Electrical and Structural Optimization of Nickel Sulfide Nano-Flower by Mn Modulation as Robust Bifunctional Electrocatalyst for Overall Water Splitting

Designing an efficient and low-cost bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte is still very important and challenging. Herein, using a simple hydrothermal and sulfidation annealing method, nanoflower-like Mn-NiS with regular morphology was grown in situ on the surface of nickel foam. Through the detailed analysis of X-ray photoelectron spectroscopy results, it is found that the successful doping of Mn2+ can effectively adjust the electronic structure of NiS. As we envisioned, the prepared Mn-NiS shows only 99 mV overpotential and 64.8 mV dec−1 Tafel slope in HER at 10 mA cm−2 and has only 320 mV and 65.5 mV dec−1 in OER at 50 mA cm−2. In addition, the alkaline electrolytic cell composed of Mn-NiS double electrodes has a cell-voltage of only 1.54 V at 10 mA cm−2, and maintains good stability. More importantly, the results of density functional theory calculations show that after Mn2+ successfully changes the electronic structure on the NiS surface, it not only promotes the HER kinetics, but also greatly increases the OER activity.