Monodispersed metal (Cu, Pd, Pt, Rh) nanoparticles have been anchored on reduced graphene oxide (rGO) by a facile electrochemical co-deposition method. Scanning electron microscopic images reveal the presence of homogeneously dispersed metal nanoparticles on the rGO nanosheets. The as-prepared nanocomposites demonstrate excellent electrocatalytic activity for electroreduction of NO3- and NO2-. The mechanisms associated with the best performed Rh-rGO were studied in detail by cyclic voltammetry, X-ray photoelectron spectroscopic (XPS) and Fourier transformed ac voltammetry. It is proposed that the electrocatalytic reduction of NO3- on Rh-rGO is catalyzed by an adsorbed H* (H-aq(+) + e(-) -> H*) species to form NO2- which is further catalyzed by H* to form a surface confined NO* intermediate. Rh-rGO displays high electrochemical stability for NO3- reduction over the pH range of 4-9, which could be a suitable candidate for applications in remediation of NO3- contamination. (c) 2018 Elsevier Ltd. All rights reserved.