The chemistry of chromium in the passive film on pure chromium and sputtered AlCr thin films has been studied in situ in an electrochemical cell under potential control using XANES. Depending on the rate of potential increase, the 6-valent chromium can dissolve from the alloy or be trapped in the passive film where it is electroactive i.e. the valence state can be reversibly switched between the 3- and 6-valent states by switching the applied potential. The kinetics of these processes were investigated
