In situ electrochemically synthesized Pt-MoO3−x nanostructure catalysts for efficient hydrogen evolution reaction

•In situ electrochemical process to synthesize Pt-MoO3−x nanoflakes (NFs) overgrown on MoS2 surface is reported.•The Pt-MoO3−x NFs showed excellent electrocatalytic hydrogen evolution reaction (HER) performance.•The outstanding HER characteristics are related to existence and increase of Pt-MoO3 interfacial sites and Mo5+ sites.