Adsorption of chlorine on ZnO(0001)–Zn and coadsorption with HCOOH

The adsorption of Cl2 on the zinc-terminated ZnO(0001) surface at 300 K was studied with low-energy ion-scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), and work-function and band-bending measurements. The surface saturated with ∼0.30 chlorine adatoms [Cl(a)] per zinc site, sitting above the zinc layer in no apparent registry with the substrate. Combined work-function and band-bending measurements indicate anionic Cl(a). Using formic acid to produce surface formate, the effect of Cl(a) on formate decomposition was studied also. On the chlorine-free ZnO(0001) surface, formate decomposes through two different pathways: dehydration and dehydrogenation. Pre-adsorbed chlorine suppresses the amount of adsorbed formate produced, and enhances the selectivity for its dehydrogenation.