Electrocatalytic up-conversion of biogas CO2 using gas-diffusion electrodes with in-situ reconstructed bismuth oxide catalysts

초록

Electrochemical conversion of CO2 using gas diffusion electrodes (GDEs) offers a compelling route for biogas upgrading by simultaneously increasing methane (CH4) content and producing value-added chemicals. In this study, we develop Bi(OH)SO4 & sdot;H2O nanorods as electrocatalysts, synthesized via a simple, low-temperature coprecipitation method that offers excellent scalability and reproducibility. These catalysts, in situ transformed into Bi oxyhydroxides, demonstrate high activity and selectivity for formate production in alkaline media, even under dilute CO2 conditions representative of real biogas (-40% CO2 and-60% CH4). The optimized GDE system achieves a partial current density (JP) of up to-570 mA cm-2 and Faradaic efficiency (FE) exceeding 90% under pure CO2. Under 40% CO2, the system maintains a high FE with Jp of-130 mA cm-2 for formate production. Performance is strongly influenced by gas flow rate, revealing the need to balance CO2 availability and suppression of hydrogen evolution. A three-cell GDE configuration connected in series further enhances CO2 conversion efficiency, increasing methane content to-90% without requiring gas separation or pretreatment. Real biogas tests confirm the practical feasibility of the system, though the presence of H2S impacts early-stage performance, highlighting the importance of desulfurization. This work demonstrates a robust, modular strategy for decentralized biogas upgrading via CO2 electroreduction.

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