UC Berkeley

There is increasing interest in the possibility of photoelectrochemical (PEC) reduction of CO2to 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 CO2reduction (CO2R) on Cu in 0.1 M CsHCO3and 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 Vidand low series resistance. The STC2+rate in these systems is enhanced by optimal CO2transport and exhibits low sensitivity to dirunal solar irradiance variations.