In Situ Phase Transformation-Induced High-Activity Nickel–Molybdenum Catalyst for Enhancing High-Current-Density Water/Seawater Splitting

Abstract

Anion exchange membrane water electrolyzer (AEMWE) represents a promising sustainable method for large-scale industrial-grade hydrogen manufacturing. However, the sluggish kinetics of the bifunctional oxygen/hydrogen evolution reaction (OER/HER) electrocatalysts makes it imperative to develop high-performance anode and cathode materials. Herein, P-doped β-phase NiMoO₄ (p-β-NiMoO₄) nanorods were first constructed as the cathode material for HER, and then α-phase NiMoO₄ (p-β-NiMoO₄-A) derived by an electrochemical phase transformation mechanism was further applied for OER. A series of characterizations supported that applying sufficient anode potential to β-NiMoO₄ can drive the phase transformation from beta to alpha. Compared with the directly prepared counterpart, this dynamic phase transformation results in the catalyst tuning the atomic configuration environment, modifying the electronic state, and optimizing the *OH adsorption ability. Consequently, the assembled two-electrode electrolytic cell system contributes remarkable overall water/seawater splitting capacity and outstanding long-term durability even under industrial-grade operating conditions. The AEMWE device with an ultralow cell voltage of 2.15 V at 2.0 A·cm^–2 current density confirms the applicability of anode and cathode electrocatalysts. This study could provide a promising path to realize the efficient phase transition of nickel–molybdenum-based materials for industrial clean energy conversion.