Nickel Doping Enhances the Reactivity of Fe3O4(001) to Water

We studied how nickel doping affects water adsorption at the Fe3O4(001) surface to understand the enhanced performance of spinet ferrites for the water-gas shift and oxygen evolution reactions. Two different configurations were prepared: 2-fold-coordinated Ni adatoms on top of the surface and Ni atoms incorporated into the octahedral sites of the support. Using temperature-programmed desorption, X-ray photoemission spectroscopy, and scanning tunneling microscopy, we show that water is adsorbed and dissociated on the nickel adatoms at room temperature, resulting in Ni-OH species and surface hydroxyl groups. Nickel atoms incorporated into the support do not directly adsorb water but modify the electronic properties of the surface Fe, and water adsorbed on these sites has similar characteristics as that of water adsorbed on intrinsic surface defects. In both cases, the presence of Ni significantly alters the growth of the first water monolayer on Fe3O4(001).