Defect-rich ZnO nanorod arrays for efficient solar water splitting

A novel ultra rapid synthetic method for the production of vertically aligned ZnO nanorod (NR) arrays has been demonstrated, using a microwave assisted chemical bath deposition method. High quality NR arrays with controllable film thickness were achieved with fine control of the growth conditions. A fast growth rate averaging 0.9 µm h-1 was achieved in comparison to 0.1 µm h-1 from the conventional chemical bath deposition. The MW synthesised NRs have a high level of n-type doping, which confers excellent photoelectrochemical performance. In comparison with the typical chemical bath deposition synthesised NRs, the ultra-fast MW synthesised NRs offer 3 times more efficient in PEC water splitting. The population densities and electronic states of these defects were monitored using photoluminescence spectroscopy and electrical impedance spectroscopy. The dopant level was further controlled by thermal annealing in air and an optimised density of 1.68 × 1019 cm-3 was achieved after annealing at 500°C. This in turn led to a twofold increase in PEC efficiency to 0.31% with a photocurrent density of 0.705 mA cm-2 at 1.23 V vs RHE, which is one of the best performances from similar ZnO NR structures.