Cd doped Ni3S2 nanosheet arrays grown on nickel foam as highly efficient and robust bifunctional electrocatalysts for alkaline overall water splitting

Stable and highly efficient electrocatalysts are very important for water splitting. Introducing exogenous elements can alter the structure of the catalysts, thus improving the electrocatalytic activity. In this study, via a facile hydrothermal strategy and Cd/Ni ratio tuning, Cd-doped Ni3S2 nanosheet arrays grown on Ni foam (Cd-Ni3S2/NF-x) are fabricated. The optimized Cd-Ni3S2/NF-1/4 exhibits the best electrocatalytic performance in alkaline media (1 M KOH) due to the higher electroconductivity and more accessible active sites. At a current density of 10 mA cm-2, ultralow overpotentials of 140 and 197 mV are required for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. During overall water splitting, a two-electrode electrolyzer of Cd-Ni3S2/NF-1/4 was used to achieve a low cell voltage of 1.54 V with ultralong-term durability ≥ 50 h. Introducing Cd into Ni3S2 leads to Ni→S electron transfer, thus increasing the Ni3+ content, which is beneficial to the increased OER activity. Density functional theory (DFT) calculations demonstrate that Cd-doped Ni3S2 has a reduced Gibbs free energy of hydrogen adsorption (∆GH*) in the HER and a decreased energy barrier of rate determination in the OER, contributing to the improved overall water-spitting performance. This work offers an effective strategy by virtue of element doping to fabricate highly effective bifunctional electrocatalysts to realize mass production of hydrogen.