Cyclic voltammetry (CV) profiling with a scan range of 0 V-2.3 V and scan rate of 5 mV/s. The X-ray photoelectron spectroscopy (XPS, Thermo Scientific, UK, ESCALAB250Xi) depth profile analysis (Ar-sputtering). It applied 100 eV for survey scans and C1s = 284.5 eV for graphite as reference. Time-of-flight secondary ion mass spectrometry (ToF-SIMS, TOF.SIMS 5 IONTOF Munster Germany) depth profile which applied Bi + 30 keV in positive polarity for analysis and a sputter of O 2+ at 1 keV. The sputtering time was 1500 s. X-ray diffraction (XRD, Empyrean I, 1.54 Å) is used to study the GO and Cr2O3/rGO interlayer space. The dry sample were recorded after drying 24 hours in air. Wet GO films were recorded after soaking in DI water for 60 mins. The interlayer space is calculated according to Bragg's law. X-ray absorption fine structure (XAFS) spectra for the Cr K-edge were recorded at BL01B1 of SPring-8. Transmission (standard materials) and fluorescence yield (samples) spectra were acquired using a double-crystal Si(111) monochromator, ion chambers, and a 19-element germanium solid-state detector (SSD) equipped.