The invention relates to a method of preparing a metal oxide/metal composite, comprising depositing a metal oxide from a dispersion in a liquid on a metal surface; or depositing a metal oxide in the presence of a metal from a dispersion in a liquid on a substrate; or depositing a metal oxide from a metal salt solution on a metal substrate. The metal oxide/metal composites obtained by the process show synergistic antimicrobial activity due to release of high concentrations of redox active species (ROS) at the metal oxide/metal heterojunction. The invention also relates to use of the metal oxide/metal composite as an antimicrobial coating.