Hierarchical NiFeMoO₄ Precatalyst Reconstructed NiFeOOH Anodes for Efficient and Durable Anion-Exchange Membrane Water Electrolysis

Anion-exchange membrane water electrolysis (AEM-WE) offers a promising alternative for efficient water electrolysis, providing low-cost and high-purity hydrogen production. However, the slow reaction kinetics associated with the oxygen evolution reaction (OER) continue to pose a significant obstacle. In this work, we synthesized nanometer micron hierarchical NiFeMoO_<i>x</i> as OER precatalysts, which were completely reconstructed into hierarchical NiFeOOH (<i>h-</i>NiFeOOH), demonstrating remarkable OER activity, with overpotentials of 162/245 mV required to achieve current densities of 10/1000 mA cm^-2 in 1.0 M KOH. Additionally, it demonstrated robust stability exceeding 1000 h at 1000 mA cm^-2. Furthermore, <i>h-</i>NiFeOOH demonstrated excellent long-term stability in AEM-WE, maintaining a current density of 1000 mA cm^-2 at a cell voltage of 1.55 V (80 °C) for over 160 h and achieving a reliable performance beyond 1000 h at room temperature. <i>In situ</i> analyses, including X-ray absorption fine structure (XAFS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), combined with density functional theory (DFT) calculations, reveal that the OER process of <i>h-</i>NiFeOOH primarily follows an adsorption evolution mechanism (AEM) at the Ni site. Meanwhile, Fe³⁺ acts as a Lewis acid, promoting Ni valence and thereby enhancing the OER performance. This study emphasized the crucial role of precatalyst engineering for efficient NiFe-based catalysts and analyzed the role of Fe in the OER catalytic cycle.