Re-adsorption of leached Cr species during the surface reconstruction of NiFeCr layered double hydroxides enhances the oxygen evolution reaction

Abstract

Cr leaching is anticipated to extensively advance the activity of Cr-containing catalysts towards the oxygen evolution reaction (OER), but the underlying catalytic enhancement mechanism requires further investigation. Herein, NiFeCr layered double hydroxide (NiFeCr-LDH) is proposed as a proof-of-concept catalyst to elucidate the evolution of Cr species and its enhancement mechanism in OER. The incorporation of Cr(Ⅲ) ions into the lattice of NiFe-LDH is achieved through a meticulously controlled electrodeposition process, which not only promotes Cr leaching but also deepens surface reconstruction. More importantly, experimental and theoretical results demonstrate that protogenetic CrO₄²⁻ anions, derived from the oxidation of leached Cr ions, adsorb onto the surface NiFeCr-LDH under the anodic potential to create a CrO₄²⁻-rich electrical double layer (CrO₄²⁻-rich EDL) and function as co-catalyst to trigger OER. CrO₄²⁻-rich EDL integrated with vacancies balances the Gibbs free energies of the reconstructed NiFeCr-LDH for oxygen-containing intermediates, resulting in an exceptionally low overpotential of 286 mV at 500 mA cm⁻², which outperforms most state-of-the-art metallic catalysts. Additionally, the anion exchange membrane water electrolysis system assembled with NiFeCr-LDH and Pt/C demonstrates 1000-h stability at a current density of 1.0 A cm⁻² under a voltage of 1.74 V (at 70 °C), highlighting its promising potential for practical, large-scale and sustainable applications.