Ultra-fast synthesis of transition metal-MXene nanocomposite electrocatalyst for energy-saving seawater hydrogen production: Experiment and theory

Switching from the urea oxidation reaction (UOR) to the oxygen evolution reaction (OER) is a beneficial way to lower the amount of energy needed to make hydrogen gas during the hydrogen evolution reaction (HER). Due to the sluggish reaction kinetics of the six electrons reaction of UOR, designing a privileged bifunctional electrocatalyst for both HER and UOR necessitates. The 2D nano-sized non-noble metal electrocatalysts make it possible to speed up reactions and improve their electrocatalytic performance. We synthesized nickel-cobalt-MXene composite nanosheets (NiCoMXene) on the surface of copper foam using a one-pot, simple, and ultra-fast electrochemical method. This 2D electrocatalyst demonstrates high electrocatalytic performance towards HER (overpotential of 76 mV at-10 mA cm- 2 ) with excellent durability in alkaline media. Furthermore, NiCoMXene nanocomposite served as a bifunctional electrocatalyst to investigate hydrogen gas production by a hybrid system HER coupled with UOR in seawater. The NiCoMXene requires a low overpotential for HER (81 mV) and UOR (1.38 V) to achieve a current density of 10 mA cm- 2 in seawater, and the needed cell voltage to reach the same current density is 1.42 V in seawater. Our DFT analysis found a significant synergy between MXene and NiCo in the electrocatalyst. PDOS analysis showed remarkably that introducing Ni atoms to MXene shifts the dband center to the left (lower energy), while Co atoms shifts it to the right (higher energy) and increased states near the Fermi level. This electronic structure makes the nanocomposite an ideal electrocatalyst, with MXene providing electrons and Co atoms serving as active sites for both HER and UOR. This research work can provide a useful directive to explore the electrocatalysts with outstanding catalytic activity.