Fe-doped NiO mesoporous nanosheets array for highly efficient overall water splitting

Great efforts in developing bifunctional water splitting electrocatalysts are to construct catalytic materials with new and optimized chemical compositions and structures for enhancing efficiency of both anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). In this work, the Fe-doped NiO mesoporous nanosheets array on Ni foam with different Fe dopant content (Fex%-NiO/NF) was synthesized by a facile solvothermal synthesis in mixed solvents of deionized water and methanol and subsequent anneal in air. The well-connected three-dimensional mesoporous nanosheets array structure offers a large number of catalytically active sites and buffers the large volume change during the electrochemical process of OER and HER. More importantly, the doped Fe3+ ions modified atomic and electronic structure of NiO by activated Ni centers through a Fe-induced partial-charge-transfer process which can promote the electrocatalytic performances of NiO for OER and HER. As a result, the optimized Fe11%-NiO/NF electrode exhibited excellent OER activity with a small overpotential of 206 mV at 10 mA cm−2 and a low Tafel slope of 49.4 mV dec−1. Moreover, it also presented prominent HER activity, only demanding a small overpotential of 88 mV at 10 mA cm−2 and a low Tafel slope of 49.7 mV dec−1. A two-electrode electrolyzer using Fe11%-NiO/NF as both anode and cathode performs active overall water splitting, needing a small cell voltage of 1.579 V to afford a current density of 10 mA cm−2. This work can stimulate the design and optimization of Ni-Fe mixed oxide as an efficient electrocatalyst for practical overall water electrolysis.