Carbon wrapped bimetallic NiCo nanospheres toward excellent HER and OER performance

The development of highly efficient and low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) dual-functional catalysts is one of the key issues in the energy conversion system of water splitting. In this work, the carbon wrapped bimetallic NiCo nanospheres were prepared via a simple annealing process. Furthermore, the effect of different molar ratio of Ni:Co on the electrocatalytic properties of the obtained samples were investigated. Among these obtained catalysts, sample (with the molar ratio of Ni:Co was 1:2) exhibited the best electrocatalytic performance both for HER and OER. Electrochemical analysis showed that the overpotentials were only 105 and 330 mV for HER and OER to reach a catalytic current density of 10 mA cm−2, respectively. The corresponding Cdl (electric double-layer capacitance) value can reach up to 17.1 mF cm−2. What is more, the I-t-tests were carried out to prove its superior long-term catalytic durability. It was demonstrated that the excellent properties of HER and OER can be attributed to the large Cdl of the sample, the optimized molar ratio of NiCo alloy as well as the improved stability and electron transfer efficiency via carbon coating. The schematic diagrams have been provided to better understand the possible formation process and electrocatalytic mechanism. In brief, this work could provide a feasible and simple route for the design of bimetallic-based electrode materials toward superior HER and OER performance.