During the fellowship period, the research activities were centered around the development of light-driven catalytic systems for sustainable hydrogen production and green chemical synthesis. The project addressed the mechanistic understanding and technological challenges of photocatalytic C-H activation and dehydrogenation reactions under mild conditions. The work was structured into three interconnected research themes:
1. Clarifying the Proton Source in Photocatalytic Hydrogen Evolution
Photocatalytic hydrogen evolution is commonly reported using sacrificial organic donors (e.g. alcohols, amines), but the origin of the proton in the generated H2 is often unclear. This project established a protocol to distinguish between real water splitting and sacrificial donor dehydrogenation by employing deuterium labelling strategies using tetrahydrofuran (THF) as the sacrificial donor.
Approach & Methodology: A TiO2-based photocatalyst was tested using THF as the sacrificial reagent. Due to THF’s low acidity and absence of rapid H/D exchange, it allowed precise tracing of proton sources in the reaction via isotope labelling experiments.
Key Findings:
(a) Under low-water conditions, both water and THF contributed protons for H2 evolution.
(b) Water acted as a proton shuttle while THF served as both electron and proton donor.
The findings clarified misconceptions in many reported water-splitting systems and established criteria for evaluating true photocatalytic water splitting.
Publication: Angew. Chem. Int. Ed. 2024, 63, e202408626.
2. Photocatalytic Upgrading of MTBE into Ethylene Glycol Coupled with Hydrogen Production
This task focused on developing a sustainable route to ethylene glycol (EG), an essential commodity chemical, by photocatalytically transforming methyl tert-butyl ether (MTBE), which can be regarded as hydroxyl group protected methanol, to produce ethylene glycol by two consecutive steps.
Catalyst Development: A novel Pt/TiO2 catalyst with co-existing anatase and rutile phases was synthesized to enhance hot electron/hole separation.
Performance: Achieved a high turnover frequency (>2700 h⁻¹) and 67% selectivity toward EG under UV–visible light (320–500 nm) at ambient conditions.
Process Intensification: A major milestone was the transition from batch-scale reactions to a continuous circulation reactor, demonstrating feasibility beyond the lab scale. The reactor operated continuously for 130 hours, yielding 13 g of EG dimer and 1.9 L of hydrogen, with a sustained MTBE conversion of 58%. The hydrolysis of the dimer product afforded ethylene glycol in >99% yield, validating the downstream conversion step.
Mechanism: Radical intermediates were identified via EPR and TEMPO trapping experiments, confirming a radical-based pathway.
Outcome: Demonstrated practical scalability and potential industrial relevance for green EG production from an environmental contaminant.
Publications: Nature Communications 2025, 16 (1), 1-11
3. Light-Driven Hydrogen Release from Formic Acid and Integration with Enzymatic Hydrogenation
In addition to valorising oxidation products, the project also explored an alternative route for sustainable hydrogen production via liquid organic hydrogen carriers (LOHCs). Among LOHCs, formic acid is particularly attractive due to its high hydrogen content. This segment of the project focused on evaluating photocatalytic decomposition of formic acid under mild conditions to enable on-demand H2 generation, with the goal of coupling this hydrogen release to downstream enzymatic hydrogenation reactions.
Catalyst Development and performance: A Pt@TiO2 catalyst was synthesized. Under optimized conditions, the system exhibited high activity for photocatalytic FA dehydrogenation. On-off light experiments confirmed the strict light-driven hydrogen evolution, with minimal thermal contribution, highlighting the potential for light-controlled H2 release from FA.
Outcome: This work demonstrated the integration of LOHC photodecomposition with enzymatic catalysis and established a novel hybrid platform for light-driven hydrogenation at mild conditions, expanding the technological reach of solar hydrogen.
