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Summary: Developing a non‐precious or low Pt‐group metal‐containing (low‐PGM) hydrogen oxidation reaction (HOR) catalyst is crucial to fabricate economic anion exchange membrane fuel cells (AEMFCs), an alternative to proton exchange membrane fuel cells (PEMFC). In this study, low‐PGM Ni100‐xRhx electrocatalysts, seldomly studied as alkaline HOR catalysts, with various compositions are fabricated via electrodeposition. Substantial changes are observed in both the morphology and crystalline structure of the catalysts when Ni is alloyed with Rh, such as enlarged surface area and development of different textures. The HOR activities of Ni100‐xRhx catalysts evaluated in 0.1 M KOH solution are dramatically enhanced because of the enlarged surface area, bifunctional roles of H‐providing sites (Ni/Rh) and OH‐providing sites (Ni[OH]2/Rh2O3), and their balanced composition on the surface. The durability of Ni89Rh11, the most appropriate catalyst, is investigated with the 3000 potential cycling, giving the average decay rate of approximately 0.30 μA cm−2/cycle. The origin of enhanced activity and degradation during durability test was explained in terms of the electronic structures and surface composition of the catalysts. The initial high HOR activity of about 1.5 mA/cm2 for Ni89Rh11 at 0.05 VRHE, though it requires a further improvement in the durability, suggests the practical feasibility of it as a low PGM alkaline HOR catalyst. [ABSTRACT FROM AUTHOR]

Summary: To realize nonprecious‐metal catalysts with practical applicability for the hydrogen evolution reaction (HER), improved corrosion resistance and catalytic activity are required. In this study, composition‐controlled Co‐Cu alloys were fabricated by electrodeposition for use as HER catalysts in proton exchange membrane water electrolyzers (PEMWEs). As the Cu content in the alloy increased, the morphology changed from needle‐shaped particles to small round particles. Furthermore, a phase transition from a hexagonal close‐packed structure to a face‐centered cubic structure occurs because the latter structure is stabilized by adding Cu to Co. The optimum catalyst composition for the HER was found to be Co59Cu41, which had an overpotential of 342 mV at −10 mA cm−2. This catalyst exhibited excellent durability, showing a potential reduction of approximately 100 mV over 12 hours under a constant current density. This superior performance was attributed to the increase in the electrochemical surface area resulting from the addition of Cu, as confirmed by electrochemical double layer capacitance measurements, in addition to a counterbalance between the hydrogen adsorption energies of Co and Cu. Finally, the application of the Co‐Cu alloy catalyst as a cathode catalyst in a PEMWE resulted in excellent performance of 1.2 A cm−2 at 2.0 Vcell. [ABSTRACT FROM AUTHOR]

In this work, the catalytic activities of electrodeposited Ag and AgIn bimetallic dendrites have been explored for electrochemical reduction of CO 2 to CO. In the case of Ag dendrites, the Ag crystal structure was found to be affected by the deposition potential and showed different Ag(220)/Ag(111) ratios. The Faradaic efficiencies to produce CO increased as this ratio increased, whereas the partial current densities for CO generation were found to have a stronger relationship with the roughness of the Ag catalyst. The electrodeposition of AgIn was carried out to investigate the effect of addition of In and its content on the catalytic performance, while maintaining the dendritic morphology. The crystal structures of AgIn dendrites were found to vary with the amount of added In, demonstrating a linear increase in the ratio Ag(220)/Ag(111) with increasing In content and a positive impact on the production of CO. Furthermore, there was a competition between the suppression of the hydrogen evolution reaction (HER) vs. the decrement in the amount of active Ag with increasing addition of In. It was found that these complementary effects resulted in a superior CO Faradaic efficiency of AgIn dendrites with a volcano shaped curve based on the In content. The complementary effect on the catalytic activity could be extended to the various reduction potentials, indicating the significant effect of HER suppression at highly negative reduction potentials. [ABSTRACT FROM AUTHOR]

For the improvement for the commercialization of electrochemical carbon dioxide (CO2) conversion technology, it is important to develop a large area Ag gas diffusion electrode (GDE), that exhibits a high electrochemical CO2 conversion efficiency and high cell performance in a membrane electrode assembly (MEA)-type CO2 electrolyzer. In this study, the electrodeposition of Ag on a carbon-paper gas diffusion layer was performed to fabricate a large area (25.5 and 136 cm2) Ag GDE for application to an MEA-type CO2 electrolyzer. To achieve uniformity throughout this large area, an optimization of the electrodeposition variables, such as the electrodes system, electrodes arrangement, deposition current and deposition time was performed with respect to the total electrolysis current, CO production current, Faradaic efficiency (FE), and deposition morphology. The optimal conditions, that is, galvanostatic deposition at 0.83 mA/cm2 for 50 min in a horizontal, two-electrode system with a working-counter electrode distance of 4 cm, did ensure a uniform performance throughout the electrode. The position-averaged CO current densities of 2.72 and 2.76 mA/cm2 and FEs of 83.78% (with a variation of 3.25%) and 82.78% (with a variation of 8.68%) were obtained for 25.5 and 136 cm2 Ag GDEs, respectively. The fabricated 136 cm2 Ag GDE was further used in MEA-type CO2 electrolyzers having an active geometric area of 107.44 cm2, giving potential-dependent CO conversion efficiencies of 41.99%–57.75% at Vcell = 2.2–2.6 V. [ABSTRACT FROM AUTHOR]

Electrodeposited Cu x Mo 100 − x catalysts were prepared on a Ti substrate for the hydrogen evolution reaction (HER) in acidic medium. By varying the electrolyte composition for electrodeposition, the atomic concentration of the Cu x Mo 100 − x electrocatalysts could be controlled, and the Mo content ranged between 0.8 and 6.9%. In the first cyclic voltammetry scan in a 0.5 M H 2 SO 4 electrolyte, the recorded HER current densities of the Cu x Mo 100 − x electrocatalysts at −0.50 V RHE increased on increasing the Mo content to 3.8%; then, a further increase in Mo to 6.9% led to a saturation in the HER activity. The maximum value of the normalized current density with respect to the electrochemical surface area and the loading mass was found for the Cu 99.2 Mo 0.8 electrocatalyst. Characterization of the prepared catalysts revealed that the enhancement of catalytic activity originates from changes in the grain size and electronic structure. To operate a single cell of the proton exchange membrane water electrolyzer (PEMWE), we electrodeposited CuMo catalyst on carbon paper, and this was used as the cathode, while IrO 2 electrodeposited on carbon paper was used as the anode. The cell performance was normalized with respect to the metal mass loading and was found to be 3.4 A/mg metal at 1.9 V, a 2.2–10.8 times better catalyst cost-activity relationship compared to that of currently reported PEMWEs using Pt-based cathodes. Consequently, the results presented here show that non-noble metal cathodes can be used for PEMWE operation. [ABSTRACT FROM AUTHOR]