The catalytic activity of Au and Au-Pd core-shell nanoparticles is investigated at the liquid-liquid interface. The particles are shown to catalyse a process which is attributed to interfacial oxygen reduction. The Au-Pd particles are shown to be more active and correlations made between the catalytic activity and particle radius, surface area and concentration give insight into the mechanism of the catalytic process. Comparison is also made with an analogous bipolar configuration, formed by making contact between the liquid half-cells using a gold wire. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.