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 electrolyzers suffer from severe gas-bubble accumulation and sluggish mass transport, which limit the effective electrochemically active surface area (ECSA) and HER kinetics. Herein, we report an Al₂O₃-assisted surface-modification strategy for Ni foam that transforms it into a hierarchically structured, catalyst-free HER cathode with markedly enhanced activity and durability under alkaline conditions. Ni foam was coated with an Al-Al₂O₃-PEG slurry and subjected to heat treatment followed by alkaline chemical leaching, yielding a porous Ni framework decorated with secondary nanoscale roughness. Structural and chemical characterization (SEM, XRD, XPS, EDS) revealed that Al₂O₃ nanoparticles promote the formation and dispersion of Ni-Al intermetallic and NiAl₂O₄ nanoflake phases, which are selectively removed during leaching to generate a nano-textured surface. This architecture increases the ECSA by an order of magnitude relative to pristine Ni foam and stabilizes the nanoscale morphology. In half-cell HER tests, the optimized m-NF_A electrode achieves an overpotential of 157.8 mV at 100 mA cm^-2 (≅ 66% lower than pristine Ni foam) and a reduced Tafel slope of 69 mV dec_-1, with EIS confirming significantly lower porous-structure and charge-transfer resistances. ECSA-normalized analysis shows that the hierarchical nano-roughness enhances intrinsic catalytic activity while mitigating bubble-induced active-site blocking. When implemented as a cathode in an alkaline water electrolysis single cell, m-NF_A delivers lower cell voltages, superior load-following behavior, and stable operation under stringent durability tests, including half-cell AST (-10 and -400 mA cm^-2, 12 h) and full-cell load cycling (0.2-1.0 A cm^-2, 1000 cycles). These findings establish Al₂O₃-mediated hierarchical surface modification of Ni foam as a scalable and effective design principle for high-performance, noble-metal-free HER electrodes compatible with renewable-energy-driven alkaline electrolysis.