CoFe-layered double hydroxide nanosheet arrays directly grown on reduced graphene oxide modified Ni foam for overall water splitting

The over-exploitation of fossil fuels has led to the destruction of ecosystems, the global energy crisis, climate warming and the greenhouse effect, and other thorny problems. Therefore, the development and utilization of an environmentally friendly and renewable energy source to replace traditional fossil fuel is vital to the sustainable development of the economy and society. Needless to say, electrochemical water splitting is a commercial technology with great potential to obtain environmentally friendly and sustainable energy. CoFe-LDH (layered double hydroxide) nanosheets arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were rationally designed and synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) composites all show Co_xFe₁-LDH nanosheets grown on the surface of rGO/NF. The electrochemical results show that all the Co_xFe₁-LDH/rGO/NF composites possess high electrocatalytic activity. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 mV and 105 mV at 10 mA cm^-2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Excellent electrical catalytic performance of the catalysts Co₃Fe₁-LDH/rGO/NF is due to the Co-Fe synergistic effect and the present nanosheet arrays structure with open channels exposing of numerous active sites, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing the electrochemical performance along with improved electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF being beneficial to the gas bubble release and greatly enhancing the long-term electrochemical stability. The present citric acid-assisted aqueous phase coprecipitation method can be used to fabricate other kinds of non-precious transition metal composite catalysts as highly effective catalysts for the development of clean and renewable energy equipment.