Dissociative adsorption of formic acid and diffusion of formate on the TiO2(110) surface: the role of hydrogen

Formic acid (HCOOH) dissociates on the rutile TiO2(110) surface into formate (HCOO) and H. Certain ordered structures for HCOO have been observed for different coverages. In the present work, the role of hydrogen in the stability of these structures and also in the process of HCOO diffusion has been studied by means of ab initio density functional calculations. Our calculations show that coadsorption of H is necessary to stabilize the high-coverage p(2×1) geometry. They furthermore explain the observed high mobility of HCOO in a p(2×1)-like environment which is caused by a rather complex movement of HCOO together with H. This process cannot operate at lower coverages and for isolated molecules, which therefore makes HCOO immobile, as suggested by experiment.