Flexible and free-standing hetero-electrocatalyst of high-valence-cation doped MoS2/MoO2/CNT foam with synergistically enhanced hydrogen evolution reaction catalytic activity

Abstract

Molybdenum dioxide (MoO₂) and molybdenum disulfide (MoS₂) are considered as promising non-precious metal electrocatalysts for the hydrogen evolution reaction (HER). However, the thermodynamic inactivity of MoO₂ and poor conductivity of MoS₂ result in unsatisfactory catalytic activities for individual materials. Here we developed a high-performance HER hetero-electrocatalyst of high-valence-cation doped MoS₂/MoO₂ composites incorporated in carbon nanotube (CNT) foam by a simple one-step synthesis. MoO₂ is stably attached and partially sulfurized into MoS₂ on CNT foam, which couples the features of abundant active sites of MoS₂, good conductivity of MoO₂, flexibility and porosity of the CNT foam matrix, and unique doping effects of high-valence cations to synergistically enhance the HER activity. This delicately designed hetero-electrocatalyst thus exhibits low overpotential (62 mV @ η₁₀), small Tafel slope (44 mV dec⁻¹), and extremely high double-layer capacitance (217.9 mF cm⁻²). The performance remains almost unchanged after hundreds/thousands of times of bending/CV scans, and shows long-term stability at both low and high currents. Experiments and density functional theory calculations suggest that the high-valence-cation doping improves both electrical conductivity and catalytic activity of the materials. This state-of-the-art electrocatalyst can be directly used as an easily processable, flexible, free-standing, and cost-effective electrode without binders in diverse environments.