Efficient light-driven charge storage in titania aerogels: From photochemical batch studies to capillary flow reactors

Abstract

A major challenge in photocatalyst design is separating light-harvesting from catalytic steps, for which photo-chargeable materials provide a promising approach for decoupling light-driven energy storage from subsequent dark reactions. This work systematically investigates the exceptional capability of as-synthesized titania aerogels to store electrons upon irradiation, including sacrificial agents, irradiation time, and incident photon flux. Methanol, owing the highest number of α-H atoms, was the most effective sacrificial agent compared to ethanol and isopropanol, enabling electron storage up to 64.8 μmol e- in 100 mg titania aerogel. Moreover, insights from studies in a semi-batch reactor (Xe-arc lamp) were translated to a flow capillary reactor irradiated with UVA LEDs. A characterization of the radiation field of both reactors allowed for an objective comparison of data obtained in the different experimental setups. Using the same charging conditions in the capillary reactor as in the semi-batch reactor yielded a low charging performance, due to a significant light transmission loss caused by low loading. Photocharging conditions were tailored to account for the short optical path length of the capillary reactor by an increase of the titania aerogel loading and a reduced dispersion volume. This enhanced the photocharging rate in the capillary reactor, eventually exceeding that of the batch system by a factor of two. Doubling the catalyst loading increased photonic efficiency fourfold, demonstrating both the potential and challenges of transferring and scaling light-driven processes from batch to flow, and establishing critical design insights for light-driven charge storage in continuous systems.