To gain insights about the valence state, interatomic distances, and crystal structure of Cr2O3 within the nanocapillaries of rGO, X-ray absorption spectroscopy (XAS) measurements were conducted. Figure shows the first derivatives of X-ray absorption near edge structure (XANES) spectra of Cr2O3/rGO-1.8V-1min and Cr2O3/rGO-1.8V-15min as well as Cr foil, K2Cr2O4 and Cr2O3 bulk materials as references. The positions of K-edge (Minimum of the first derivative, indicated by black arrow in Figure ) of reference Cr2O3, Cr2O3/rGO-1.8V-1min, and Cr2O3/rGO-1.8V-15min are observed at the same energy, indicating that the valence state of Cr in the Cr2O3/rGO is trivalent. The comparison between the Fourier transformed (FT) spectra of the reference Cr2O3 and the Cr2O3/rGO samples give further insight into the crystalline structure of the obtained Cr2O3 (Figure ). The short distant structure (< 3 Å) of the synthesized Cr2O3 resembles the reference closely. However, the low intensity of peaks in the longer range (> 3 Å) suggests that the Cr2O3 inside the Cr2O3/rGO has a different structure compared to bulk Cr2O3. Via fitting the FT spectra, the interatomic distances of the created Cr2O3 can be estimated and compared to the bulk reference. A more detailed explanation about the fitting process in which a variety of possible Cr2O3 structures were fitted to the obtained Cr2O3/rGO spectra, is given in the supplementary information (see Figure -19 and Table. S1-6).