Using PTL Architecture and Surface Chemistry to Control the Nucleation, Distribution, and Morphology of Self-Supported PGM-Free AEM Cathodes

Abstract

Self-supported electrodes are increasingly being used in anion exchange membrane electrolyzers. However, a clear understanding of the effects of substrate chemistry and structure is lacking. NiMoO4 nanorods were hydrothermally grown from sodium molybdate and ammonium heptamolybdate precursors onto a series of porous electrode supports, including Ni foams and felts, and sintered metal-fiber-derived porous transport layers made of Ni, stainless steel, and Hastelloy-X. The Mo precursor primarily influenced the growth mechanism, while substrate architecture controlled morphology and anchoring behavior. When implemented as cathodes in an anion exchange membrane water electrolyzer, the electrodes exhibited substrate-dependent activation behavior at the beginning of life, which was linked to the spatial accessibility of the nanorods. However, their electrochemical performance converged during steady-state operation after more than 70 h, regardless of precursor or substrate. These results establish a mechanistic basis connecting precursor chemistry, substrate selection, and structural development, enabling rational integration of NiMo4-based self-supported electrodes into fully PGM-free alkaline electrolyzer platforms.