoped carbon materials (TM−N−C) are among the most promising catalysts to solve this problem. Particularly, dual‐metal TM−N−C have already displayed excellent performance. However, further knowledge on the reaction mechanism and the structure−activity relationship is still required. In this study, we established three dual‐metal TM−N−C models (FeMn−N−C, FeCo−N−C, and FeNi−N−C) to investigate the electronic interaction between the metallic sites and their corresponding adsorption strength for oxygenated intermediates in ORR electrocatalysis. Then, using density functional theory calculations, we determined that the ORR activity of the dual‐metal TM−N−C models followed the order of FeCo−N−C > FeNi−N−C > FeMn−N−C. We confirmed the theoretically predicted activity by synthesizing atomically dispersed FeMn−N−C, FeCo−N−C, and FeNi−N−C catalysts using metal‐organic framework precursors, among which FeCo−N−C showed the best results in terms of ORR onset potential and half‐wave potential (0.92 and 0.81 V vs. the reference hydrogen electrode in 0.1 M HClO4, respectively.). The results demonstrate the feasibility of the theory‐guided rational design of efficient dual‐metal catalysts for ORR electrocatalysis.

Design and Characterization of a Close Compartment Hydrogen Reference Electrode for Electrocatalytic Studies

The reference electrode plays an important role in the determination of the electrocatalytic activity of a given electrode material. The hydrogen reference electrode has several advantages, as it is stable, can be used in the whole range of pH values, and does not contaminate the system. However, its use is not widespread due to certain difficulties related to its construction and operation. In this context, we report the design of a reversible hydrogen electrode (RHE) characterized by its simplicity, reproducibility, portability, stability, and precision. Moreover, rigorous equations for the variation of the RHE potential on the solution concentration, temperature, and pressure were derived as well as for the conversion of a working electrode potential referred to RHE to the standard hydrogen electrode (SHE).

Investigation of Ni- and Co-Based Bifunctional Electrocatalysts for Carbon-Free Air Electrodes Designed for Zinc-Air Batteries

Ni- and Co-oxide materials have promising electrocatalytic properties towards the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), and attract with low cost, availability, and environmental friendliness. The stability of these materials in alkaline media has made them the most studied candidates for practical applications such as a gas diffusion electrode (GDE) for rechargeable metal-air batteries. In this work, we propose a novel concept for a carbon-free gas GDE design. A mixture of catalyst (Co3O4, NiCo2O4) and polytetrafluoroethylene was hot pressed onto a stainless-steel mesh as the current collector. To enhance the electrical conductivity and, thus, increase ORR performances, up to 70 wt.% Ni powder was included. The GDEs produced in this way were examined in a half-cell configuration with a 6 M KOH electrolyte, stainless steel counter electrode, and hydrogen reference electrode at room temperature. Electrochemical tests were performed and coupled with microstructural observations to evaluate the properties of the present oxygen electrodes in terms of their bifunctionality and stability enhancement. The electrochemical behavior of the new types of gas-diffusion electrodes, Ni/Co3O4 and Ni/NiCo2O4, shows acceptable overpotentials for OER and ORR. Better mechanical and chemical stability of electrodes consisting of Ni/NiCo2O4 (70:30 wt.%) was registered. Doi: 10.28991/ESJ-2023-07-03-023 Full Text: PDF

Mixed Transition-Metal Oxides on Reduced Graphene Oxide as a Selective Catalyst for Alkaline Oxygen Reduction.

The development of highly efficient, stable, and selective non-precious-metal catalysts for the oxygen reduction reaction (ORR) in alkaline fuel cell applications is essential. A novel nanocomposite of zinc- and cerium-modified cobalt-manganese oxide on reduced graphene oxide mixed with Vulcan carbon (ZnCe-CMO/rGO-VC) was prepared. Physicochemical characterization reveals uniform distribution of nanoparticles strongly anchored on the carbon support resulting in a high specific surface area with abundant active sites. Electrochemical analyses demonstrate a high selectivity in the presence of ethanol compared to commercial Pt/C and excellent ORR activity and stability with a limiting current density of -3.07 mA cm-2, onset and half-wave potentials of 0.91 and 0.83 V vs reversible hydrogen reference electrode (RHE), respectively, a high electron transfer number, and an outstanding stability of 91%. Such a catalyst could be an efficient and cost-effective alternative to modern noble-metal ORR catalysts in alkaline media.

Nanotubular TiO x N y -Supported Ir Single Atoms and Clusters as Thin-Film Electrocatalysts for Oxygen Evolution in Acid Media.

A versatile approach to the production of cluster- and single atom-based thin-film electrode composites is presented. The developed TiO x N y -Ir catalyst was prepared from sputtered Ti-Ir alloy constituted of 0.8 ± 0.2 at % Ir in α-Ti solid solution. The Ti-Ir solid solution on the Ti metal foil substrate was anodically oxidized to form amorphous TiO2-Ir and later subjected to heat treatment in air and in ammonia to prepare the final catalyst. Detailed morphological, structural, compositional, and electrochemical characterization revealed a nanoporous film with Ir single atoms and clusters that are present throughout the entire film thickness and concentrated at the Ti/TiO x N y -Ir interface as a result of the anodic oxidation mechanism. The developed TiO x N y -Ir catalyst exhibits very high oxygen evolution reaction activity in 0.1 M HClO4, reaching 1460 A g-1 Ir at 1.6 V vs reference hydrogen electrode. The new preparation concept of single atom- and cluster-based thin-film catalysts has wide potential applications in electrocatalysis and beyond. In the present paper, a detailed description of the new and unique method and a high-performance thin film catalyst are provided along with directions for the future development of high-performance cluster and single-atom catalysts prepared from solid solutions.

Startup optimization of an automotive polymer electrolyte membrane fuel cell system with dynamic hydrogen reference electrodes

Efficient polymer electrolyte membrane fuel cell (PEM-FC) systems with minimal degradation are indispensable for automotive applications. A decisive measure to achieve this goal is the optimization of the startup procedure as part of the system operating strategy. This applies in particular to startups where the anode is partly or completely filled with ambient air after long downtimes. When displacing the air in the anode with hydrogen, damage to the cathode is inevitable and should be minimized. Basic approaches for this optimization are known from literature but are mainly derived from single cell and short stack experiments. In this paper, we optimize a full PEM-FC system by utilizing Dynamic Hydrogen Electrodes and show how gas replacement speed and half cell voltage evolution can be improved to mitigate degradation. The experimental results show that a homogeneous flow of the hydrogen/air front across the stack is to prioritize over its speed as only this enables additional upper voltage control in large stacks. The system optimum is achieved by maximizing startup pressure and purge valve flow, adapting the anode recirculation rate and precise voltage clipping. This study thus forms a procedural template for the optimization of the SUSD procedure in automotive fuel cell systems.

Surface Structure Engineering of PdAg Alloys with Boosted CO2 Electrochemical Reduction Performance

Converting carbon dioxide into high-value-added formic acid as a basic raw material for the chemical industry via an electrochemical process under ambient conditions not only alleviates greenhouse gas effects but also contributes to effective carbon cycles. Unfortunately, the most commonly used Pd-based catalysts can be easily poisoned by the in situ formed minor byproduct CO during the carbon dioxide reduction reaction (CRR) process. Herein, we report a facile method to synthesize highly uniformed PdAg alloys with tunable morphologies and electrocatalytic performance via a simple liquid synthesis approach. By tuning the molar ratio of the Ag+ and Pd2+ precursors, the morphologies, composition, and electrocatalytic activities of the obtained materials were well-regulated, which was characterized by TEM, XPS, XRD, as well as electrocatalytic measurements. The CRR results showed that the as-obtained Pd3Ag exhibited the highest performance among the five samples, with a faradic efficient (FE) of 96% for formic acid at -0.2 V (vs. reference hydrogen electrode (RHE)) and superior stability without current density decrease. The enhanced ability to adsorb and activate CO2 molecules, higher resistance to CO, and a faster electronic transfer speed resulting from the alloyed PdAg nanostructure worked together to make great contributions to the improvement of the CRR performance. These findings may provide a new feasible route toward the rational design and synthesis of alloy catalysts with high stability and selectivity for clean energy storage and conversion in the future.

Β-Feooh Nanorods As a Highly Active Self-Repairing Anode Catalyst for Alkaline Water Electrolysis Powered By Renewable Energy

The use of renewable energy as a primary energy source is urged because of the rapid progress of global warming. Because the renewable energy is unevenly distributed in terms of place and time, the production of hydrogen from renewable energy is crucial. Alkaline water electrolysis is a cost-effective technology for this purpose, though the degradation of electrodes under fluctuating power of renewable energy is recently regarded as a crucial problem. We have recently reported that a in-situ repair of anode catalyst (self-repairing catalyst), supplying fresh catalyst from electrolyte is quite useful to improve the lifetime under unsteady operation [1]. A hybrid cobalt hydroxide nanosheet (Co-ns) was used as the self-repairing catalyst, whereas its electrocatalytic activity is moderate. In this study, we demonstrate the use of β-FeOOH nanorods (β-FeOOH-nr) as a highly active and durable self-repairing catalyst. Because β-FeOOH-nr consists of iron as a metallic element, it is promising for its low cost and resource abundance. β-FeOOH-nr was synthesized by the coprecipitation of Fe3+ with tris(hydroxymethyl)aminomethane, followed by heating at 80 °C. The width and length of β-FeOOH-nr were 3–6 nm and 4–200 nm, respectively. The Fe K-edge XANES analysis showed that β-FeOOH-nr consists of Fe3+ species. Electrochemical tests were performed in a three-electrode PFA cell, using a nickel wire, a nickel coil, and a reversible hydrogen electrode, as working, counter, and reference electrodes, respectively. The β-FeOOH-nr was dispersed in 1 M KOH as an electrolyte. β-FeOOH-nr was first deposited on the nickel wire electrode by constant current electrolysis at 1 A·cm–2 for 240 min (30 min × 8 cycles). β-FeOOH-nr formed a thin layer of bundled nanorods and exhibited the oxygen evolution reaction (OER) overpotential of 320 mV at 100 mA cm–2, while previously reported Co-ns exhibited 342 mV. In addition, the activation of β-FeOOH-nr-coated electrode is almost finished at the first 30 min of the electrolysis, whereas Co-ns required 240 min for the activation. Because β-FeOOH-nr-coated electrode exhibited high OER activity with a small amount of β-FeOOH-nr deposited on the electrode, β-FeOOH-nr could activate electrode with shorted electrolysis time. The β-FeOOH-nr-coated electrode indicated the redox peak due to Ni2+/Ni3+ at 1.44 V vs. RHE which is at higher potential than that of a bare nickel electrode, implying that β-FeOOH-nr formed composite with active nickel species, such as Ni(OH)2 as highly active materials. The durability of the catalyst-coated electrode was examined in the presence of β-FeOOH-nr in the electrolyte by the newly reported shutdown-based accelerated durability test (SD-ADT) [2]. SD-ADT consists of multiple cycles of constant current electrolysis at 600 mA·cm–2 for 1 min and potential retainment at low potential of 0.5 V vs. RHE for 1 min. A bare nickel electrode is degraded only within 50 cycles by the SD-ADT (OER overpotential reached 640 mV at the 200th cycle), whereas β-FeOOH-nr-coated nickel electrode retained its low OER overpotential of 285 mV in at least 4000 cycles. Comparing with the SD-ADT in the absence of β-FeOOH-nr in the electrolyte, it was shown that β-FeOOH-nr was deposited during the SD-ADT to repair degraded electrode. In conclusion, β-FeOOH-nr was shown to be a useful anode catalyst for alkaline water electrolysis powered by fluctuating renewable energy. By dispersing β-FeOOH-nr in an electrolyte, the alkaline water electrolyzer can establish self-repairing system with very long lifetime under frequent potential change. The synchrotron radiation experiments were performed at the BL16B2 of SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2021A5310). This work was supported by the JSPS KAKENHI (grant number 20H02821) from Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. Part of this study uses outcomes of the development of fundamental technology for the advancement of water electrolysis hydrogen production in the advancement of hydrogen technologies and utilization projects (grant number JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

The Effects of Operating Conditions on the Electrode-Specific Potentials and Overall Performance of a Polymer Exchange Membrane Water Electrolyzer

Proton exchange member water electrolysis (PEMWE) is a crucial technology for the future of clean, sustainable energy systems. However, PEMWE cells use iridium metal as the anode catalyst, which is scarce and prone to high prices and price volatility. To address this problem, researchers have investigated different methods to increase catalyst utilization, thereby reducing catalyst loading and increasing overall MEA durability. One of the governing factors of the durability of both the cathode and anode catalyst is the redox state of the metal catalyst since Pt-dissolution occurs between ~0.9 and 1 V in the acidic conditions of the cell, and IrO2 reduces to Irmetal at potentials below ~1 V which is less stable than the oxide [1]. Past research has found that hydrogen crossover is one of the leading contributors to IrOx reduction since the overall cell potential goes to 0 V when held idle for a while [2]. This study used a custom-made hydrogen reference electrode to deconvolve the electrode-specific potentials under various operating conditions. It was found that anode catalyst loading, feedwater dissolved gas concentration, and cell voltage affect the electrode-specific potentials and the overall cell performance.[1] S. Song et al. 2008 Int J of Hydrogen Energy 2008;33:4955–61[2] P. J. Rheinländer and J. Durst 2021 J. Electrochem. Soc. 168 024511

Cobalt-based co-ordination complex-derived nanostructure for efficient oxygen evolution reaction in acidic and alkaline medium

Electrochemical water splitting is one of the most important method for energy conversion and storage. For this, the design and development of a low-cost robust electrocatalyst are highly desirable. In this study, Cobalt-based electrocatalyst for Oxygen Evolution Reaction was synthesized by thermal treatment of Cobalt-dehydroacetic acid (Co-DHA). The as-synthesized Co nanostructures and Co-DHA crystals were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy thermo-gravimetric analysis, and field emission scanning electron microscopy. The electrochemical O2 evolution study shows the overpotential (at 10 mV/cm−2) correspond to 294 mV vs reference hydrogen electrode (RHE) for K-300 (Co3O4@300), whereas K-500 (Co3O4@500) shows 170 mV vs RHE values in 1 M KOH solution, respectively. Similar trends have been observed for electrochemical O2 evolution studies in 0.5 M H2SO4, where K-300 and K-500 shows the overpotential (at 10mV/cm−2) of 234 mV vs RHE, and 199 mV vs RHE, respectively. The outcomes show better catalytic efficiency of K-500 as compared to K-300.

Cobalt Quaterpyridine Complexes for Highly Efficient Heterogeneous CO2 Reduction in Aqueous Media

AbstractLigands play a critical role in the electrocatalytic CO2 reduction reaction (CO2RR) based on heterogeneous molecular catalysts. Previous research on heterogeneous molecular electrocatalysis has mainly dealt with N4 ligands with pyrrole as subunits (porphyrin, phthalocyanine, etc.), while ligands constructed from pyridine subunits remain uncommon. The examples for comparing active configurations are few and far between. Herein, the development of new N4 cobalt complexes based on pyridine subunits is explored. After anchoring onto carbon nanotubes, they can exhibit CO2RR activity at a low overpotential of 140 mV, and high activity from ‐0.30 to ‐0.60 V versus reference hydrogen electrode with a selectivity of above 98%. Excellent performance at large current densities can also be observed in a flow cell. In situ attenuated total reflectance‐Fourier transform infrared spectroscopy proves that such electrocatalysts exhibit CO production at lower overpotential and moderate CO adsorption ability over a wide potential range. From density functional theory calculations, it is shown that a pyridine‐based cobalt complex on a carbon substrate can reduce the Gibbs free energy for reactions further than its counterpart pyrrole‐based ones. Further analysis proves that the semimetal behavior of optimized d‐orbitals may facilitate charge transfer and increase the activity. This provides a new insight for understanding catalytically active moieties in heterogeneous molecular catalysts with ligands constructed from pyridine subunits.

High-performance bulk heterojunction-based photocathode with facile architecture for photoelectrochemical water splitting

Organic semiconductors are promising candidates as photoactive layers for photoelectrodes used in photoelectrochemical (PEC) cells due to their excellent light absorption and efficient charge transport properties with the help of interfacial materials. However, the use of multilayers will make the charge transfer mechanism more complicated and decrease the PEC performance of the photoelectrode caused by the increased contact resistance. In this work, a PM6:Y6 bulk heterojunction (BHJ)-based photocathode is fabricated for efficient PEC hydrogen evolution reaction (HER) in an acidic aqueous solution. With RuO2 as an interfacial modification layer, the photocathode with a simple structure (fluorine-doped tin oxide (FTO)/PM6:Y6/RuO2) generates a maximum photocurrent density up to −15 mA/cm2 at 0 V vs. reference hydrogen electrode (RHE), outperforming all previously reported BHJ-based photocathodes in terms of PEC performance. The highest ratiometric power-saved efficiency of 3.7% is achieved at 0.4 V vs. RHE.