Engineering Flow-Through Hollow Fiber Gas-Diffusion Electrodes for Unlocking High-Rate Gas-Phase Electrochemical Conversion.

Designing advanced electrodes with efficient contact with gas, electrolytes, and catalysts presents significant opportunities to enhance the accessibility of concentrated gas molecules to the catalytic sites while mitigating undesirable side reactions such as the hydrogen evolution reaction (HER), which advances the gas-phase electrochemical reduction toward industrial-scale applications. Traditional planar electrodes face challenges, including limited gas solubility and restricted mass transport. Although commercial flow-by gas-diffusion electrodes can reduce mass transfer resistance by enabling direct diffusion of gas molecules to active sites, the reliance on diffusive gas flow becomes insufficient to meet the rapid consumption demands of gas reactants at high current density. Flow-through hollow fiber gas-diffusion electrodes (HFGDEs) or hollow fiber gas penetration electrodes (HFGPEs) provide a promising solution by continuously delivering convective gas flow to active sites, resulting in enhanced mass transport and superior gas accessibility near the catalytic sites. Notably, HFGDEs have demonstrated the ability to achieve current densities exceeding multiple amperes per square centimeter in liquid electrolytes. This review provides a comprehensive overview of the design criteria, fabrication methods, and design strategies for porous metallic HFGDEs. It highlights the state-of-the-art advancements in HFGDEs composed of various metals (e.g., Cu, Ni, Ag, Bi, Ti, and Zn), with a particular focus on their utilization in the electrochemical conversion of CO. Finally, future research directions are discussed, underscoring the potential of porous metallic HFGDEs as a versatile and scalable electrode architecture for diverse electrochemical applications.