Photoelectrochemical (PEC) analysis of ZnO/Al photoelectrodes and its photocatalytic activity for hydrogen production

This paper reports the photoelectrochemical (PEC) analysis and the photocatalytic activity for hydrogen production of ZnO/Al photoelectrodes prepared with 0.5, 1 and 5 wt% of Al. The photoelectrodes were obtained by the sol-gel method and used as active material on photocatalyst for hydrogen production under UV-light irradiation. By increasing the aluminium concentration, the band-gap of ZnO decreases, at the same time the photoluminescence intensity decreases too. On the contrary, the PEC test showed an increase in the photocurrent due to the Al presence, which improves the charge transfer because it is a better coupling of the electronic bands of ZnO and Al. The n-type of semiconductor was corroborated by OCP curves, while the electron-hole pair recombination was calculated by electrochemical measurements where Al incorporation diminished the recombination. The electron lifetime calculated from OCP curves increases with Al content, which favours the catalytic activity of ZnO/Al photoelectrodes indicating its efficiency. In concordance, Nyquist plots reveal that ZnO/Al photoelectrodes with highest amount of Al showed low charge transfer resistance. On the other hand, the presence of Al increased the number of active sites as calculated by Turnover frequency (TOF), which is favourable to carry out redox reactions. The photocatalytic activity for hydrogen production was almost 6.6 times higher with respect to ZnO because the presence of Al, which favored the increase of charges and a greater number of active sites. This result is in agree with the information obtained by PEC analysis, where also a higher amount of photocurrent was produced by the Al content in ZnO/Al.