Constructing carbon-cohered high-index (222) faceted tantalum carbide nanocrystals as a robust hydrogen evolution catalyst-Shichun Mu's group

The electrocatalysis of nanoscale group V metal carbides (e.g. TaC) has almost received far less attentions owing to lack of active sites. Our theoretical calculations show that high-index (222) facets of TaC are dramatically more active than its other facets towards hydrogen evolution reaction (HER). However, the easy evolution of exposed high-index (222) facets causes a big challenge in fabrication. Here, to obtain the carbon-cohered high-index (222) faceted tantalum carbide nanocrystals (TaC NCs@C), we first develop a novel chlorine-assisted “micro-cutting-fragmentation” technique by incomplete chlorination towards bulk TaC. Interestingly, benefiting from transition zones between in situ formed carbon layers and (222) facets, the evolution of high-index (222) facets with high surface energy can be prevented during the preparation and electrochemical reaction. When evaluated as a HER catalyst, TaC NCs@C presents a low overpotential of ~146 mV at 10 mA cm^-2, a large exchange current density of 9.69×10^-2 mA cm^-2 and outstanding long-term cycling performance. To the best of our knowledge, this HER performance is far preferable to that of the reported group V metal carbides-based catalysts. In the light of the highly generic nature, the methodology developed in this study can be widely applied to produce other in situ carbon armored high-index faceted metal carbide nanocrystals.