Controllable Synthesis of Ordered Mesoporous Mo2C@Graphitic Carbon Core-Shell Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution.

Mo2C is a possible substitute to Pt-group metals for electrocatalytic hydrogen evolution reaction (HER). Both support-free and carbon-supported Mo2C nanomaterials with improved HER performance have been developed. Herein, distinct from prior research, novel ordered mesoporous core-shell nanowires with Mo2C cores and ultrathin graphitic carbon (GC) shells are rationally synthesized and demonstrated to be excellent for HER. The synthesis is fulfilled via a hard-templating approach combining in situ carburization and localized carbon deposition. Phosphomolybdic acid confined in the SBA-15 template is first converted to MoO2, which is then in situ carburized to Mo2C nanowires with abundant surface defects. Simultaneously, GC layer (the thickness is down to ∼1.0 nm in most areas) is controlled to be locally deposited on the Mo2C surface because of its strong affinity with carbon and catalytic effect on graphitization. Removal of the template results in the Mo2C@GC core-shell nanowire arrays with the structural properties well-characterized. They exhibit excellent performance for HER with a low overpotential of 125 mV at 10 mA cm-2, a small Tafel slope of 66 mV dec-1, and an excellent stability in acidic electrolytes. The influences of several factors, especially the spatial configuration and relative contents of the GC and Mo2C components, on HER performance are elucidated with control experiments. The excellent HER performance of the mesoporous Mo2C@GC core-shell nanowire arrays originates from the rough Mo2C nanowires with diverse active sites and short charge-transfer paths and the ultrathin GC shells with improved surface area, electronic conductivity, and stabilizing effect on Mo2C.