The in situ and ex situ data allow deriving a detailed reaction mechanism of the (poly)iodide/iodine redox chemistry in nanopore confinement (Fig. ). Specifically, (i) in situ Raman, ex situ UV-vis and in situ SAXS (Fig. ) confirm the formation of I2, I3 -and I5 -during I -oxidation. (ii), I5 -generation is delayed with respect to I3 -upon oxidation process as seen in their Raman intensities (Fig. ). This indicates that larger amounts of generated I3 -and I2 accelerate I5 -formation. (iii), In situ SAXS/WAXS data confirm the formation of solid I2 nanoparticles or clusters in the nanopores.