Sputtered Ni and Ni₄Mo Catalysts at Low Loadings for the Alkaline Hydrogen Evolution Reaction in AEM Water Electrolyzers

Reducing catalyst material usage while maintaining high performance is critical for scalable green hydrogen production via electrolysis. In this work, low-loading alkaline hydrogen-evolution reaction (HER) cathodes are fabricated by direct current magnetron sputtering of Ni and Ni₄Mo, providing a one-step, solvent-free route to catalyst-coated substrates. By tuning sputter power and Ar pressure, the deposited layers are steered toward rough nanostructures with increased accessible surface area, which correlates with improved HER activity compared with denser reference films, as shown by three-electrode measurements. The sputtered Ni-Mo has the targeted Ni₄Mo composition and exhibits a nanocrystalline Ni-fcc-type structure rather than the equilibrium intermetallic phase. Process transfer from planar substrates to porous carbon paper yields catalyst loadings of 0.046-0.186 mg cm⁻² (Ni) and 0.053-0.318 mg cm⁻² (Ni4Mo). Three-electrode electrochemical benchmarking showed decreasing HER overpotential with increasing loading, reaching ~104 mV at 10 mA cm⁻² for a NiMo cathode with 0.21 mg/cm². Implemented in a PGM-free AEM electrolyzer, along with an uncatalyzed stainless steel anode, Ni4Mo outperforms Ni at high current densities, delivering 1.95 V at 1 A cm⁻² and 60 °C (1.88 V at 80 °C) and enabling a mass activity of ~4.7 A mg⁻¹ at 1.95 V. A 500 h steady-state durability experiment at 1 A cm⁻² demonstrates stable performance with a reduced degradation rate toward the end of the test.