Symmetric-Waveform Alternating-Current Excitation Enables Full Ni Valence-State Transformation in Co-Ni Catalysts

The oxygen evolution reaction (OER) is limited by the difficulty of achieving complete oxidation of transition metals to higher valence states, restricting the utilization of their intrinsic activity. Conventional direct-current polarization typically produces mixed-valence surfaces with only partial enrichment of Ni³⁺ and Co³⁺. Here, we report a symmetric-waveform alternating-current activation strategy that induces dynamic surface reconstruction, enabling full conversion of Ni²⁺ into Ni³⁺ and partial oxidation of Co²⁺ into Co³⁺. Experimental characterization confirms the enrichment of high-valence species, while density functional theory calculations reveal that a fully trivalent Ni surface shifts the rate-determining step from *OH adsorption to *OOH adsorption with a reduced barrier. Projected density of states analysis shows Ni d-band centers approaching the Fermi level, facilitating stronger orbital interactions with oxygen intermediates. Charge distribution analyses further indicate enhanced conductivity and electron redistribution. These synergistic effects lower the overpotential at 10 mA cm^-2 by 63.6 mV and increase catalytic activity by 12.5%. This work establishes dynamic valence-state engineering via alternating-current activation as a pathway for designing noble-metal-free, high-performance OER catalysts for sustainable hydrogen production.