Design and Optimization of ZnO-Based Photoanodes for Enhanced Photoelectrochemical Water Splitting: Integrating Heterojunction Construction and Dye-Sensitization Approaches with Co-Fe Prussian Blue Analogues as Water Oxidation Catalysts

• Applicant: Dr. Sina Sadigh Akbari
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569714822

Photoelectrochemical (PEC) water splitting is a promising approach for sustainable hydrogen production by utilizing semiconductor photoelectrodes to harvest solar energy. However, the four-electron oxidation of water remains a critical bottleneck due to its sluggish kinetics and harsh chemical conditions. Given the high abundance, cost-effectiveness, and well-aligned band positions, ZnO has emerged as a promising photoanode for PEC water oxidation. Nevertheless, the wide band gap of ZnO (~3.3 eV) confines light absorption to the UV region, and its low charge separation efficiency remarkably restricts photocatalytic activity. This project aims to boost the PEC performance of ZnO photoanodes through surface modification with photosensitizers (PSs) and heterojunction construction, while incorporating Co-Fe Prussian blue analogous (CoFe-PBAs) as robust water oxidation catalysts (WOC) to accelerate reaction kinetics. In the first phase of this study, pyridyl-functionalized PS (e.g., methylene blue, perylene diimide-based dye, and a ruthenium-based PS) will be covalently linked to the CoFe-PBA to form PS-PBA hybrid assemblies, which will be coated onto ZnO surfaces to develop dye-sensitized photoanodes. The direct electronic communication between the catalytic center (cobalt sites in PBA) and PS via [Fe(CN)5] will enhance charge transfer and separation efficiency, improving photocatalytic activity. Furthermore, the integration of chromophores extends the photoanode’s light absorption into the visible spectrum, addressing the intrinsic limitation of ZnO. In the second phase, the ZnO photoanode will be deposited with secondary oxide semiconductors (such as TiO2, NiO, and BiVO4) to form heterostructures to facilitate photogenerated charge separation. The incorporation of CoFe-PBA with these heterojunctions is expected to enhance not only the PEC performance but also the robustness of proposed photoanodes under operational conditions. Advanced characterization techniques (e.g., FT−IR, Raman, XPS, UV-Vis, and PL spectroscopies, as well as XRD, SEM, and TEM) will explore the structural, electronic, and morphological properties of photoelectrodes, while XAS will provide more insights into chemical environment of elements. Finally, PEC oxygen evolution will be studied via cyclic voltammetry, linear sweep voltammetry, and chronoamperometry under dark and light conditions to determine critical parameters, including photocurrent density, Faradaic efficiency, electrochemically active surface area (ECSA), and internal photon-to-current conversion efficiencies (IPCE). Electrochemical impedance spectroscopy (EIS) and spectro-electrochemical methods will further elucidate charge transfer mechanisms and interfacial processes in water oxidation. Overall, this research seeks to develop a new generation of ZnO-based photoanodes coupling PBA as a highly active WOC to provide efficient and stable PEC water oxidation.

• DFG Programme: Research Grants