Establishing the Role of Operating Potential and Mass Transfer in Multicarbon Product Generation for Photoelectrochemical CO2
There is increasing interest in the possibility of photoelectrochemical (PEC) reduction of CO2 to C2+ products; however, the criteria for maximizing PEC solar-to-C2+ (STC2+) rates are not well understood. We report here a continuum-scale model of PEC CO2 reduction (CO2R) on Cu in 0.1 M CsHCO3 and use it to optimize the design and operating conditions for generating C2+ products. We demonstrate that the potential-dependent product distribution of CO2R on Cu requires operating near the potential that maximizes C2+ generation rates (Vid), unlike PEC water splitting, which desires operation at the maximum photocurrent density. Because of this requirement, the criterion for a high STC2+ rate includes high-photocurrent semiconductors with photovoltages near Vid and low series resistance. The STC2+ rate in these systems is enhanced by optimal CO2 transport and exhibits low sensitivity to dirunal solar irradiance variations.