(685c) Codesign of Multijunction Photoelectrochemical Devices for Unassisted CO2 Reduction to Multicarbon Products

Solar-driven CO₂ reduction (CO₂R) holds great promise for the sustainable generation of energy-dense fuels and chemicals. Multicarbon (C₂₊) products are particularly attractive because they have a large market size and can be further converted to higher molecular weight hydrocarbons fuels. Metallic Cu has the unique ability to catalyze CO₂ to C₂₊ products with high faradaic efficiency; however, the product distribution of CO₂R on Cu is potential-dependent. To achieve selective PEC CO₂R to C₂₊ products, the potential at which C₂₊ product formation is maximized, referred to here as V_id, needs to be attained. To obtain a sufficiently high photovoltage for operation near V_id, a photoelectrode with two or three semiconductors of different bandgaps in a multijunction stack is required. The photovoltage and photocurrent depends on the exact combination of bandgaps in the multijunction stack. In addition, V_id will depend on the overall device architecture because various overpotentials shift V_id.

This talk will present a continuum model of PEC CO₂R and will explore the codesign of the photoelectrode bandgaps and device architecture for the generation of C₂₊ products. The simulation results demonstrate the critical importance of simultaneously engineering the photoelectrode and device design in order to ensure the photovoltage and photocurrent from the photoelectrode enables operation at the device-specific V_id. Modifying the device design will require a change in operating potential in order to ensure the system operates at the new V_id, which can be achieved by changing all the bandgaps in the multijunction stack by approximately the same amount. In addition, the model predicts that photoelectrodes with a high photocurrent and photovoltage near V_id are required to achieve high solar-to-C₂₊ efficiency throughout the diurnal and annual solar cycles. This insight is critical for the design of monolithic, unassisted PEC CO₂R systems which yield high solar-to-C₂₊ efficiency.