Self-supporting composited electrocatalysts of ultrafine Mo2C on 3D-hierarchical porous carbon monoliths for efficient hydrogen evolution†
Molybdenum carbides (MoxC) are regarded as low-cost non-noble metal electrocatalysts for the hydrogen evolution reaction (HER). However, most reported powdery MoxC materials suffer from several drawbacks of polymer binders (such as Nafion) including partial blocking of active sites and decreased long-term stability. The recently developed binder-free MoxC materials are based on pre-treated commercial current-collecting substrates such as carbon cloth and carbon fibers, which make it basically impossible to design hierarchical porosity and achieve uniform distribution of active sites. Herein, we successfully synthesized self-supporting binder-free Mo2C composited electrocatalytic materials by integrating Mo2C nanoparticles with three-dimensional (3D) hierarchical porous carbon monoliths (PCMs) via a facile impregnation followed by in situ carbonization treatment (denoted as 3D Mo2C/PCM). As a result, Mo2C nanoparticles of ∼5 nm were uniformly distributed on the in situ transformed carbon matrix, and their uniform macropores (∼9 μm) and open ordered mesopores (5.6 nm) guaranteed fast mass transport and full exposure of active sites. The optimal 3D Mo2C/PCM sample displayed overpotentials of 81 and 47 mV at 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively, and the corresponding Tafel slopes were 63 and 45 mV dec−1. Benefiting from the outstanding mechanical strength and the easy-to-adjust macromorphology, 3D Mo2C/PCM could be directly used as a self-supporting working electrode without adding any binders. The synthesis strategy in this work may be extended to fabricate other bulky self-supporting carbon-based catalysts.