We examined the origins of the high HER activity of Pt17/CB. Recent studies have suggested that miniaturization creates surface Pt atoms with diverse electronic states, and that high activity occurs when these electronic states are favourable for the progression of reactions. In our previous study, DFT calculations revealed that in the optimized structure of Pt17/graphite (Fig. ), Pt atoms with various charges and local DOSs are mixed (Fig. ). Specifically, it was revealed that 1) two Pt atoms (I = 6 and 12) contact the graphite, 2) Pt atoms on terraces (I = 1, 4, 7, and 17) are positively charged, and 3) Pt atoms at steps and corners (I = 2, 3, 5, 8-11, and 13-16) are