Pt/PtO2 nanoparticles (NPs) have been prepared by a simple synthetic strategy, easily able to control nanoparticles (NPs) size, consisting in the thermolysis of a suitable precursor in organic solvent under a low oxygen enriched atmosphere. An excellent combination of a low tafel slope of 31 mV/dec with a negligible overpotential was measured for our Pt/PtO2 NPs, due to PtO2 resulting in electron rich Pt island, showing activity higher than that of common Pt. Additionally, the paper proves that it is possible to improve platinum/platinum oxide activity through control of NPs size and reduce platinum loading through its junction and interaction with a further metal oxide. Very high hydrogen production rate of 3.35 mL cm(-2) h(-1) at -0.024 V, obtained by means of an on-line mass spectrometry analysis, to corroborate the results with a realistic hydrogen production estimation, was measured for Pt/PtO2 electrode. Moreover, Pt/PtO2 was stable in corrosive acidic solution during electrolysis under high current density. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.