Mo2C@NC@MoSx porous nanospheres with sandwich shell based on MoO42--polymer precursor for efficient hydrogen evolution in both acidic and alkaline media.

Mo 2 C@NC@MoS x porous nanospheres with sandwich shell have been synthesized for efficient hydrogen evolution in both acidic and alkaline media. Firstly, porous MoO 2 -Mo 2 C@NC nanospheres have been obtained with ultrafine Mo 2 C nanocrystallines as core and ultrathin N-doped carbon (NC) as shell through the carbonization of MoO 4 2- -/aniline-pyrrole (MoO 4 2- -Polymer) as precursor. Secondly, Mo 2 C@NC@MoS x porous nanospheres with sandwich shell have been synthesized by hydrothermal sulfurization, which can be confirmed by XPS and HRTEM. The sandwich shell is composed of ultrathin MoS x , NC layer and Mo 2 C nanocrystallines, which may reduce the strong Mo H bonding energy of pure Mo 2 C and lead to the suitable ΔG H* for HER. In addition, the ultrathin NC can prevent the aggregation of active sites and improve charge transfer rate due to rich N-doping. Mo 2 C@NC@MoS x exhibits enhanced performance and long-time durability in both acidic and alkaline solution. It requires a low onsetpotential of 119 mV, Tafel slope of 56 mV dec −1 in acidic solution and onsetpotential of 86 mV, Tafel slope of 90 mV dec −1 in alkaline solution. Therefore, designing sandwich nanostructure with better conductivity and optimized Mo H bonding energy may be a promising strategy for excellent Mo-based HER electrocatalysts. [ABSTRACT FROM AUTHOR]