Heteroatom doping has emerged as an effective strategy to enhance the performance of electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Traditional doping methods often involve harsh chemical treatments and tedious procedures, hindering their widespread applications. Furthermore, although dynamic surface reconstruction in alkaline media is commonly observed in bimetallic compounds, strategies to regulate this reconstruction behavior for enhanced HER and OER performances remain inadequately explored. Herein, we report an ultrafast (≤ 300s) and mild electrochemical doping approach to fabricate Se-doped NiCo₂S₄ hollow nanoarrays on carbon fiber papers (a-NiCo₂(S_1-xSe_x)₄), investigating the role of Se in enhancing overall water splitting performance. Under HER conditions, a-NiCo₂(S_1-xSe_x)₄ demonstrates remarkable stability, with Se tuning the electronic structure to optimize intermediate adsorption and facilitate H₂O dissociation. While under OER conditions, Se doping lowers the energy barrier for reconstruction and promotes transformation into active Se, S co-doped Ni_0.33Co_0.67OOH nanosheets. The optimal samples exhibit superior HER and OER activity, requiring a cell voltage of 1.578 V to deliver a current density of 100 mA cm⁻² for overall water splitting. This work not only introduces a facile method for Se doping but also provides comprehensive insights into the structure–composition–activity relationship for Se-doped bimetallic sulfide.