Developing Z-Scheme Photocatalysts for the Selective Reduction of Carbon Dioxide

Description

Carbon dioxide (CO2) recycling is a key technology to determining the fate of fossil fuels utilization in the near future, as the intersecting issues of rising energy demand, global warming and energy economics become increasingly critical. The race is on to develop different means of sustainable CO2 reduction, which ultimately forms an inseparable technology to fossil fuel burning. The proposal seeks to develop artificial photosynthesis through the Z-scheme assembly of semiconductor photocatalysts, with the aim of chemically reducing CO2 back to fuel using solely water and sunlight. This involves the coupling of metal oxide photocatalysts which valence band potential is sufficiently positive to oxidize water, and quantum dot (QD) photocatalysts which conduction band potential is more negative than that required for CO2 reduction. The biggest advantage of such Z-scheme photocatalysts, as opposed to a single photocatalyst construct, is the ability to combine a large library of photocatalytic materials that readily meets either one of the two band potential requirements. There are 5 core components that make up the Z-scheme photocatalyst, namely, oxygen evolution cocatalyst (OEC), the metal oxide photocatalyst, electron mediator, the QD photocatalyst, and CO2 reducing cocatalyst (CRC). Except for the design OEC, which is considered a solved challenge with the recent discovery of highly efficient cobalt phosphate and IrO2, the proposal focuses on the systematic development of the other components. Here, the selection of model oxide photocatalysts to be studied includes TiO2, ZnO, SnO2, SrTiO3, WO3, Fe2O3 and BiVO4 in their pristine and doped forms. Likewise, the range of QD photocatalysts includes CdX, PbX (X = S, Se, Te) and CuInS2, which CB potentials and bandgaps can be easily tuned through precise crystal size control. Different electron mediating strategies will be explored including that of direct physical coupling, and via graphene, noble metal or aqueous-dissolved ionic mediators. A novel CRC design based on basic metal oxide that is capable of high activity and selectivity towards CO2 reduction (as opposed to H2 evolution) is also proposed. The Z-scheme photocatalysts will be assessed under simulated solar irradiation, while the fundamental charge transport studies and mechanism of CO2 reduction will be assessed in relation to the overall Z-scheme architecture. Success of the proposal will lead to a new class of solar-activated and selective CO2 reduction photocatalysts.