  Recently, the development of efficient and non-noble metal electrocatalysts
with excellent durability for the hydrogen evolution reaction (HER) has
attracted increasing attention. The exotic and robust metallic surface states
of topological insulators (TIs) are theoretically predicted to enhance surface
catalytic activity of overlaying catalysts, but no experimental evidence for
TIs directly used as electrocatalysts has ever been reported. In this work, we
fabricated the TI thin films of Bi2Te3 with different thicknesses using the
molecular beam epitaxy method, and found that these thin films exhibit high
electrocatalytic activity in HER. The 48 nm Bi2Te3 thin film has the best
performance, which is attributed to its largest active area arising from the
spiral growth mode of triangular domains as revealed by atomic force microscopy
imaging. Importantly, our theoretical calculations reveal that while pure
Bi2Te3 is not a good electrocatalyst, the Bi2Te3 thin films with partially
oxidized surfaces or Te vacancies have high HER activity. The existence of the
corresponding surface oxides on the Bi2Te3 thin films is supported by our X-ray
photoelectron spectroscopy data. Particularly, we demonstrate that the
topological surface states play a key role in enhancing the HER performance.
Our study offers a new direction to design cost-effective electrocatalysts.
