Synthesis, Optimisation, and Characterisation of Non-Noble Low-Cost Ni-Mo Electrocatalysts for Green Hydrogen Production via Anion Exchange Membrane Water Electrolysis

Abstract

Anion exchange membrane water electrolysis (AEMWE) encounters challenges related to stability and catalytic efficiency. This research investigates the use of Ni-Mo catalysts for the hydrogen evolution reaction (HER) within AEMWE, with a focus on optimising preparation conditions, including pH, applied potential, and plating methods on a carbon cloth substrate. An investigation employing electrochemical quartz crystal microbalance with energy dispersive spectroscopy reveals that a more alkaline environment (pH≈10), combined with a more negative applied potential (≤ −1.8 VSCE), results in increased Ni-Mo deposition. Consequently, increased the Mo mass fraction in NiMo alloy reported to be better for catalysis. HER electrocatalytic activity assessment, conducted via a rotating disk electrode, demonstrates a notable enhancement in catalytic performance within the pH range of 9 to 10, reaffirming the pH-dependent nature of catalysis. However, catalytic efficacy diminishes beyond pH 10. Notably, an overpotential analysis pinpoints the catalyst prepared at pH 10, with an applied potential of −2.2 VSCE, as exhibiting superior performance in the HER (with an overpotential of 88.9 mV at 10 mA/cm2 ). Diverse plating techniques were employed to regulate morphology, with the custom-built reactor displaying exceptional performance and yielding a smooth surface structures with a remarkable Mo to Ni mass ratio of approximately 0.22. The proposed Ni-Mo catalyst delivers a current density of 1.6 A/cm2 at a 1.8 cell potential, surpassing pure Ni by 76%, and demonstrating comparable performance to commercial Pt in an AEMWE setup, operating under conditions of 1M KOH and 60 ◦C. This achievement was obtained with a pH of 10, utilising 0.2 M nickel(II) sulfate, 0.12 M sodium molybdate, 0.7 M ammonia, and 0.25 M sodium citrate, plated on carbon cloth using a custom-built reactor with pulse plating at −2.2 VSCE applied potential for 15 min. Collectively, this study underscore the potential of Ni-Mo as a cost-effective alternative to Pt in AEMWEn for H2 evolution, bolstering the quest for affordable and environmentally friendly hydrogen fuel production. Keywords: anion exchange membrane, water electrolyser, green hydrogen, HER, electrocatalyst preparation, Ni-Mo.