Ultrathinning Nickel Sulfide with Modulated Electron Density for Efficient Water Splitting

Developing nonprecious electrocatalysts via a cost-effective methods to synergistically achieve high active sites exposure and optimized intrinsic activity remains a grand challenge. Here a low-cost and scaled-up chemical etching method is developed for transforming nickel foam (NF) into a highly active electrocatalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The synthetic method involves a Na2S-induced chemical etching of NF in the presence of Fe, leading to a growth of ultrathin Fe-doped Ni(3)S(2)arrays on the NF substrate (FexNi3-xS2 @ NF). The combined experimental and theoretical investigations reveal that the incorporated Fe cations significantly modulate the morphology and the surface electron density of Ni3S2, and thus significantly boost the electrochemically active surface area, electron transfer, and optimize the hydrogen/water absorption free energy. The developed Fe0.9Ni2.1S2 @ NF requires overpotentials of only 72 mV at 10 mA cm(-2)for HER and 252 mV at 100 mA cm(-2)for OER in 1.0mKOH, respectively, enabling an alkaline electrolyzer at a low cell voltage of 1.51 V to drive 10 mA cm(-2)for overall water splitting. More broadly, this synthetic approach is very versatile and can be used to synthesize other ultrathin metal sulfides (e.g., Fe-Cu-S, Fe-Al-S, and Fe-Ti-S).