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 CoO and exploited the synergism between the tetrahedron and octahedron sites by partially substituting Co with Ni and Ru (denoted as NiRuCoO), 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 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 catalyst exhibits an exceptionally low overpotential of 166 mV to achieve a current density of 10 mA cm. Moreover, when serving as the anode in PEMWE, the NiRuCoO requires 1.72 V to reach a current density of 3A cm, meeting the 2026 target set by the U.S. Department of Energy (DOE: 1.8 V@3A cm). The PEMWE device can operate stably for more than 1500 h with a significantly reduced performance decay rate of 0.025 mV h compared to commercial RuO (2.13 mV h). This work provides an efficient method for tailoring the octahedron-tetrahedron sites of spinel CoO, which significantly improves the activity and stability of PEMWE.