Herein, the ultrafine molybdenum carbide/nitride (Mo 2 C/Mo 2 N) heterojunction loaded by nitrogen (N), phosphorus (P)-codoped carbon matrix with hierarchical porous (PNC) is prepared in-situ by fabricating the ternary complex of silica (SiO 2 ) nanoparticles, chitosan (CS) and phosphomolybdic acid (PMo 12 ) as precursor, followed by annealing and hydrofluoric acid (HF) etching. Due to the excellent structural characteristics of the optimized catalyst Mo 2 C/Mo 2 N@PNC-8-2, including the Mo 2 C/Mo 2 N heterojunction and its uniform dispersion in PNC, P-doping in Mo 2 C/Mo 2 N, Mo vacancies, the strong interface coupling between Mo 2 C/Mo 2 N heterojunctions and PNC, as well as the connected macroporous channels and hierarchical porous structure, etc., not only large numbers of active sites are exposed, but also the electron density distribution around Mo atoms is tuned. Therefore, the charge/mass transport is greatly improved, resulting in the more superior hydrogen evolution activity of Mo 2 C/Mo 2 N@PNC-8-2 than that of the single-phased Mo 2 C or Mo 2 N counterpart, with lower overpotentials of 62 or 97 mV to achieve10 mA cm −2 in alkaline or acidic solution, respectively. Moreover, Mo 2 C/Mo 2 N@PNC-8-2 still shows excellent long-term durability. This study opens up a new idea for designing highly efficient electrocatalysts via integrating heterojunction, defects, heteroatom doping, and hierarchical porous structure.
The rational design and facile synthesis of transition metal-based catalysts supported by carbon nanomaterials with high activity, selectivity and stability remain a great challenge. Recently, the low-cost, stable and high-performance electrocatalysts for efficient oxygen evolution reaction (OER) derived from porous metal-organic framework (MOF) precursors have attracted numerous attention. Herein, a new type of CoMo carbide/nitride embedded in the flower-like carbon materials ( CoMo-MI-T , MI = 2-Methylimidazole, T = 400, 500, 600, 700 °C) has been synthesized by a simple pyrolysis , in which bimetallic CoMo-MI precursors can be conveniently converted from crystalline cobalt-based MOFs of Co-MI by solvothermal reaction. The pyrolyzed CoMo-MI-T series exhibits a hierarchically porous nanostructure, high Co 3 Mo 3 C/N content, suitable N-doping, graphitic carbon layers as well as well-preserved flower-shaped morphology, which shows an excellent OER performance. Among them, the most optimal CoMo-MI-600 owns the small overpotential of 316 mV at 10 mA cm −2 and Tafel slope of 89.9 mV dec −1 in 1.0 M KOH solution. Meanwhile, the rotating ring-disk electrode technique is examined to verify near 4-electron transfer process for CoMo-MI-600 together with a high Faradaic efficiency of 98.7%. The well-performed CoMo-MI-600 electrocatalyst may be stemmed from the best balance of the synergistic effect of abundant multi-component, suitable electrical conductivity and large porosity. The current work will provide a new route to prepare MOF-derived bimetallic active sites in porous carbon nanomaterials with satisfactory activity and robust stability in the relevant energy applications .
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