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.

The development of a facile method to construct a high-performance electrode is of paramount importance to the application of alkaline water electrolysis. Here, we report that the activity of nickel foam (NF) towards the oxygen evolution reaction (OER) can be enhanced remarkably through simple immersion in a ferric nitrate (Fe(NO₃)₃) solution at room temperature. During this immersion process, the oxidation of the NF surface by NO₃⁻ ions increases the near-surface concentrations of OH⁻ and Ni²⁺, which results in the in situ deposition of a highly active amorphous Ni-Fe hydroxide (a-NiFeO_xH_y) layer. Specifically, the OER overpotential of the NF electrode decreases from 371 mV (bare NF) to 270 mV (@10 mA·cm⁻² in 0.1 M KOH) after immersion in a 20 mM Fe(NO₃)₃ solution for just 1 min. A longer immersion time results in further increased OER activity (196 mV@10 mA·cm⁻² in 1 M KOH). The overall water splitting properties of the a-NiFeO_xH_y@NF electrode were evaluated using a two-electrode configuration. It is worth noting that the current density can reach 25 mA·cm⁻² in 6 M KOH at an applied voltage of 1.5 V at room temperature.