To enter the era of a clean and sustainable hydrogen economy, it is crucial to first discover non-noble metal electrocatalysts that can be used for oxygen evolution reactions (OER) of water electrolyzers. Herein, we demonstrate highly active and durable Co- and Sn-co-doped Ni3S2 catalysts supported on Ni foam (CoSn-Ni3S2@NF) for the OER in alkaline media. Benefiting from the hierarchically porous nanosheet morphology and synergistic strong electron interaction among Co, Sn, and Ni ions, the CoSn-Ni3S2@NF achieves outstanding OER activity in 1 M KOH with a low overpotential of 321 mV at a current density of 0.2 A cm−2. Furthermore, the CoSn-Ni3S2@NF alkaline water electrolysis cell shows a significantly high current density of 1.367 A cm−2 at a cell voltage of 2.0 V under 80 °C and 30 wt% KOH condition using a nickel–iron layered double hydroxide for the hydrogen evolution reaction and a Zirfon PERL separator (500 μm). Based on the defect formation energy and electronic structure obtained using density functional theory calculation, the enhanced intrinsic activity of CoSn-Ni3S2@NF can be attributed to the Co and Sn dopants with S vacancies, which increase activation sites (and free electrons) and favorably modify the Ni 3d-band center to be closer to the Fermi level. This work not only demonstrates a highly electrocatalytic active OER catalyst for water electrolyzers, but also provides a new design principle that can be used for high performance materials by tailoring the electronic structure of transition and post transition metal ions.