Improving activity and stability assisted by the self-conversion of carbon oxyanions for large-current-density water electrolysis

Abstract

Developing efficient and stable oxygen evolution reaction (OER) catalysts for anion exchange membrane water electrolysis (AEMWE) under industrial current densities remains a significant challenge. Herein, we report a self-optimizing NiFeOOH catalyst via in situ reconstruction of nickel‑iron oxalate ((NiFe)C₂O₄) coupled with dynamic carbon oxyanion conversion. Operando electrochemical impedance spectroscopy and Raman spectroscopy reveal that oxalate ligands accelerate charge transfer and promote the deep oxidation of Ni to active Ni⁴⁺ species. Combined with theoretical calculations, it is found that spontaneously adsorbed carbonate ligands induce dual electronic modulation: (1) Stabilizing Ni⁴⁺ through metal-to-ligand charge transfer and enhancing OH^- adsorption kinetics; (2) Lowering the Fe 3d band center and strengthening FeO covalency, which weakens *OH adsorption and inhibits Fe dissolution. The optimized catalyst achieves extremely low overpotentials: 227 mV at 100 mA cm^-2 and 300 mV at 1 A cm^-2, and exhibits^-2, with a sixfold stability improvement at 1 A cm^-2 compared to conventional NiFe hydroxides. In practical AEMWE single cells, it delivers 0.5 A cm^-2 at 1.65 V and 1.0 A cm^-2 at 1.76 V, while maintaining stable performance for 500 h at 0.2 A cm^-2. This dynamic ligand-catalyst interplay strategy breaks the activity-stability trade-off, advancing industrial water electrolysis.

Keywords: Anion exchange membrane water electrolysis; Carbon oxyanion; Metal dissolution; Oxygen evolution reaction; Stability.