Structural engineering of Fe-doped Ni2P nanosheets arrays for enhancing bifunctional electrocatalysis towards overall water splitting

Highlights: • By regulating the phosphorization conditions, the Fe-doped Ni₂P nanosheets arrays with different surface roughness can be obtained. • The as-prepared Fe-doped Ni₂P nanosheets arrays with slightly rough surface exhibit low overpotentials (η₁₀₀) of 213 and 210 mV for OER and HER. • The designed principle is to increase the electrochemical active sites by combining the control of surface structural conditions and the incorporation of Fe atoms, thus inducing the enhanced bifunctional electrocatalytic activity. • The assembled water electrolyzer using this bifunctional electrocatalysts only needs a low cell voltage. The 3D nanosheets arrays architecture, coupled with the modulation of surface structure and the incorporation of foreign atoms, constructs an anticipated method to boost the electrocatalytic performance on the transition metal compounds-based non-precious catalysts. Herein, we report a structural engineering strategy of Fe-doped Ni₂P nanosheets arrays supported on Ni foam for enhancing electrocatalytic performance of both oxygen evolution (OER) and hydrogen evolution (HER) reactions. Benefitting from the increased electrochemical active sites caused by structural engineering and the strong electronic effect derived from Fe-doping, the Fe-doped Ni₂P nanosheets arrays with slightly rough surface can achieve the highest OER activity with a low overpotential of 213 mV at a current density of 100 mA cm⁻² and a Tafel slope of 50.7 mV dec^–1, better than the other catalysts with different surface structures. Moreover, the enhanced HER performance can also be obtained based on this distinct structure. Finally, a two-electrode alkaline electrolyzer, applying this optimized bifunctional catalyst as both the cathode and anode, can be driven with a low cell voltage of 1.54 V to afford a current density of 10 mA cm⁻², as well as excellent stability. The present study bridges the gap between structural engineering and bifunctional electrocatalytic activity towards overall water splitting, and opens up a new avenue for the material designs of high-performance nanoarrays electrocatalysts.