Fabrication of Nanoporous Nickel-Iron Hydroxylphosphate Composite as Bifunctional and Reversible Catalyst for Highly Efficient Intermittent Water Splitting.

Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO/NF electrodes can obtain the current densities of 20 and 100 mA cm at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.