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

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.