Bifunctional water splitting enhancement by manipulating Mo-H bonding energy of transition Metal-Mo2C heterostructure catalysts

Abstract

• Ni, Co, Fe-Mo 2 C-coupled in N-doped carbon sheets (TM/Mo 2 C-NCSs) were synthesized. • TM/Mo 2 C-NCSs show boosted bifunctional HER and OER activities and durability. • Optimization of Mo-H Bonding Energy accelerates the desorption of H 2 . • The ternary channels achieve overall fast charge transfer and stable structure. • The vertical growth of TM/Mo 2 C-NCSs on Ni foam aids more active sites exposure. Molybdenum carbide (Mo 2 C) exhibits unique competitive advantages in electrochemical water splitting due to its physicochemical properties. The high intrinsic activity is essential for the high-efficient Mo 2 C catalysts. Herein, transition metal (Ni, Co, or Fe)-Mo 2 C-embedded in N-doped carbon sheets grown on Ni foam (TM/Mo 2 C-NCSs) are synthesized to enhance the intrinsic activity of Mo 2 C by optimizing the Mo-H bonding energy through the interfacial interactions between Ni, Co, or Fe, and Mo 2 C. Owing to the superior intrinsic activity, fast ternary channels, and abundant active sites, the Ni/Mo 2 C-NCSs possess the lowest overpotential for HER (131 mV) and the Fe/Mo 2 C-NCSs show the lowest overpotential for OER (293 mV) at a current density of 100 mA cm −2 in 1 M KOH. The results analyzed with the Density function theory (DFT) calculation indicate that the most superior H adsorption site is at the interface between Mo 2 C and Ni hybrid. H was adsorbed on interface Mo&Ni@Ni/Mo 2 C with proper hydrogen adsorption free energies (ΔG H* ), achieving a fast desorption process in HER. This mechanism is absent in the pristine Mo 2 C catalysts. An alkaline electrolyzer with a cathode of Ni/Mo 2 C-NCSs and anode of Fe/Mo 2 C-NCSs demonstrates a small voltage of 1.66 V at a current density of 100 mA cm −2 . This work offers an elaborated strategy of interface engineering to enhance the intrinsic catalytic activity of Mo 2 C by accelerating H 2 desorption in HER and enhancing the catalytic kinetics of OER simultaneously.