One-Step Synthesis of Highly Active NiFe Electrocatalysts for the Oxygen Evolution Reaction.

Electrochemical water splitting is a key technology for the conversion of renewable energy into chemical resources such as hydrogen. However, the oxygen evolution reaction (OER), a half-reaction of water splitting, is so slow that various effective catalysts for the OER have been explored. In this study, we demonstrate a simple and direct process for the synthesis of OER-active NiFe catalysts over electrodes. A NiFe/C catalyst layer was formed on a glassy carbon electrode by simply dropping the catalyst ink containing only metal nitrates and carbon black. The catalyst layer exhibited higher OER performance than the state-of-the-art Ir/C catalyst. The presence of carbon black is essential to enhance the OER activity of NiFe because carbon black helps to disperse the NiFe active sites. Cyclic voltammetry indicated that Ni and Fe are adjacent to each other on the surface of carbon black, resulting in significantly higher activity of NiFe/C compared to those of Ni/C and Fe/C. The effects of the Ni/Fe ratio, amount of carbon black, and type of carbon black on the OER activity of NiFe/C were examined in detail. Furthermore, we discuss the factors that determine the OER performance of NiFe/C.