Site-selective Ru doping in spinel Co3O4 unlocks dual-site synergy for acidic water electrolysis

Abstract The development of stable, efficient, and low-cost catalysts for the oxygen evolution reaction (OER) in acidic media, along with a deeper understanding of the underlying reaction mechanisms, remains a central focus in the field of acidic water electrolysis. Herein, catalysts were strategically designed to selectively substitute octahedral and tetrahedral Co sites in Co3O4 with Ru to figure out the role of metal site in different coordination environments for acidic OER activity and stability. By regulating the synthesis strategy and tailoring the crystal coordination environment, we achieved Oct-RuxCo3-xO4 and Tet-RuxCo3-xO4 samples with selective substitution of Ru at octahedral and tetrahedral sites in Co3O4. Experimental and theoretical analysis confirm that Ru substitution at octahedral Co3+ sites activates a dual-metal Ruoct-O-Cooct active center through the oxide path mechanism (OPM) with a reduced energy barrier, whereas tetrahedral substitution disrupts orbital overlap due to excessive atomic spacing. The electron transfer within the Ruoct-O-Cooct configuration effectively suppresses cobalt over-oxidation and dissolution. Consequently, the octahedrally substituted Oct-Ru0.13Co2.87O4 catalyst with only 4 at% Ru exhibits moderate yet promising acidic OER performance, requiring a low overpotential of 240 mV and demonstrating stable operation for over 240 h at 10 mA cm⁻². This performance notably surpasses that of the tetrahedral substituted counterpart, which requires a higher overpotential of 280 mV and sustains stability for only 42 h. This work provides new insights into site-selective substitution strategies in spinel oxides, and establishes a paradigm for designing cost-effective non-precious metal-based catalysts for hydrogen production.