To prepare co-surface treatment samples, after TiO2 coating, the electrodes should be hydroxylated by dropping 10 ml deionized water untill they dried, then dipping the electrodes in a solution of suitable precursor as 0.05 M solution of aluminum isopropoxide in dry ethanol followed by rinsing with ethanol and sintering at 550 C for 30 min, The thickness of the barrier layer was controlled precisely by the deposition cycle 1, 2 and 3 represented as F-T-xA (x = 1, 2, 3).