Synergistic Lattice-Strain and Electronic Modulation in Cobalt Oxide for Enhanced Proton Exchange Membrane Water Electrolysis

Spinel cobalt oxide (Co₃O₄) is a promising alternative to IrO₂ for acidic oxygen evolution reaction (OER) electrocatalysts, but its application is hindered by high overpotentials and poor stability. Here, an F-In-Co₃O₄ catalyst was developed via co-doping indium (In) and fluorine (F), which introduces lattice strain and elongates the octahedral [CoO₆] structure. X-ray absorption spectroscopy (XAS) and theoretical calculations indicate that the bonding strength between Co_Oh³⁺ and the top and side oxygen atoms is a key factor influencing both OER catalytic activity and stability. This lattice strain alters the Co-O bonding configuration at side-oxygen sites and is associated with improved structural integrity, while simultaneously facilitating the desorption of OER intermediates during the OER process, thereby reducing the overpotential. Additionally, ab initio molecular dynamics (AIMD) simulations and ex situ X-ray photoelectron spectroscopy (XPS) analysis show that In³⁺ acts as an electron donor, effectively suppressing cobalt overoxidation and subsequent ion dissolution. Consequently, F-In-Co₃O₄ achieves an overpotential of 462 mV at 100 mA cm^-2 in 0.5 M H₂SO₄, outperforming commercial IrO₂. Moreover, a proton exchange membrane (PEM) electrolyzer employing F-In-Co₃O₄ maintains stable operation for over 100 h, underscoring its promise for practical water-splitting applications.