ZnO nanorod arrays for photoelectrochemical cells

The splitting of water using photoelectrochemical (PEC) cells to produce hydrogen is one of the most sustainable forms of energy production and more and more 1-D nanostructrues semiconductors used as photoelectrodes have been studied extensively. However, it is not clear whether the photoconversion efficiencies of such nanostructure devices are limited by the architectures of the 1-D electrodes. Here, we explore the effect of the architecture like the length and width of ZnO nanorods on the PEC cells performance for the first time. The as-prepared nanorods have diameters of 40-50 nm and lengths of 400-800 nm. Preliminary measurements exhibit that the resulting electrodes have promising PEC properties. Mott-Schottky measurements give a flat-band potential of +0.10 V, a carrier density of 3.7×10 ¹⁷ cm ^-3, and a space-charge layer of 26 nm. The photocurrent of 800 nm-long nanorods shows 10 times higher than that of 400 nm-long ones, and an encouraging maximum photoconversion efficiency of 0.25% is obtained under illumination of 100 mW/cm ² (AM 1.5), which is among the highest reported for an undoped ZnO photoelectrode to date.