Hierarchical Conductors Unlock Scaling of ePTFE-Based CO₂ Conversion Electrodes

Gas Diffusion Electrodes (GDEs) for electrochemical CO₂ conversion must maintain robust hydrophobicity to prevent flooding, while also ensuring high conductivity to minimize ohmic losses. Conventional GDEs are limited by intrinsic material tradeoffs: carbon paper is highly conductive but floods easily, while expanded PTFE (ePTFE) is flooding resistant but non-conductive. Though many of the most promising systems to date demonstrate high conversion selectivity with ePTFE GDEs, their lack of through-plane conductivity has limited electrode sizes to just ~5 cm². We devise a finite element model which captures the ohmic losses and associated variations in product distribution across ePTFE electrodes which then informs rational electrode conductivity requirements. We then present our Hierarchically Conductive GDE architecture (HCGDE) which employs microscale conductors woven within an ePTFE membrane to overcome the size limitation, achieving C₂₊ Faradaic efficiencies of ~75% for electrodes as large as 50 cm². Our approach can be broadly applied to scale any electrode, independent of catalyst chemistry and morphology.