Direct Imaging of Local pH Reveals Bubble-Induced Mixing in a CO₂ Electrolyzer

Electrochemical CO2 reduction poses a promising pathway to produce hydrocarbon chemicals and fuels without relying on fossil fuels. Gas diffusion electrodes allow high selectivity for desired carbon products at current density by ensuring sufficient mass transfer rate the catalyst layer. In addition transfer, product also strongly depends local pH surface. this work, we directly visualize first time two-dimensional (2D) profile in catholyte channel of gas-fed electrolyzer equipped with bipolar membrane. The is imaged operando fluorescence lifetime imaging microscopy (FLIM) using pH-sensitive quinolinium-based dye. We demonstrate that bubble-induced mixing plays an important role Faradaic efficiency. Our concentration measurements show remains lower −100 mA cm–2 than −10 cm–2, implying advection outweighs additional OH– flux these densities. prove buffering effect from gas feed dissolved prevents electrode becoming alkaline. findings suggest electrolyzers membrane flowing are designs scale-up high-current-density operation because they able avoid extreme values