Hollow tubular Co3S4/NiS/FeS as high-efficiency tri-functional electrocatalyst for Zn-air battery and overall water splitting

In this paper, a hollow tubular Co3S4/NiS/FeS heterogeneous composite was prepared by an ordinary hydrothermal procedure. The inner Co3S4 can act as the carrier of the outer NiS/FeS, and the outer NiS/FeS can effectively prevent the collapse of the inner Co3S4 hollow structure, ensuring the durability of the structure and performance in the cyclic charge-discharge test. The strong electronic interaction between Co3S4 and NiS/FeS significantly improves the catalytic activity. It shows a small 230 mV overpotential at 10 mA cm−2, which is superior to commercial RuO2. The Zn-air battery assembled with Co3S4/NiS/FeS catalyst showed outstanding stability over 2700 cycles with a narrow voltage gap of 0.67 V at 3 mA cm−2. Flexible battery also combined based on this catalyst can generally be discharged/charged at each bending angle and the gap remained almost continuous. Furthermore, Co3S4/NiS/FeS also displays hydrogen evolution reactions activity, displaying a lower overpotential of 233 mV at 10 mA cm−2. In the overall water splitting, Co3S4/NiS/FeS is used as both anode and cathode electrocatalyst, which can reach 10 mA cm−2 at 1.52 V, and the performance remains steady for 50 h. In conclusion, Co3S4/NiS/FeS is a potential tri-functional catalyst for ZABs and overall water splitting.