(Invited) Rational Design of Hybrid Photoelectrode Assemblies for Solar Fuel Generation

Abstract

Given that CO2 is a greenhouse gas, using the energy of sunlight to convert CO2 to fuels (such as methanol or methane) or basic chemicals represents a value-added approach to the simultaneous generation of alternative fuels and environmental remediation of carbon emissions. Electrochemistry and photoelectrochemistry have 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 this talk I will present some collaborative work, carried out together with Prof. Rajeshwar, on hybrid photoelectrodes leading to enhanced efficiency, selectivity, and stability. First, I will present the use of electrosynthetic (and photoelectrosynthetic) methods for preparing semiconductors on nanocarbon-modified electrode surfaces. Composites of nanocarbons with both inorganic and organic semiconductors represent an interesting class of new functional materials. Therefore, I will show how electrodeposition can be used to tune composition, crystal structure, and morphology of the nanocomposites for targeted applications. In the second part of my talk, I will focus on how to use semiconductor/nanocarbon hybrid materials for the photoelectrochemical reduction of CO2. Carbon nanotubes and graphene (either alone, or as building blocks of organized 3-D superstructures) can facilitate enhanced charge transport property for the photoelectrodes. I will present examples for Cu2O, TiO2, and Fe2O3-based electrodes, where the nanocarbon-containing photoelectrodes outperformed the pure semiconductor counterparts, both in terms of the achieved current densities and stability. Taking these observations together, as a general model will be presented on the role of the nanocarbon scaffold.