Fig. 5: Chemical analysis of the Co3O4@C/GPO catalyst after water electrolysis.

a X-ray photoelectron spectra of the Co 2p (left) and O 1s (right) core levels for a 20-Co3O4@C/GPO electrode. b Same spectra for a 20-Co3O4@C/GPO electrode after OER chronopotentiometry at 10 mA cm–2 for 2 h. c Same spectra for a 20-Co3O4@C/GPO electrode after OER chronopotentiometry at 5 mA cm–2 for 24 h. Color assignment for the different areas: Co3+ (blue), Co3+ satellite (pink), Co2+ (green), Co2+ satellite (yellow), OH/H2O (purple), O–Co (brown). Source data are provided as a Source Data file.