3D Porous Cobalt–Iron–Phosphorus Bifunctional Electrocatalyst for the Oxygen and Hydrogen Evolution Reactions

A 3D porous Co–Fe–P foam fabricated using electrodeposition is presented as a high-performance and durable catalyst for both oxygen and hydrogen evolution reactions. To establish optimal Fe/Co ratio of the catalyst, Co–Fe–P films were electrodeposited with Fe/Co ratio of 0.2, 0.4, 1.1, and 3.3. Among the prepared samples, the Co–Fe–P film with the Fe/Co ratio of 1.1 (Co–Fe–P-1.1) exhibited the highest activity for the oxygen evolution reaction, which could be attributed to the transfer of the valence electron from Co to Fe and P. To improve performance of the Co–Fe–P-1.1, a 3D porous foam structure was adopted using the electrodeposition. The Co–Fe–P foam had 94 times larger electrochemical active surface area (ECSA) than the Co–Fe–P film with similar Fe/Co ratios of 1.1, resulting in an distinguished activity for the oxygen evolution reaction (294 mV at 10 mA/cm2) and hydrogen evolution reaction (73 mV at 10 mA/cm2) in an alkaline solution. Since the electrodeposited Co–Fe–P foam itself can be directly used as an electrode, it is free from binders, and microstructure of the electrode can be engineered by controlling the electrodeposition condition, leading to the enlarged ECSA and improved performance. Thus, the Co–Fe–P foam presented in this study offers a facile and controllable synthesis of catalyst and electrode through an easy electrodeposition process.