Approaching the activity limit of CoSe₂ for oxygen evolution via Fe doping and Co vacancy

Electronic structure engineering lies at the heart of efficient catalyst design. Most previous studies, however, utilize only one technique to modulate the electronic structure, and therefore optimal electronic states are hard to be achieved. In this work, we incorporate both Fe dopants and Co vacancies into atomically thin CoSe₂ nanobelts for /coxygen evolution catalysis, and the resulted CoSe₂-D_Fe-V_Co exhibits much higher catalytic activity than other defect-activated CoSe₂ and previously reported FeCo compounds. Deep characterizations and theoretical calculations identify the most active center of Co₂ site that is adjacent to the V_Co-nearest surface Fe site. Fe doping and Co vacancy synergistically tune the electronic states of Co₂ to a near-optimal value, resulting in greatly decreased binding energy of OH* (ΔE_OH) without changing ΔE_O, and consequently lowering the catalytic overpotential. The proper combination of multiple defect structures is promising to unlock the catalytic power of different catalysts for various electrochemical reactions.