Platinum-based catalysts currently have shown the most efficient electrocatalytic activity for the hydrogen evolution reaction (HER, 2H+ + 2e- → H2 ). However, the high price and scarcity of Pt oblige us to reduce the amount of Pt used in electrocatalytic materials. A promising strategy to reduce the use of Pt is the synthesis of single-atom or pseudo atomic-scale Pt. In this strategy, the size of Pt particles further decreases from nano- to sub- nanometer or atomic scale. Consequently, the catalytic properties of the atomic-scale metal can be also drastically changed, providing the possibility of selective tuning of the catalyst activity. Nevertheless, the atomic-scale catalysts are not stable because of their high surface energy and therefore, they should be decorated on the supports providing strong metal–support interactions to prevent the agglomeration of atoms.