Molten-salt flash synthesis of P-doped iron oxide with engineered oxygen vacancies for lattice-oxygen water oxidation

Abstract

Industrial anion exchange membrane water electrolysis (AEMWE) still lacks earth-abundant oxygen evolution reaction (OER) catalysts that simultaneously exhibit high intrinsic activity and long-term durability. This limitation mainly originates from the conventional adsorbate evolution mechanism (AEM), which is restricted by the linear scaling relationship between *OOH and *O intermediates. Herein, we propose a rapid diffusion strategy based on molten-salt-assisted approach to synthesize P/FeO_x. The entire synthesis completes within minutes via high-temperature solid-state interdiffusion, enabling single-batch production at the kilogram scale with exceptional time and energy efficiency. Phosphorus doping successfully narrows the band gap between Fe 3d and O 2p, thus enhancing electronic conductivity. It also promotes the formation of O_v and induces a mechanistic transition from the AEM to the lattice-oxygen oxidation mechanism (LOM) pathway, simultaneously reducing the activation barrier for the *OH → *O step. The optimized catalyst achieves an overpotential of 256 mV at 100 mA cm⁻² and maintains stable operation for over 2000 h at 100 mA cm⁻² without noticeable degradation. When integrated into an AEMWE device, the membrane-electrode assembly requires merely 1.78 V to deliver 500 mA cm⁻² and operates stably for 1000 h. In conclusion, this study presents a rational synthesis approach and practical design principles for engineering high-performance OER electrocatalysts tailored to industrial water electrolysis.