Photo‐recycling the Sacrificial Electron Donor: Towards Sustainable Hydrogen Evolution in a Biphasic System

H2 may be evolved biphasically using a polarised liquid|liquid interface, acting as a “proton pump”, in combination with organic soluble metallocenes as electron donors. Sustainable H2 production requires methodologies to recycle the oxidised donor. Herein, the photo‐recycling of decamethylferrocenium cations (DcMFc+) using aqueous core‐shell semiconductor CdSe@CdS nanoparticles is presented. Negative polarisation of the liquid|liquid interface is required to extract DcMFc+ to the aqueous phase. This facilitates the efficient capture of electrons by DcMFc+ on the surface of the photo‐excited CdSe@CdS nanoparticles, with hydrophobic DcMFc subsequently partitioning back to the organic phase and resetting the system. TiO2 (P25) and CdSe semiconductor nanoparticles failed to recycle DcMFc+ due to their lower conduction band energy levels. During photo‐recycling, CdS (on CdSe) may be self‐oxidised and photo‐corrode, instead of water acting as the hole scavenger. Closing the loop: Consuming a sacrificial electron donor to generate H2 as a solar fuel is not a sustainable clean energy strategy. The oxidised donor must be regenerated in a renewable manner. A novel approach is outlined to close the loop and photo‐regenerate the sacrificial electron donor decamethylferrocene (DcMFc) in a biphasic H2 evolution scheme using core‐shell semiconductor nanoparticles and phase transfer of the oxidised donor (DcMFc+).