Direct Z-Scheme Heterostructure of In Situ Planted ZnO Nanorods on g-C<sub>3</sub>N<sub>4</sub> Thin Sheets Sprayed on TiO<sub>2</sub> Layer: A Strategy for Ternary-Photoanode Engineering toward Enhanced Photoelectrochemical Water Splitting
Ahmed Esmail A. Aboubakr, Mahmoud Kamal Hussien, Amr Sabbah, Ahmed E. Hassan, Mohamed Hammad Elsayed, Zhenhai Wen, Kuei‐Hsien Chen, Chen‐Hsiung Hung
Abstract
In this study, we developed an approach to enhance the separation and transfer of charge carriers for photoelectrochemical water splitting in solar-driven hydrogen production. We achieved this by designing a highly efficient Z-scheme TiO 2 /g-C 3 N 4 /ZnO photoanode. The process involved electrodepositing a thin TiO 2 layer on FTO and optimizing the in situ ZnO implantation onto g-C 3 N 4 . These composites were confirmed by XRD, SEM, EDX, and TEM measurements. The growth of ZnO on g-C 3 N 4 resulted in strong chemical adhesion between the interface of ZnO and g-C 3 N 4, as supported by XPS data, and increased active surface area, as demonstrated by BET. The composition of ZnO and g-C 3 N 4 facilitated rapid charge separation and retarded change recombination through directional charge migration and decreased charge resistance, as evidenced by PEIS and TRPL measurements. Our airbrushing procedure for fabricating the g-C 3 N 4 /ZnO composite on TiO 2 also enhanced the charge collection efficiency, enabling us to construct a high-performance photoanode. The Z-scheme-type charge migration route was verified by EPR spectroscopy by trapping the radicals generated by charges and holes. PEC-WS measurements showed that TiO 2 /g-C 3 N 4 /ZnO heterostructure improved the produced photocurrent by about 160-, 40-, 20-, 8-, 2-, and 2-fold, relative to pristine g-C 3 N 4, pristine ZnO nanorods, ZnO/g-C 3 N 4 composite, pristine TiO 2, TiO 2 /ZnO, and TiO 2 /g-C 3 N 4, respectively, versus reversible hydrogen electrode (RHE) at 1.23 V. The charge carriers’ separation and injection measurements showed that the fabrication of this ternary photoanode remarkably improved the PEC-WS performance. DFT results contributed to a deeper understanding of the mechanism of the photocatalytic process and confirmed that the as-fabricated ternary heterojunction promoted the separation/transfer efficiency of the photogenerated charge carriers, thereby promoting the activity of the photocatalytic process. This work could pave the way for better fabrication of ternary-based photoanodes.