Three-Dimensional Nanoporous Iron Nitride Film as an Efficient Electrocatalyst for Water Oxidation

Exploring efficient and durable catalysts from earth-abundant and cost-effective materials is highly desirable for the sluggish anodic oxygen evolution reaction (OER), which plays a key role in water splitting, fuel cells, and rechargeable metal–air batteries. First-row transition-metal (Ni, Co, and Fe)-based compounds are promising candidates as OER catalysts to substitute the benchmark of noble-metal-based catalysts, such as IrO2 and RuO2. Although Fe is the cheapest and one of the most abundant transition-metal elements, there are seldom papers reported on Fe-only compounds with outstanding catalytic OER activities. Here we propose an interesting strategy by growing iron nitride (Fe3N/Fe4N) based nanoporous film on three-dimensional (3D) highly conductive graphene/Ni foam, which is demonstrated to be a robust and durable self-supported 3D electrode for the OER featuring a very low overpotential of 238 mV to achieve a current density of 10 mA/cm2, a small Tafel slope of 44.5 mV/dec, good stability, and 96.7% Faradaic yield. The high OER efficiency is by far one of the best for single-metal (Fe, Co, and Ni)-based catalysts, and even better than that of the benchmark IrO2, which is attributed to the fast electron transfer, high surface area, and abundant active sites of the catalyst. This development introduces another member to the family of cost-effective and efficient OER catalysts.