Electrocatalytic hydrogen evolution reaction (HER) at highly dispersed Pt atoms on nanoporous surfaces is of significance both in practice and in theory. In this work, in situ surface dispersion of tiny amount of Pt (NPGF-t-Pt) on a nanoporous gold film for HER has been carried out by repeated cyclic voltammetry for the first time. It involves simultaneous redox and alloying of Au and Pt atoms at the surface during the cyclic voltammetry. At a critical Pt content of similar to 5 at% that is in situ optimized, the NPGF-t-Pt electrode has nearly the same HER geometrical current density as the nanoporous Pt surface with almost the same surface roughness. The Pt-mass HER current density on the ex situ alloyed nano-Au95Pt5 electrode is about 20 times that on the nano-Pt electrode. A modified HER mechanism containing seven surface elementary reaction steps has been proposed based on the experimental results, which is also supported by density functional theoretical calculation. It gives a deeper insight into the HER at the dispersed Pt atoms (similar to 5 at%) on the NPGF surface. We expect that this work will promote the electrocatalytic HER at dispersed active atoms with a critical content. (C) 2018 Elsevier Inc. All rights reserved.