Boosting overall water splitting by incorporating sulfur into NiFe (oxy)hydroxide

Developing highly active and cost-effective electrocatalysts for enhancing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a significant challenge for overall water splitting. Sulfur-incorporated nickel iron (oxy)hydroxide (S-NiFeOOH) nanosheets were directly grown on commercial nickel foam using a galvanic corrosion method and a hydrothermal method. The incorporation of sulfur into NiFeOOH enhanced the catalytic activity for the HER and OER in 1 M KOH electrolyte. The enhanced catalytic activity is attributed to the change in the local structure and chemical states due to the incorporation of sulfur. High performance for overall water splitting was achieved with an alkaline water electrolyzer. This was realized by employing S-NiFeOOH as a bifunctional electrocatalyst, thereby outperforming a water electrolyzer that requires the usage of precious metal electrocatalysts (i.e., Pt/C as the HER electrocatalyst and IrO2 as the OER electrocatalyst). Moreover, when driven by a commercial silicon solar cell, an alkaline water electrolyzer that uses S-NiFeOOH as a bifunctional electrocatalyst generated hydrogen under natural illumination. This study shows that S-NiFeOOH is a promising candidate for a large-scale industrial implementation of hydrogen production for overall water splitting because of its low cost, high activity, and durability. In addition, the solar-driven water electrolyzer using S-NiFeOOH as a bifunctional electrocatalyst affords the opportunity for developing effective and feasible solar power systems in the future.