【International Papers】Photocatalytic optimization of ZnO–Ga₂O₃ composite thin films for PEC water splitting: effects of thickness, environment, and annealing temperature

      Researchers from the Nazarbayev University have published a dissertation titled " Photocatalytic optimization of ZnO–Ga₂O₃ composite thin films for PEC water splitting: effects of thickness, environment, and annealing temperature " in RSC Advances.

Background

      Modern electrode materials for PEC applications include graphene-based compounds, MXenes, polymers, metal oxides and their multilayered composites. Among these, metal oxides have exhibited superior performance, with ZnO emerging as a particularly promising candidate due to its wide band gap (3.37 eV), non-toxic nature, and cost-effectiveness, making it one of the potential candidates for photocatalysis. The introduction of dopants such as Ga, Cu, In, and Al into ZnO has been shown to enhance its electrical and optical properties, thereby improving PEC cell efficiency.

Abstract

      This study reports a systematic investigation into the photoelectrochemical (PEC) performance of Ga₂O₃/ZnO (GZO) composite thin films fabricated via RF magnetron sputtering. GZO films were deposited on FTO/Glass and titanium (Ti) foil substrates, with key fabrication parameters – namely deposition time, annealing gas atmosphere, and annealing temperature – systematically varied to optimize photocatalytic activity. Surface morphology and crystallinity were evaluated using SEM and XRD, respectively, revealing that both deposition time and annealing conditions significantly influence grain structure and crystallinity, which in turn affect PEC performance. Among the tested conditions, films deposited for 25 minutes and annealed in air exhibited optimal performance, with annealing at 600 °C on Ti foil substrates yielding the highest photocurrent density of 1.7 × 10⁻⁴ A cm⁻² at 1.23 V vs. RHE. Electrochemical impedance spectroscopy (EIS) confirmed improved charge transfer properties at this temperature, although stability testing indicated potential trade-offs between performance and long-term durability. These findings highlight the critical role of thermal and atmospheric control during post-deposition treatment in tailoring the structural and electronic properties of GZO thin films. The optimized GZO photoanodes demonstrate strong potential for low-cost, efficient, and scalable solar hydrogen production, contributing to the advancement of sustainable energy technologies.

Conclusion

      This work report optimization of GaO-ZnO (GZO) composite thin films for photocatalytic applications on FTO/Glass and Ti foil substrates. The study underscores the importance of annealing conditions including gas environment, thickness and annealing temperature. Comprehensive characterization revealed that as-deposited sample has crystalline nature and annealing enhances crystallinity directly influencing PEC performance. GZO films deposited on Ti foil and annealed at 600 °C achieved the highest photocurrent with improved charge carrier dynamics and light absorption properties.

      This study provides a pathway for developing low-cost, efficient, and scalable materials for green hydrogen production via PEC water splitting. The insights gained lay a foundation for further advancements in sustainable energy technologies, emphasizing the potential of GZO thin films in addressing global energy challenges.