  In order to obtain a comprehensive understanding of both thermodynamics and
kinetics of water dissociation on TiO2, the reactions between liquid water and
perfect and defective rutile TiO2 (110) surfaces were investigated using ab
initio molecular dynamics simulations. The results showed that the free-energy
barrier (~ 4.4 kcal/mol) is too high for a spontaneous dissociation of water on
the perfect rutile (110) surface at a low temperature. The most stable oxygen
vacancy (Vo1) on the rutile (110) surface cannot promote the dissociation of
water, while other unstable oxygen vacancies can significantly enhance the
water dissociation rate. This is opposite to the general understanding that Vo1
defects are active sites for water dissociation. Furthermore, we reveal that
water dissociation is an exothermic reaction, which demonstrates that the
dissociated state of the adsorbed water is thermodynamically favorable for both
perfect and defective rutile (110) surfaces. The dissociation adsorption of
water can also increase the hydrophilicity of TiO2.
