Influence of the morphology of ZnO nanowire arrays on the photoelectrochemical water splitting efficiency

Spyros Yannopoulos, ICE/HT, FORTH, Rio-Patras, GREECE
Stelios Neophytides, Ice/ht, Forth, Rio-patras, Greece



The low-cost supply of electricity using renewable energy sources, particularly solar, is today one of the pervasive challenges worldwide aimed at alleviating the quick depletion of natural resources and mitigating carbon dioxide emissions. Among the renewable power sources, photocatalytic and photoelectrochemical (PEC) water splitting offers a promising way for hydrogen production by solar energy. Since the possibility of large-scale use of hydrogen in the future as a transport fuel increases the potential for the above-mentioned renewable energy technology, a large number of investigations is currently underway to develop PEC cells with high stability and efficiency. Apart from TiO2 which stands as the most thoroughly explored material, ZnO has also been scrutinized as alternative solution to TiO2. The role of the ZnO nanowire (NW) morphology on hydrogen production is an open issue to be resolved and is the subject of the current work.
ZnO NWs were grown by the chemical bath deposition method on FTO (SnO2:F) conductive glass substrates. Samples with different diameters ranging from 40 nm to 250 nm (with narrow size distribution) were prepared by properly tuning the NW’s growth parameters, and were employed as anodes of a PEC cell. A hydrogen reference electrode and a platinum wire as cathode were used. Cyclic voltammetry was used for evaluating the stability and the efficiency of the anode electrode for hydrogen production. The I-V curves of NW arrays exhibit a non-monotonic behavior in relation to the NW diameter, where the photocurrent increased with increasing diameter until an optimum value. Time resolved cyclic voltammetry experiments of the ZnO NW anodes confirmed their good stability. The high photocurrent, low open circuit potential and good stability suggest that ZnO NW arrays constitute a promising platform for PEC solar hydrogen production.