Direct Z-Scheme Heterostructure of In Situ Planted ZnO Nanorods on g-C₃N₄ Thin Sheets Sprayed on TiO₂ Layer: A Strategy for Ternary-Photoanode Engineering toward Enhanced Photoelectrochemical Water Splitting

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.

Sensitization of TiO2/g-C3N4 Heterostructures via Pd–Au Cocatalysts: A Rational Design of Water Splitting System for Green Fuel Production

“…The primary goal of this approach to engineering heterojunctions is to overcome the limitations of individual semiconductors by leveraging electronic and chemical interfaces to enhance intimate contact for maximum charge separation and light harvesting . Recently, various innovative multiple-component heterojunctions have been reported in different studies, i.e., CuS/TiO 2 (P–N heterojunction), Pd–Rb 2 O@g-C 3 N 4 /TiO 2 (type II heterojunction), Cu-doped@ZnIn 2 S 4 /TiO 2 (Z-scheme heterojunction), TiO 2 /g-C 3 N 4 /ZnO (Z-scheme heterojunction), Pd-SrO@TiO 2 /gCN (type II heterojunction), Ni@TiO 2 @g-C 3 N 4 (Z-scheme heterojunction), NH 4 TiOF 3 TiO 2 /g-C 3 N 4 (Z-scheme heterojunction-3D camellia), and others, for photocatalytic H 2 production. The proper coupling of materials (favorable heterojunction) by an appropriate synthetic technique could ultimately harvest an efficient rate of H 2 evolution .…”

Trace Au Induced Growth of Mixed-Phase MoS2 Nanosheets on 2D g-C3N4 to Facilitate the Well-Organized Charge Migration in Photocatalytic H2 Evolution

“…As a widely studied metal-free photocatalyst in hydrogen evolution, graphite phase carbon nitride (g-C 3 N 4 ) has many outstanding merits, such as the appropriate band gap (2.78 eV), visible light responsibility, proper energy band position for hydrogen evolution, and rich coordination sites. In addition, the flexible two-dimensional (2D) structure and modifiable surface make g-C 3 N 4 an ideal platform for the construction of heterostructures. − However, the photocatalytic performance of g-C 3 N 4 is unsatisfactory, owing to the serious charge recombination and the lack of surface active sites. , Many efforts, such as doping, metal decoration, construction of heterostructure, and morphology and structure engineering, have been made to improve the photocatalytic performance of g-C 3 N 4 . Among them, combining 2D g-C 3 N 4 with 2D MoS 2 is an attractive strategy due to their similar 2D layered structures, which can provide a large specific area and guarantee sufficient contact between active sites and water.…”

Origin of the Improved Photoelectrochemical and Photocatalytic Activity in a ZnO-TiO2 Nanohybrid Revealed by Experimental and Density Functional Theory Studies

“…Thus, the formation of an optimal heterojunction is very important and depends mainly on the relative band edge position of the semiconductors and uniform interaction across the interface . The combination of zinc oxide (ZnO) and titanium dioxide (TiO 2 ) is suitable for the formation of a type II heterojunction through surface-to-surface contacts between the semiconductors. , Moreover, both semiconductors have shown great promise as photocatalysts and photoelectrodes due to their wide bandgap (∼3.2 eV) and high activity. − In addition, the high exciton binding energy of ZnO (60 meV) makes it an ideal counterpart for TiO 2 , which facilitates exciton dissociation . The type II heterojunction between ZnO and TiO 2 hinders quick recombination of photogenerated charge carriers in photocatalytic and photoelectrochemical applications. , …”