Impact of Phosphide–Phosphate Ratio on NiCoP Catalysts for Hydrogen Evolution in Anion Exchange Membrane Water Electrolysis

Abstract

Alkaline and anion exchange membrane water electrolysis (AEMWE) presents a promising approach for hydrogen production. However, the slow kinetics of the alkaline hydrogen evolution reaction (HER) remains a significant challenge. This study aimed to enhance HER activity by optimizing transition metal-phosphorus compound catalysts, including Ni, Co, NiCo, NiP, CoP, and NiCoP. Their surface structure, crystallinity, electrochemical properties, and HER performance were meticulously studied. Among the catalysts, Ni₂₈Co₆₂P₁₀ exhibited exceptional HER performance, achieving a low overpotential of 48 mV at a current density of −10 mA cm^–2 in 1 M KOH. X-ray photoelectron spectroscopy analysis revealed that an optimal 1:1 balance of phosphate to phosphide is critical for achieving efficient HER. These findings emphasize the importance of balancing phosphorus species for optimal alkaline HER catalysis. Moreover, Ni₂₈Co₆₂P₁₀ demonstrated excellent durability, maintaining high performance after 5000 cycles. In AEMWE single-cell tests, the catalyst achieved a cell voltage of 1.88 V at 1 A cm^–2, surpassing the performance of Ni/Co-based catalysts from previous studies. The NiCoP-based catalysts in this study presented considerable promise for AEMWE systems, paving the way to the development of more efficient and durable catalysts for hydrogen production and advancing hydrogen-based renewable energy technologies.