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

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.