Codesign Principles for the Generation of Multicarbon Products by Photovoltaic-powered CO₂ Reduction in a Membrane-Electrode Assembly

Photovoltaic-powered membrane-electrode assemblies (PV-MEAs) offer an intriguing approach for the conversion of CO2 into highly valuable multicarbon (C2+) chemicals, such as ethylene, ethanol, and propanol. However, a major limitation for this architecture is its low solar-to-C2+ product (STC2+) efficiency. To understand and overcome the limitations in STC2+ efficiency, a multiphysics model is developed and used to codesign the configuration of the photovoltaic (PV) element and the catalyst layer in the MEA to maximize STC2+ efficiency. We found that five silicon solar cells connected in series delivers sufficient photovoltage to drive the conversion of CO2 into C2+ products with ∼39% STC2+ efficiency, whereas multijunction solar cells can only attain an STC2+ efficiency of ≲5% because either the photovoltage or the photocurrent is too low for the electrolyzer, leading to the current–voltage curves intersecting at potentials that favor the formation of H2 and single-carbon products over C2+ products. Low STC2+ efficiencies are caused by high activity for the competing H2 evolution reaction (HER) at low cell potentials (<3.1 V). This can be suppressed by engineering the catalyst-layer active area and thickness, thereby increasing the PV-MEA operating potentials and, hence, the STC2+ efficiency. By implementing these strategies for the Cu catalyst investigated, we predict that PV-MEA devices can achieve STC2+ efficiencies as high as ∼46%. Even higher STC2+ efficiencies can be achieved by altering the catalyst microenvironment to minimize the rate of the HER vs CO2R. This work highlights PV-MEA designs that can enable the production of C2+ products from CO2, water, and sunlight.