Development of flow-through microtubular gas-diffusion electrodes for electrochemical CO2 reduction

Development of flow-through microtubular gas-diffusion electrodes for electrochemical CO2 reduction

Electrochemical reduction of CO2 (CO2RR) into value-added products offers a promising strategy to reduce dependence on fossil fuels, particularly when powered by renewable electricity. However, CO2RR faces challenges, including high activation energy barriers, competing side reactions, and limited CO2 mass transport. Addressing these limitations requires not only the development of advanced electrocatalysts but also the design of electrodes. 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 towards 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) 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. Therefore, studies have been conducted by engineering nano-structured electrocatalysts on Cu hollow fiber gas diffusion electrodes for electrochemical conversion of CO2. We begin with electrocatalyst tailoring to tune the selectivity of Cu HFGDE, including the synthesis of crystal facet-orientated zinc nanosheets for syngas production and hierarchical AgZn bimetallic catalysts for selective CO production. To address the low limited pore utilization inherent to HFGDEs, we employ a facile strategy to manipulate the surface wettability of the electrodes, enhancing CO2 distribution, optimizing triple-phase boundaries, and boosting CO2RR kinetics. Finally, to underscore the crucial role of CO2 availability under high current density and leverage the superior mass transport characteristics of HFGDE architectures, a flow-through HFGDE featuring in-situ grown defect-rich silver nanosheet catalysts is developed. This work highlights the rational design of flow-through HFGDE to maximize desired conversion under industrially relevant conditions.

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