Enhanced hydrogen evolution reaction over molybdenum carbide nanoparticles confined inside single-walled carbon nanotubes

Carbon nanotubes (CNTs) have shown as unique nanoreactors to tune the catalytic activity of confined nano-catalysts. Here we report that the catalytic performance of molybdenum carbide nanoparticles (MoCx NPs) for the hydrogen evolution reaction (HER) process can be enhanced by encapsulation within single-walled carbon nanotubes (SWNTs) with a diameter of 1-2 nm. The catalyst with MoCx NPs located on the interior surface of SWNTs (MoCx@SWNTs) exhibits a lower onset over-potential and a smaller Tafel slope than the one with MoCx NPs attached on the exterior surface (MoCx/SWNTs). This is likely attributed to the much smaller particle size and the more reduced states of the confined MoCx NPs, as well as the larger specific surface area of MoCx@SWNTs compared with MoCx/SWNTs. In addition, the electronic structure of the confined MoCx NPs might be modified by the confinement effects of SWNTs, and hence the adsorption free energy of H atoms on the confined MoCx NPs, which could also contribute to their higher performance. These results suggest that the SWNTs can be further explored for constructing novel catalysts with beneficial catalytic performance. (C) 2018 Published by Elsevier B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences