Al2O3-assisted hierarchical Ni–Al surface alloying for scalable fabrication of nano-roughened Ni foam cathodes with superior HER activity and durability in alkaline water electrolysis

Abstract

Plate-type electrodes in zero-gap alkaline water electrolysers often suffer from severe gas-bubble accumulation and sluggish mass transport, which diminish the effective electrochemically active surface area (ECSA) and retard hydrogen evolution reaction (HER) kinetics. Herein, we report an Al₂O₃-assisted surface-modification strategy that converts Ni foam into a hierarchically structured, catalyst-free HER cathode with markedly enhanced activity and durability in concentrated alkaline media. During thermal alloying, Al₂O₃ nanoparticles act as morphological regulators that promote the formation of finely dispersed Ni–Al phases while suppressing Ni coarsening, thereby stabilizing the evolving surface structure. Subsequent alkaline leaching generates a dual-scale porous architecture comprising microscale pores and secondary nanoscale roughness. The resulting electrode (m-NF_A) exhibits a tenfold increase in double-layer capacitance (C_dl = 104.2 mF cm⁻²) relative to pristine Ni foam, indicating a substantially enlarged accessible surface area. In 30 wt% KOH half-cell tests, m-NF_A delivers an overpotential of 157.8 mV at 100 mA cm⁻² and a Tafel slope of 69 mV dec⁻¹, signifying facilitated water dissociation kinetics. Notably, the hierarchical surface shows superhydrophilicity with a near-zero water contact angle, which alleviates bubble pinning and promotes rapid gas detachment under high-rate operation. When implemented as the cathode in a zero-gap alkaline water electrolysis single cell (80 °C, Zirfon PERL 220), m-NF_A demonstrates stable load-following behaviour and durability over 1000 load cycles (200–1000 A cm⁻², 66 h), reaching cell voltages of 1.72 and 2.00 V at 200 and 1000 mA cm⁻² at 1000 cycles. Collectively, this Al₂O₃-mediated modification strategy provides a scalable and cost-effective pathway to high-performance, non-noble metal HER electrodes for renewable-energy-driven alkaline electrolysis.