Carbon Nanotubes Encapsulated Transition Metals for Efficient Hydrogen Evolution Reaction: Coupling Effect of 3d Orbital and π-Bond

Abstract

Abstract Carbon materials are widely used in various industrial applications due to their outstanding stability and robustness in diverse structures, yet it remains a revolutionary and challenging task in activating carbon materials for efficient and low-cost catalysis. Herein, inspired by the successful experimental studies, we for the first-time exploited carbon nanotubes encapsulated transition metal atoms (TM@CNT) for hydrogen evolution reaction (HER) using density functional theory (DFT) calculations. The Gibbs free energy of H-C bond on pristine CNTs is too positive, which prevents the adsorption of H atoms. However, TM@CNT (TM = Fe, Co, Ni) has superior HER performance than that of the widely recognized Pt and MoS2 catalysts, benefiting from disruption of the π conjunctions and activation of the stable sp2 hybridizations between carbon atoms in CNTs. A set of metal-free catalytic surfaces with high HER activity have been developed. Meanwhile, the HER performance of graphene nanosheets loaded on the most ubiquitous facet (111) of transition metals (TM@G, TM = Fe, Co, Ni) also be calculated. However, TM@G shows lower HER activity than that of the TM@CNT, which is attributed to the large curvature of CNTs. These new findings manifest a universal strategy for carbon materials activation that will inspire the rational design of carbon-based electrocatalysts for efficient water splitting.