Two-dimensional ZnO nanowalls for gas sensor and photoelectrochemical applications

Zinc oxide (ZnO) nanowalls were vertically grown on a glass substrate through a fast, low-temperature, catalyst-free process in a tube furnace. The morphology and microstructure of ZnO nanowalls were characterized by field-emission scanning electron microscopy, x-ray diffraction analysis, transmission electron microscopy, and photoluminescence measurements. The ZnO nanowall films showed strong UV emission and preferential c-axis orientation, with a hexagonal structure. Potential applications of the ZnO nanowalls were further investigated through experiments. The sensitivity of ZnO-based carbon monoxide gas sensors increased with increasing temperature and reached a maximum value at 300°C. In photoelectrochemical experiments, direct photoelectrolysis of water to generate hydrogen was performed using the ZnO nanowalls as the working photoelectrode. For an external bias of 1.2 V, the photocurrent densities reached 0.037 A/cm² under Xe lamp illumination.