Expediting Hydrogen Evolution through Topological Surface States on Bi₂Te₃

Recently, the development of efficient and non-noble metal electrocatalysts with good 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 Bi 2 Te 3 with different thicknesses using the molecular beam epitaxy method, and found that these thin films exhibit high electrocatalytic activity in HER. The 48 nm Bi 2 Te 3 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 Bi 2 Te 3 is not a good electrocatalyst, the Bi 2 Te 3 thin films with partially oxidized surfaces or Te vacancies have high HER activity. The existence of the corresponding surface oxides on the Bi 2 Te 3 thin films is supported by our X-ray photoelectron spectroscopy data. We have also made a direct comparison between a Bi 2 Te 3 and a Bi 2 Te 3:Fe thin film on their magneto-transport properties and HER performances. Particularly, this work demonstrates that the topological surface states play a key role in enhancing the HER performance. Our study offers a direction to design cost-effective electrocatalysts.