Au surfaces modified by Pd electrodeposits have been found to enhance the rates of nitrate electroreduction in acidic aqueous solutions containing Cd2+ over those of the bare Au substrate in the same media. Rather surprisingly, similar electrocatalytic effects were also observed for ensembles of Au and Pd nanoparticles supported on otherwise inert glassy carbon (GC) surfaces under the same conditions, which suggest that this phenomenon does not originate solely from specific interactions between the two metals. In fact, the overall electrocatalytic activity of GC surfaces decorated with either a fixed number of Au in one case, or a fixed number of Pd nanoparticles in the other, displayed much lower activity than GC surfaces covered with a mixture of half of each of them. This unique behavior may be explained by the ability of Pd to reduce NO2-, which is known to be the main reaction product of NO3- reduction on underpotential deposited Cd on Au. (C) 2019 The Electrochemical Society.