Self-supporting composited electrocatalysts of ultrafine Mo2C on 3D-hierarchical porous carbon monoliths for efficient hydrogen evolution

Abstract

Molybdenum carbides (Mo_xC) are regarded as low-cost non-noble metal electrocatalysts for the hydrogen evolution reaction (HER). However, most reported powdery Mo_xC 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 Mo_xC 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.