Herein, 3D hierarchically porous Co and S co-modificated nickel microsphere arrays developed on nickel foam (NF) substrate (NiCoxSy/NF) are synthesized via a facile template-free electrodeposition protocol in Ethaline-based deep eutectic solvent. The resultant NiCoxSy/NF at optimal incorporating level shows highly efficient electrochemical water splitting performance. The NiCoxSy/NF-based alkaline water electrolyzer requires small cell voltages of 1.57 and 1.63 V to reach 10 and 20 mA cm(-2) overall current densities, sequentially, along with robust durability for over 100 h. Density function theory (DFT) study indicates that the synergistic actions induced by the dual-incorporation of Co and S, enabling to optimize the binding energies for water dissociation, hydrogen adsorption/desorption as well as the oxygen-containing intermediates. The NiCoxSy/NF manifests excellent electrocapacitive performance with high capacitance (4964 mF cm(-2) at 5 mA cm(-2)) and well cycling stability (0.4% decay after 5000 cycles) being an electrode material for supercapacitor application. Particularly, an all-solid-state symmetric supercapacitor based on NiCoxSy/NF yields high energy density (48.46 Wh kg(-1) at 500 W kg(-1)) with superior cycling durability (6.2% decay after 10,000 cycles). This study contributes a facile path for the synthesis of hierarchically porous materials and highlights the effect of multielement synergistic modulation to boost the electrochemical activity.