Defined organic-octamolybdate crystalline superstructures derived Mo2C@C as efficient hydrogen evolution electrocatalysts

Hydrogen evolution electrocatalysts derived from metal-organic crystalline frameworks can inherit the merits of ordered and adjustable structures with high surface area. In this paper, organic-octamolybdate crystalline superstructures (OOCS) with a fixed stoichiometric ratio of Mo8(L)2 and high Mo content (> 40 wt%) were synthesized using flexible ligands with controllable lengths (named as OOCS-1-3). Then, molybdenum carbides coated with carbon layers as electrocatalysts (Mo2C@C-1-3) can be obtained directly from a one-step high-temperature carbonization process using OOCS-1-3 as precursors. As a typical example, Mo2C@C-3 exhibits satisfactory hydrogen evolution activity with a low overpotential of 151 mV (1.0 mol/L KOH) at 10 mA/cm2 and stability for 24 h. The electrocatalytic activity is mainly from the synergistic interactions between the carbon layers and molybdenum carbide species. Furthermore, compared with the initial content of C, N, Mo in OOCS and Mo2C@C, the catalytic activity increases with the N amount. This work makes organic-octamolybdate crystalline superstructures used as general precursors to product high Mo content electrocatalysts applied in energy storage and conversion fields.