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Efficient Photoelectrochemical Transformation of CO2 to Useful Fuels on Nanostructured Hybrid Electrodes

Periodic Reporting for period 2 - HybridSolarFuels (Efficient Photoelectrochemical Transformation of CO2 to Useful Fuels on Nanostructured Hybrid Electrodes)

Reporting period: 2018-07-01 to 2019-12-31

Given that CO2 is a greenhouse gas, using the energy of sunlight to convert CO2 to transportation fuels (such as methanol) and basic chemicals (such as syngas) represents a value-added approach to the simultaneous generation of alternative fuels and environmental remediation of carbon emissions. Photoelectrochemistry has been proven to be a useful avenue for solar water splitting. CO2 reduction, however, is multi-electron in nature (e.g. 6 e- to methanol) with considerable kinetic barriers to electron transfer. It therefore requires the use of carefully designed electrode surfaces to accelerate e- transfer rates to levels that make practical sense. In addition, novel flow-cell configurations have to be designed to overcome mass transport limitations of this reaction. We are going to design and assemble nanostructured hybrid materials to be simultaneously applied as both adsorber and cathode material to photoelectrochemically convert CO2 to valuable products. The three main goals of this project are to (i) gain fundamental understanding of morphological-, size-, and surface functional group effects on the PEC (PEC) behavior at the nanoscale (ii) design and synthesize new functional hybrid materials for PEC CO2 reduction, (iii) develop flow reactors for PEC CO2 reduction. Rationally designed hybrid nanostructures will be responsible for: (i) higher photocurrents due to facile charge transfer and better light absorption (ii) higher selectivity towards the formation of targeted products due to the adsorption of CO2 on the photocathode (iii) better stability of the photocathode. The challenges are great, but the possible rewards are enormous: performing CO2 adsorption and reduction on the same system may lead to PEC cells which can be deployed directly at the source point of CO2, which would go well beyond the state-of-the-art.
The project focuses on the direct photoelectrochemical (PEC) conversion of carbon dioxide to useful products. We vigorously study the effect of size, morphology, and surface functional groups of the photoelectrodes at the nanoscale. As a first step, we designed model systems to deconvolute the effect of the three main processes (light absorption, charge carrier transport and charge transfer), which dictate the solar-to-fuel conversion efficiency in a PEC cell. We studied bimetallic oxides, metal halide, lead halide perovskites in this vein. As the next step, we assembled hybrid photoelectrodes, where different components are responsible for the different processes. For example, nanocarbon-containing photoelectrodes outperformed their bare SC counterpart, due to enhanced charge carrier transport. We have developed and adapted different in situ electrochemical methods, to better understand the light-induced processes both inside the SC photoelectrodes, as well as at the SC/electrolyte interface. Finally, we designed, prepared and studied PEC flow cells to achieve unprecedentedly high CO2 conversion efficiencies. We have published over 18 high impact papers so far, in internationally leading journals.
So far, we have gone beyond the state-of-the-art from at least two aspects. We have developed and employed an in situ ultrafast spectroelectrochemistry method to understand the charge carrier dynamics of perovskite photoelectrodes under electrochemical control. This allows to better understand chemical events occurring upon irradiation. Elaborating on this tool, we can now rationally design new efficient and stable photoelectrodes for CO2 conversion.
We have designed, fabricated and validated novel electrochemical and photoelectrochemical cell architectures. These cells operate with direct CO2 gas feed, and generate different gas products. During the project, we are going to test different photoelectrode assemblies in these cells, to find the best candidate both in terms of efficiency and stability.