Cobalt-modified rhenium disulfide nanosheets rich in defects, obtained by following an ingenious atom substitution strategy, exhibited boosted HER performance. The 2%-Co doped ReS₂ sample was highly efficient in both acid electrolyte (149 mV) and alkaline electrolyte (240 mV), achieving a current density of 10 mA cm⁻² as well as superior long-term durability.