Formic acid adsorption and decomposition on non-stoichiometric TiO2(110)

We have investigated the adsorption and decomposition of formic acid on the non-stoichiometric TiO2(110) surface using sequential scanning tunneling microscopy (STM) imaging at variable temperature. Formic acid adsorption on the surface displaying the cross-linked (1×2) reconstruction shows no ordered structures upon adsorption at room temperature. The added rows of the reconstructed surface appear disrupted or obscured. Upon ramping the temperature to 673 K the (1×2) reconstruction becomes visible and small islands of (1×1) termination grow within the (1×2) terraces. This behaviour is reminiscent of the (1×2) surface reacting with O2 at elevated temperature. We attribute the formation of the (1×1) islands to the decomposition of the formate and insertion of an oxygen atom into the lattice as the surface re-oxidises. The growth of the surface implies interstitial Ti ions, diffusing out from the bulk, react with either an intact formate molecule or its decomposition product to form the new TiO2 surface.