NiFeMo Alloy Inverse-Opals on Ni Foam As Outstanding Catalysts for Alkaline Electrolytic Water Splitting

Abstract

Hydrogen, a clean energy carrier with a high gravimetric energy density, is currently most economically produced with steam reforming of natural gases, in which fossil fuels are used as the raw material and CO2 is generated as a side product, both not environmentally sustainable. Renewable energy driven electrocatalytic water splitting is considered the most promising route for future hydrogen production. Its production cost, dominated by the electric energy consumption, however places it in a disadvantageous position, and highly efficient, cost-effective, and durable electrocatalysts, aiming to reduce the necessary working potential for cost competiveness, are critically important for the prevailing of the technology. The present work developed, based on the essential concept of improving quantity and quality of active sites of the catalyst, NiFeMo alloy inverse-opals on nickel foam as an extraordinary catalyst for alkaline electrolytic water splitting, achieving ultralow overpotentials of 33 and 249 mV for the hydrogen evolution reaction (HER) and 198 and 293 mV for the oxygen evolution reaction (OER) at current densities of 10 and 500 mA cm-2, respectively. Ultralow cell voltages of only 1.47 and 1.75 V are enough to deliver current densities of 10 and 500 mA cm-2, respectively, for overall water splitting, outperforming the benchmark couple, Pt/C and IrO2, and state-of-the-art electrolytic water splitting cells. The stability of the product is also outstanding, remaining stable after operations at an ultrahigh current density of 500 mA cm-2 for 50 hours. The success of the product catalyst is attributed to the much increased active site number with the construction of inverse-opals on nickel foam and the much enhanced intrinsic activities of the active sites through synergistic effects between the three constituent elements.