Role of topological surface states and mirror symmetry in topological crystalline insulator SnTe as an efficient electrocatalyst

The surface orientation dependence on the hydrogen evolution reaction (HER) performance of topological crystalline insulator (TCI) SnTe thin films was studied. Their intrinsic electrochemical activities were determined by the linear sweep voltammetry and cyclic voltammetry measurements, in which the obtained electrochemical surface areas agree well with their surface topology as revealed by atomic force microscopy image analysis. It was found that the SnTe (001) and (111) surfaces exhibit superior intrinsic activities over those of various topological quantum and nanostructured materials such as the Pt-group-metal-based chiral crystals, while the (211) surface shows uncompetitive activity. Our density functional theory calculations reveal that while pure (001) and (111) are not good electrocatalysts, the SnTe thin film with Sn vacancies or partially oxidized surfaces, with the latter as evidenced by the X-ray photoelectron spectroscopy analysis, have high HER activity. The theoretical calculations show that the overall performance of the (001) and (111) surfaces with topological surface states (TSSs) is better than that of the (211) surface without TSSs, which is further confirmed by the weak antilocalization effect in magneto-transport measurements. The high electrocatalytic activity of SnTe (001) and (111) can thus be attributed to the enhanced charge transfer between hydrogen atoms and the TSSs. The absence or fragility of TSSs in the lowly symmetric SnTe (211) explains its relatively low HER performance. Our study offers a direction to design cost-effective electrocatalysts by tuning the TSSs and mirror symmetry of TCIs.