Continuous Hydrogen Photogeneration at a Soft Interface Comprising a Subnanoliter Volume Organic Phase

Abstract Solar energy-driven hydrogen evolution reaction (HER) remains an important topic in energy-related research. A biphasic (aqueous–organic) system allows for a relatively simple design with a soft interface as a reaction site. The electron donor from the organic phase acts as both photosensitizer and catalyst, enabling HER from the hydrated protons in the aqueous phase in the presence of light. Here, we demonstrate a biphasic system allowing for continuous hydrogen photogeneration, with the organic phase reduced to a subnanoliter droplet of decamethylruthenocene (DMRc) solution in α,α,α-trifluorotoluene (TFT) placed on a recessed Pt microelectrode. Proton transfer to the TFT phase was ensured by negative chemical polarization of the liquid|liquid interface formed at the orifice of the microelectrode cavity. The whole system was kept in an Ar atmosphere, and the Pt microelectrode potential enabled electrochemical recycling of electron-donor molecules. H2 was detected at the scanning electrochemical microscopy (SECM) tip placed above the droplet only in the presence of light. Photogenerated HER was also observed in H2 atmosphere with protons locally generated at the SECM tip next to the liquid|liquid interface, indicating proton transfer. These results demonstrate that continuous photogenerated HER may be realized with the sustainable system consisting of a minimal volume of organic phase.