Facile Preparation of Ultrathin Co3 O4 /Nanocarbon Composites with Greatly Improved Surface Activity as a Highly Efficient Oxygen Evolution Reaction Catalyst.

The efficient catalytic oxidation of water to dioxygen plays a significant role in solar fuel and artificial photosynthetic systems. It remains highly challenging to develop oxygen evolution reaction (OER) catalysts with high activity and low cost under mild conditions. Here, a new composite material is reported based on ultrathin 2D Co3 O4 nanosheets and reduced graphene oxides (rGO) by means of a one-pot hydrothermal strategy. The ultrathin Co3 O4 /rGO nanocomposite shows superior stability under alkaline conditions and exhibits an overpotential of 290 mV with a Tafel slope of 68 mA dec-1 , which is much smaller than that of bare Co3 O4 catalyst. Extensive experiments were also carried out using 0D CS and 1D CNTs (CS=carbon spheres, CNTs=carbon nanotubes) in place of the 2D rGO. The overpotentials of as-prepared nanocomposites decrease with the increase of the dimension of nanocarbons, suggesting the electrochemistry activity is closely related to the surface area of carbon substrates. In addition, compared with ultrathin 2D Co3 O4 nanosheets with a Co2+ /Co3+ ratio of 1.2, the as-prepared ultrathin Co3 O4 /rGO nanocomposite with a Co2+ /Co3+ ratio of 1.4 contributes to the better OER performance as more oxygen vacancies can be formed in the ultrathin Co3 O4 /rGO nanocomposite under the experimental conditions. Compared with other Co3 O4 -containing composite materials reported so far, the ultrathin Co3 O4 /rGO nanocomposites show excellent OER performance.