An efficient and robust noble-metal-free self-standing bifunctional water electrolysis catalyst: Co3S4@Ex.NiFe-LDH for alkaline water electrolysis

Abstract

Electrolysis of water integrated with the renewable energy as input source can contribute significantly in the production of green hydrogen, a clean and versatile energy carrier. In water electrolyzer, the hydrogen evolution reaction (HER) at the cathode must act synchronously with the oxygen evolution reaction (OER) at the anode to effectively accomplish total water-splitting. The performance of an electrolyzer is often limited by the low performance of anode and it is important to develop an electrocatalyst which can efficiently perform both HER and OER. Ni and Fe based layered-double-hydroxides (LDHs) have gained a lot of interest owing to their outstanding OER electrocatalytic activity, however they are known to have poor HER performance. To enhance the overall water splitting efficiency of the LDHs, we present a simple approach of preparing a heterojunction of LDH with cobalt sulphide. The bifunctional electroactivity of the designed electrocatalyst Co3S4@Ex.NiFe-LDH, worked efficiently in both HER and OER electrocatalysis. Chalcogenides known for HER, not only improves the HER performance of the composites but also found to reduce the charge transfer resistance. Obtained results showed that when it comes to the OER performance, the recommended catalyst shadows the state of art catalyst RuO2. Additionally, the catalyst has outstanding activity and stability, achieving a current density of around −120 mA/cm2 over a six-day period. The electrolyzer composed of both anode and cathode designated as Co3S4@Ex.NiFe-LDH||Co3S4@Ex.NiFe-LDH only needs a low voltage input of 1.49 V to achieve a total water splitting reaction at required current density of 10 mA/cm2, showing efficacy at the low voltage input. Experimental observations showed Co3S4@Ex.NiFe-LDH performs better than Pt/C–RuO2 in alkaline water electrolysis. The electrolyzer can continuously produce hydrogen at 50 mA/cm2 for more than a week period; indicating its potential for long-term application.