In situ addition of graphitic carbon into a NiCo2O4/CoO composite: enhanced catalysis toward the oxygen evolution reaction†
We present a rapid, environmentally benign one-pot synthesis technique for the production of a NiCo2O4/CoO and graphite composite that demonstrates efficient electrocatalysis towards the Oxygen Evolution Reaction (OER), in 1.0 M KOH. The NiCo2O4/CoO/graphitic carbon composite that displayed optimal OER catalysis was synthesized by nitrate decomposition in the presence of citric acid (synthesized glycine and sucrose variants displayed inferior electro kinetics towards the OER). Screen-printed electrodes modified with ca. 530 μg cm−2 of the citric acid NiCo2O4/CoO/graphite variant displayed remarkable OER catalysis with an overpotential (η) of +323 mV (vs. RHE) (recorded at 10 mA cm−2), which is superior to that of IrO2 (340 mV) and RuO2 (350 mV). The composite also exhibited a large achievable current density of 77 mA cm−2 (at +1.5 V (vs. RHE)), a high O2 turnover frequency of 1.53 × 10−2 s−1 and good stability over the course of 500 repeat cycles. Clearly, the NiCo2O4/CoO composite has the potential to replace precious metal based catalysts as the anodic material within electrolysers, thereby providing a reduction in the associated costs of hydrogen production via water splitting.