Carbon Quantum Dots and N-Doped g-C3N4 Co-Decorated ZnO Nanorod Arrays for Enhanced Photoelectrochemical Water Oxidation

Zinc oxide (ZnO) is a potential wide band gap semiconductor, but its high photoelectron-hole pairs recombination rate and poor light absorption ability limit its application to photoelectrochemical (PEC) water oxidation. To solve these problems, in this work, a reasonable band structure engineering was carried out on ZnO nanorod arrays (ZnO NRAs) with the co-decoration of nitrogen doped g-C3N4 (NCN) and carbon quantum dot (CQDs) solution. Narrow band gap NCN was loaded onto the surface of ZnO NRAs by a simple spin coating method, and then CQDs were modified on the ZnO/NCN NRAs. The composite photoanode of ZnO/NCN/CQDs NRAs was finally obtained. The PEC performance of the composite photoanode reaches 1.82 times that of the pristine ZnO photoanode, with a photocurrent density of up to 1.20 mA cm-2 at 1.23 V (vs. RHE) bias. The calculated value of ABPE for the composite photoanode was 0.258%, compared with 0.123% for the bare ZnO NRAs. The co-decoration of NCN and CQDs enhanced the charge separation efficiency and expanded the spectral response range, contributing to the improved PEC properties of the composite photoanode.