  The band inversion in topological phase matters bring exotic physical
properties such as the emergence of a topologically protected surface states.
They strongly influence the surface electronic structures of the investigated
materials and could serve as a good platform to gain insight into the catalytic
mechanism of surface reactions. Here we synthesized high-quality bulk single
crystals of the topological semimetal Co$_3$Sn$_2$S$_2$. We found that at room
temperature, Co$_3$Sn$_2$S$_2$ naturally hosts the band structure of a
topological semimetal. This guarantees the existence of robust surface states
from the Co atoms. Bulk single crystal of Co$_3$Sn$_2$S$_2$ exposes their
Kagome lattice that constructed by Co atoms and have high electrical
conductivity. They serves as catalytic centers for oxygen evolution process
(OER), making bonding and electron transfer more efficient due to the partially
filled $e_g$ orbital. The bulk single crystal exhibits outstanding OER
catalytic performance, although the surface area is much smaller than that of
Co-based nanostructured catalysts. Our findings emphasize the importance of
tailoring topological non-trivial surface states for the rational design of
high-activity electrocatalysts.
