Controlling the chemical reactivity of nanostructured electrode materials by surface reactive sites

To better control the chemical reactivity of nanostructured electrode materials, a surface reactive site model is proposed based on thermodynamic theory. Impressively, due to the quantum size effect, the close existence of the photoformed electron and hole pairs in nanocrystalline materials and their efficient contribution to the reaction, resulting in chemical activity much enhanced over that of bulk materials. The ratios of the surface vacancy formation energies of Au, Ag, and Cu (111) nanocrystal planes to the volume vacancy formation energies are all 0.25, much lower than the corresponding bulk values. Remarkably, the chemical reactivity of carbon nanotubes, TiO₂ nanotubes, MgO nanoparticle, and ZnO nanoparticle can be attributed to the number of surface reactive sites. In addition, we have also found that stress and vacancies have similar effects, indicating that mechanical activation can effectively improve chemical reactivity. Our model is applicable to nanocrystalline materials of different shapes, dimensions, and crystal structures. (paper)