Evaluation of electrosynthesized reduced graphene oxide - Ni-, Fe-, Co-based (oxy)hydroxide catalysts toward oxygen evolution reaction

In this work, the effect of the addition of graphene oxide (GO) to nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxide/hydroxide/(oxy)hydroxide catalysts on their morphological, structural, and oxygen evolution reaction (OER) catalytic activity is investigated. The catalysts are fabricated during two-step electrodeposition: the first step includes the deposition of GO flakes, which in the second step become reduced with simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO are fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. Different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone, however it was reduced in comparison with the CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies show that each of the catalysts has a specific role in influencing the process: the improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.