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

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 fieldof acidic water electrolysis. Herein, catalysts were strategically designed to selectively substitute octahedral andtetrahedral Co sites in Co3O4 with Ru to figure out the role of metal site in different coordination environmentsfor acidic OER activity and stability. By regulating the synthesis strategy and tailoring the crystal coordinationenvironment, we achieved Oct-RuxCo3-xO4 and Tet-RuxCo3-xO4 samples with selective substitution of Ru atoctahedral and tetrahedral sites in Co3O4. Experimental and theoretical analysis confirm that Ru substitution atoctahedral 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 atomicspacing. The electron transfer within the Ruoct-O-Cooct configuration effectively suppresses cobalt over-oxidationand dissolution. Consequently, the octahedrally substituted Oct-Ru0.13Co2.87O4 catalyst with only 4 at% Ru exhibitsmoderate yet promising acidic OER performance, requiring a low overpotential of 240 mV and demonstratingstable operation for over 240 h at 10 mA cm⁻². This performance notably surpasses that of the tetrahedralsubstituted counterpart, which requires a higher overpotential of 280 mV and sustains stability for only 42 h. Thiswork provides new insights into site-selective substitution strategies in spinel oxides, and establishes a paradigmfor designing cost-effective non-precious metal-based catalysts for hydrogen production.