Low-cost, high-performance electrodes for PGM-free AEM water electrolyzers: Structural optimization of NiMo-based cathodes

Water electrolysis technologies for hydrogen production are receiving significant attention due to a drastic reduction in the cost of renewable energy sources in recent years. Though traditional alkaline and proton exchange membrane water electrolyzers are receiving the most commercial attention, the anion exchange membrane water electrolyzer (AEMEL) has the potential to be much lower in cost. AEMELs have recently shown remarkable progress in terms of performance and durability. However, they are still mostly operated with expensive platinum group metal (PGM) catalysts on both the anode and cathode. To achieve low cost, either PGM-free or ultra-low loading PGM catalysts are needed. In this study, several NiMo-based catalysts are evaluated as PGM-free electrocatalysts for the hydrogen evolution reaction (HER), with a focus on understanding how the catalyst structure impacts not only intrinsic activity but also the resulting electrode structure and performance. It is shown that the operating voltage of an AEMEL can be reduced by 120 mV at 1.0 A/cm² at 60 °C in 0.3 M KOH just by changing the physical properties of the catalyst. The resulting best-performing NiMo-based is then paired with Lanthanum Strontium Cobalt (LSC) to create completely PGM-free AEMELs with strong performance, though still lower than PGM-containing cells. This study demonstrates that both the physical properties of the catalyst powder and the electrode layer significantly impact cell performance, provides important insights for development of AEM-based water electrolyzer systems, and takes an active step towards AEMEL commercial viability. • High performance AEM water electrolyzer using PGM-free electrocatalysts • Optimization of HER electrode performance achieved through modification of catalyst structure • Cathode catalyst physical properties affected cell operation by 120 mV at 1.0 A/cm² • Design principles for PGM-free cathodes are proposed