Insight into the oxygen evolution reaction mechanism catalyzed by phosphate-substituted FeCo2O4 nanosheets: proton-coupled electron transfer assisted adsorbate evolution mechanism investigated by in situ NAP-XPS

Abstract

This study investigates phosphate-substituted FeCo₂O₄ nanosheets for the oxygen evolution reaction (OER), emphasizing their enhanced electrochemical performance. The substitution of phosphate anions disrupts the catalyst's lattice structure, introducing additional defects while enabling an alternative oxidation pathway. This modification significantly enhances the catalytic performance, yielding a lower overpotential, reduced charge transfer resistance, increased electrochemically active surface area, higher double-layer capacitance, and faster catalytic kinetics compared to pristine FeCo₂O₄. In situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) reveals the formation of Co(IV), a key indicator of catalytic efficiency, and identifies H-phosphate as an intermediate facilitating proton transfer from Co(OH)₂ and CoOOH to phosphate during the reaction. Complementary density functional theory calculations demonstrate that phosphate functionalization stabilizes critical intermediates (–OH* and –OOH*) at Fe and Co active sites, reducing activation energy barriers. These findings align with experimental results and support a proton-coupled electron transfer assisted adsorbate evolution mechanism for OER on phosphate-substituted FeCo₂O₄ nanosheets.