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

Abstract

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.