CoFe Layered Double Hydroxide Supported on Graphitic Carbon Nitrides: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions

Finding nonprecious metal based highly active and durable bifunctional electrocatalysts for overall water-splitting is essential for the development of various renewable energy storage and conversion technologies. Herein, we report the synthesis of cobalt iron layered double hydroxide (Co1−δFeδ LDH) and g-carbon nitride composite (Co1−δFeδ LDH/g-CNx) for alkaline water electrolysis. The thin Co1−δFeδ LDH nanosheets are successfully impregnated on graphitic carbon nitride surface by one pot co-precipitation method at ambient temperature. The optimal composite, Co0.4Fe0.6 LDH/g-CNx exhibited superior OER activity in 1 M KOH electrolyte with a small overpotential of 0.28 V for 10 mA cm–2, low Tafel slope of 29 mV/dec, 100% faradic efficiency, and high TOF of 0.25 s–1 which is superior to commercial (comm) IrO2. Furthermore, the Co0.4Fe0.6 LDH/g-CNx composite also exhibited remarkable HER activity in alkaline media and its HER activity is slightly lower than that of comm Pt/C at low overpotential but it outperforms Pt/C at high overpotential. The catalyst demonstrated its long-term durability and higher stability for HER and OER under alkaline environment. This Co0.4Fe0.6 LDH/g-CNx catalyst can serve as both cathode and anode for overall water-splitting and required the small potential of 1.61 V to achieve a current density of 10 mA cm–2. The superior electrocatalytic activities of the Co0.4Fe0.6 LDH/g-CNx composite are due to the high electrochemical surface area (ECSA), easy access of abundant active sites, and easy mass transport owing to 2D sheet morphology of the composite.