Recent advances in electrochemical carbon dioxide reduction strategies in biogas upgrading and biomethane production

Biogas upgrading technologies play a crucial role in purifying methane (CH₄), employing advanced processes to produce biomethane that meets natural gas grid-quality standards. Extensive research has been conducted on these technologies to maximize CH₄ content, the primary energy component in biogas, thereby enhancing its overall energy value and suitability for a variety of applications. This comprehensive review investigates emerging advances in electrochemical carbon dioxide (CO₂) reduction technologies, with a special emphasis on their application in converting CO₂ in biogas to biomethane. The study provides a critical analysis of the state of the art and potential future directions in this field, covering multiple aspects such as electrochemical reactors, catalyst development, electrode materials, operational conditions, understanding the mechanism, selectivity, sustainability assessments, and upscaling possibilities. Further, the performance of this biogas upgrading strategy under various operating conditions, especially fed batch and continuous mode, in conjunction with the innovative cathode materials, has been thoroughly evaluated and reviewed. The electrodes used conventionally in electrochemical CO₂ reduction for biogas upgrading include carbon-based materials such as carbon cloth, carbon paper, graphite rod, and carbon nanotubes, concurrently with metal electrodes like stainless-steel, titanium and copper (Cu). Albeit, gas diffusion electrodes (GDEs), Cu based electrodes such as Cu nanowires and nafion modified electrodes in continuous flow cell type reactors have demonstrated better performance in achieving higher current densities, supplying electrons for enhancement of CO₂ reduction to CH₄.