Cobalt Spinel Nanocubes on N-Doped Graphene: A Synergistic Hybrid Electrocatalyst for the Highly Selective Reduction of Carbon Dioxide to Formic Acid

Carbon dioxide reduction into useful chemical products is a key technology to address urgent climate and energy challenges. In this study, a nanohybrid made by Co3O4 and graphene is proposed as an efficient electrocatalyst for the selective reduction of CO2 to formate at low overpotential. A comparison between samples with different metal oxide to carbon ratios and with or without doping of the graphene moiety indicates that the most active catalyst is formed by highly dispersed and crystalline nanocubes exposing {001} oriented surfaces, whereas the nitrogen doping is critical to obtain a controlled morphology and to facilitate a topotactic transformation during electrocatalytic conditions to CoO, which results in the true active phase. The nanohybrid made up by intermediate loading of Co3O4 supported on nitrogen-doped graphene is the most active catalyst, being able to produce 3.14 mmol of formate in 8 h at -0.95 V vs SCE with a Faradaic efficiency of 83%.