Rationally designed zinc oxide nanosphere and multi-walled carbon nanotube composite with enhanced photocatalytic and photoelectrochemical performance

Abstract

Photoelectrochemical (PEC) water splitting represents a promising route toward sustainable solar-to-hydrogen energy conversion. Zinc oxide (ZnO), with its wide bandgap (∼3.37 eV), high electron mobility and optical transparency has been intensively investigated as a photoanode material. However, its practical utilization remains limited by insufficient visible-light absorption and photocorrosion-induced instability. Here, we present a rationally engineered composite photoanode comprising ZnO nanospheres electrostatically integrated with surface-functionalized multi-walled carbon nanotube (MWCNT), forming a highly conductive and robust interfacial network. The ZnO nanospheres, assembled from quantum dots, ensure high surface area and efficient light harvesting, while the MWCNT network facilitates rapid charge transport and suppresses electron-hole recombination, as evidenced by pronounced photoluminescence quenching. This architecture delivers a remarkable photocurrent density of 417 μA/cm2 at 1.23 VRHE, corresponding to a 29.7-fold enhancement compared with pristine ZnO. In addition, the composite achieves a hydrogen yield of 3.44 μmol/cm2 (12.3 times higher) and accelerates pollutant degradation kinetics by 21-fold, demonstrating multifunctional performance. The synergistic interplay between ZnO nanostructures and MWCNTs not only enhances charge transfer dynamics but also imparts superior photostability. These findings highlight a scalable materials design strategy for developing high-efficiency, durable photoanodes, offering broad implications for next-generation solar fuel production and environmental remediation technologies.