The sluggish four-electron transfer of the oxygen evolution reaction(OER)limits the performance of water electrolyzers.Hence,OER electrocatalysts based on earth-abundant elements are urgently needed.Heteroatom doping has been an efficient approach to boost the intrinsic OER activity of the active sites by modifying the electronic structure.Here,a simple anion substitution strategy is reported that increases the OER activity of nickel selenides via a one-step hydrothermal treatment of a metal-organic framework precursor.The resulting S-substituted Ni3Se4 nanoparticles display distortion of their crystal lattice.As expected,the sulfur substitution modifies the electronic structure of Ni3Se4 and leads to outstanding elec-trocatalytic activity.All the S-substituted Ni3Se4 catalysts exhibit higher OER activities than the original Ni3Se4.The optimized catalyst achieves a current density of 10 mA cm-2 at an overpotential of 275 mV with a Tafel slope of 64 mV dec-1 in 1.0 M KOH.In addition to its electrochemical activity,the S-Ni3Se4-2 catalyst also exhibits good stability with only a 7.5％increase in overpotential at 50 mA cm-2 after 100 hours.This work demonstrates one strategy to modify the electronic structure of transition metal com-pounds by anion regulation.