The peaks at 16 nm -1 and 21 nm -1 do not exactly match diffraction peaks of crystalline I2, indicating that solid I2 forms in a crystal structure slightly different from bulk I2, partially in an amorphous state and/or the confined nanocrystals are strongly distorted. The diffraction peak widths (FWHM), as obtained by Gaussian peak fitting (Supplementary Fig. ) are located in the region of 10.5°-19° 2θ. According to Scherrer's equation, this translates into a crystallite size between 0.55-0.9 nm, which fits well to the mean carbon pore size of 0.81 nm and the intensity changes found in SAXS. Qualitatively, the in situ SAXS/WAXS and Raman data analysis provide correlating complementary information. Based on these data, we see that during oxidation, solid iodine particles are deposited in the carbon nanopores. At the same time, significant amounts of I3 -and I5 -are generated. The WAXS correlation peak at 7.5 nm -1 suggests a highly concentrated solution of polyiodides that is, to a large extent, confined to the nanopores. Solid iodine domains are likely to be present in crystalline form, since diffraction peak widths point at crystallite sizes up to 0.9 nm, in accord with the mean carbon pore size of 0.81 nm.