Selective Branching of Plasmonic Photosynthesis into Hydrocarbon Production and Hydrogen Generation

Abstract

Electrocatalytic and photocatalytic carbon fixation suffer from a major challenge: the undesirable hydrogen evolution reaction (HER) typically outcompetes the CO2 reduction reaction (CO2RR), amounting to a loss of energetic charge carriers and a reduced selectivity for hydrocarbon production. Likewise, hydrocarbon production by the CO2RR and hydrogen generation by the HER constitute competing pathways in plasmon-excitation-driven photosynthesis on Au nanoparticles promoted by an ionic liquid medium. Here, we measure the selectivity between these two reduction pathways under various reaction conditions. We show that the branching between the HER and CO2RR pathways can be tuned by controlling the proton availability in the medium. We identify conditions at which the CO2RR effectively outcompetes the HER: 84% of harvested electrons are utilized selectively for hydrocarbon production, whereas the HER branch is suppressed. The greater implication of this work is that reaction selectivity can be overturned by the utilization of plasmonic excitation and optimization of the solid–solution interfacial environment.