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Potential-controlled assembly of photocatalysts in aqueous colloidal suspensions at two water-oil interfaces + a Z-scheme architecture allow for efficient water splitting.
About
Our device is based on a double liquid-liquid interface (DLLI, see figure). The aqueous solution on the left contains negatively charged colloidal particles of a photocatalyst active for water oxidation, while the aqueous solution on the right contains positively charged colloidal particles of a photocatalyst active for water reduction. Polarising the aqueous solution on the left negatively with respect to the aqueous solution on the right will drive the assembly of the colloidal particles at the respective interfaces, which will have inverse polarisations, as illustrated in the figure. Polarisation will be achieved by applying an adequate voltage difference between the two aqueous phases, but after an initial current transient and charging of the interfaces, the current flowing through the external circuit (and, hence, the power consumption) will be zero. Illumination of the interfaces will lead to generation of electron-pair holes, whereby capture of the hole by water and generation of oxygen will occur at the liquid-liquid interface on the left while capture of the electron by water and generation of hydrogen will occur at the liquid-liquid interface on the right. The unused electron and hole, respectively, will be transferred to a redox couple (e.g. Fc/Fc+ or TCNQ/TCNQ-) in the organic phase connecting the two aqueous phases. This system will also allow for separation of photogenerated H2 and O2 in different compartments. For the circuit to be closed there also needs to be proton transport between the two aqueous compartments, which will be achieved by placing a proton-conducting membrane (e.g., Nafion®) between them. This DLLI setup can be adapted for other reactions, like the hydrogenation of CO2 or of N2 to hydrocarbons or ammonia, respectively.
Key Benefits
The innovation will allow to increase the efficiency of solar water splitting as comp.ared with current photocatalytic system. The process is analogous to natural photosynthesis and will allow to reach the theoretical limit of efficiency of Z-scheme systems (40%, although existing systems based on Z-scheme do not reach 10%). The main advantages of our innovation compared with current Z-scheme-based systems are: (i) assembly of photocatalyst at an interface within an electric field reduces rate of recombination of photogenerated electrons and holes; (ii) separation of the generation of hydrogen and oxygen.
Applications
Storage of solar energy as hydrogen (i.e., production of a solar fuel).