Tailoring Octahedron-Tetrahedron Synergism in Spinel Catalysts for Acidic Water Electrolysis

The instability issues of oxide-based electrocatalysts during the oxygen evolution reaction (OER) under acidic conditions, caused by the oxidation and dissolution of the catalysts along with the current-capacitance effect, constrain their application in proton exchange membrane water electrolysis (PEMWE). To address these challenges, we tailored the spinel structure of Co₃O₄ and exploited the synergism between the tetrahedron and octahedron sites by partially substituting Co with Ni and Ru (denoted as NiRuCoO_<i>x</i>), respectively. Such a catalyst design creates a Ru-O-Ni electronic coupling effect, facilitating a direct dioxygen radical-coupled OER pathway. Density-functional theory (DFT) calculations and <i>in situ</i> Raman spectroscopy results confirm that Ru is the active site in the diatomic oxygen mechanism while Ni stabilizes lattice oxygen and the Ru-O bonding. The designed NiRuCoO_<i>x</i> catalyst exhibits an exceptionally low overpotential of 166 mV to achieve a current density of 10 mA cm^-2. Moreover, when serving as the anode in PEMWE, the NiRuCoO_<i>x</i> requires 1.72 V to reach a current density of 3A cm^-2, meeting the 2026 target set by the U.S. Department of Energy (DOE: 1.8 V@3A cm^-2). The PEMWE device can operate stably for more than 1500 h with a significantly reduced performance decay rate of 0.025 mV h^-1 compared to commercial RuO₂ (2.13 mV h^-1). This work provides an efficient method for tailoring the octahedron-tetrahedron sites of spinel Co₃O₄, which significantly improves the activity and stability of PEMWE.