Extending the polyol reduction process into the second dimension: Oxide thin film reduction

The formation of extended metal thin films (<5 nm) or monolayers on oxide surfaces, for applications in (electro-)catalysis, has never been achieved due to the high interfacial energy of the metal/oxide interface that always results in a 3D growth of the deposited metal. To realize 2D growth, the outermost surface of the oxide must be reduced prior to metal deposition in the same system. Here, we demonstrate that the polyol method, typically used for metal nanoparticles synthesis, can be used for the reduction of oxide thin films. The reduction of the oxide layer upon heating in ethylene glycol was electrochemically monitored in situ by measuring the open circuit potential and confirmed by cyclic voltammetry and near ambient pressure X-ray photoelectron spectroscopy. The reduction of oxide thin films could be verified for nanoparticles of Sn, Ni and Sb-doped SnO₂ in accordance with thermodynamic calculations. This method will enable the formation of metal thin films and monolayers on oxide substrates for applications in (electro-)catalysis.