A Zero-Gap Gas Phase Photoelectrolyzer for CO₂ Reduction with Porous Carbon Supported Photocathodes

A modified Metal-Organic Framework UiO-66-NH₂-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO₂ reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH₂ catalyst. The highest energy-to-fuel conversion efficiency of 1.06% towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the electrodes in photoelectrochemical electrolyzers can impact the CO₂ reduction efficiency and selectivity.