Electrolyte-Modulated Electrodeposition of Bimetallic Alkaline Hydrogen Evolution Catalysts for Anion Exchange Membrane Water Electrolyzers

We report the fabrication of a cobalt–molybdenum (Co–Mo) heterohierarchical thin-film catalyst electrodeposited on nickel foam (NF) via a facile one-step electrodeposition method for efficient hydrogen evolution reaction (HER) under alkaline conditions. A comprehensive study of alkali and alkaline earth metal halide coelectrolytes demonstrated that the coelectrolyte used during electrodeposition directly governs the Co–Mo catalyst morphology and the degree of Mo incorporation. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and inductively coupled plasma–atomic emission spectroscopy analyses showed that using calcium chloride (CaCl2) as the coelectrolyte considerably improved uniform Mo incorporation and facilitated cobalt hydroxide deposition. The optimized Co–Mo/NF–CaCl2 catalyst showed an overpotential of 100 ± 6 mV at −10 mA/cm2, along with improved charge transfer and active site density, attributed to the better double-layer capacitance and tailored surface microstructure. This study is the first to correlate the coelectrolyte identity in electrodeposited Co–Mo catalysts with HER performance and contributes insights into the bimetallic electrodeposition technique. The high performance and alkaline compatibility of the catalyst make it a promising candidate for sustainable hydrogen generation via anion exchange membrane water electrolysis.