Table 2. Summary of oxidation states for Pt species of different electrocatalysts obtained from XPS analysis.

Sample	Pt species on surface	Binding energy of Pt4f7/2(eV)	Relative intensity (%)
Pt/VC	Pt(0)	71.9	33.36
	Pt(II)	72.9	18.31
	Pt(IV)	74.6	48.33
Pt/rGO	Pt(0)	71.9	31.62
	Pt(II)	72.7	28.06
	Pt(IV)	73.5	40.32
Pt/S-rGO	Pt(0)	71.7	38.45
	Pt(II)	72.6	27.16
	Pt(IV)	74.3	34.39