Co-Design of Multijunction Photoelectrochemical Devices for Unassisted CO₂ Reduction to Multicarbon Products

Photoelectrochemical (PEC) CO2 reduction (PEC CO2R) is a prospective approach for utilizing solar energy to synthesize a variety of carbon-containing chemicals and fuels, the most valuable of which are multicarbon (C2+) products, such as ethylene and ethanol. While these products can be produced with high faradaic efficiency using Cu, this occurs over a relatively narrow potential range, which, in turn, imposes constraints on the design of a device for PEC CO2R. Herein, we used continuum-scale modeling to simulate the solar-to-C2+ (STC2+) efficiency of PEC CO2R devices fed with CO2-saturated, 0.1 M CsHCO3. We then explored how cell architecture and the use of single or dual photoelectrode(s) alters the optimal combination of photoelectrode bandgaps for high STC2+ efficiency. Ultimately, this work provides guidance for the co-design of the device architecture and photoelectrode bandgaps required to achieve high STC2+ efficiency. The insights gained are then used to identify systems that yield the highest amount of C2+ products throughout the day and year.