Thin films of controlled thickness of Co/Al layered double hydroxide with different Co and Al percentages have been electrosynthesized by the cathodic reduction of a 0.03M Co and Al nitrate solution. The electrochemical behaviour of the films deposited on Pt or ITO electrodes has been deeply studied in 0.1M NaOH solution. Our findings demonstrate that as soon as a potential is applied in the anodic direction, the films undergo an irreversible change of phase.