  Surface states refer to electronic states emerging as a solid material
terminates at a surface, and can be present in many systems. Despite their
spatial proximity to material surfaces, surface states have been largely
overlooked in fundamental understanding of surface catalysis and potential
real-world applications, because of their vulnerability to local impurities or
defects. In contrast, the recently discovered three-dimensional topological
insulators (3DTI) have exceptionally robust metallic surface states that are
topologically protected against surface contamination and imperfection. The
robust topological surface state(s) (TSS) provides a perfect platform for
exploiting novel physical phenomena and potential applications of surface
states in less stringent environments. Here we employ first-principles density
functional theory to demonstrate that the TSS can play a vital and elegant role
in facilitating surface reactions by serving as an effective electron bath. We
use CO oxidation on gold-covered Bi2Se3 as a prototype example, and first show
that the TSS is preserved when a stable ultrathin Au film is deposited onto a
Bi-terminated Bi2Se3 substrate. Furthermore, the TSS can significantly enhance
the adsorption energy of both CO and O2 molecules, by promoting different
directions of electron transfer. For CO, the TSS accepts electrons from the
CO-Au system, thereby decreasing the undesirable occupation of the CO
antibonding states. For O2, the TSS donates the needed electrons to promote the
molecule towards dissociative adsorption. The present study adds a new arena to
the technological potentials of 3DTI, and the central concept of TSS as an
electron bath as revealed here may lead to new design principles beyond the
conventional d-band theory of heterogeneous catalysis.
