Enhancing Biocathode Functionality in Bioelectrochemical Systems Using Poly(ethylene oxide) Hydrogel Coatings

Bioelectrochemical systems (BES) have emerged as sustainable platforms for CO2 valorisation and renewable energy production, but their efficiency is often limited by slow biocathode start-up. A promising route to create more efficient BES is the use of removable hydrogels to improve microbial adhesion. In this work, the influence of new coating biocathodes on poly(ethylene oxide) hydrogels for improved bioelectrochemical systems was evaluated. Hydrogels with different concentrations of poly(ethylene oxide) (5, 10, and 15 wt %) were evaluated as electrode coating. In addition, their effect on initial cell adhesion, microbial proliferation and productivity were studied. The results showed that 10 wt % PEO produced the most suitable coating, combining homogeneous pore structure, adequate elastic modulus and controlled detachment within 5 days. When applied to pretreated carbon felt, the hydrogel increased current density by 37.4% compared with uncoated electrodes, accelerated the start-up period, and promoting higher methane production. At steady state, the hydrogel-coated biocathode directed more carbon into methane (26 vs 3% respect to control) and reduced the unconverted carbon fraction (41 vs 65% respect to control). Microbial community analysis revealed selective enrichment of Methanobacterium, indicating a hydrogenotrophic pathway consistent with the applied potential. In conclusion, this study has made it possible to improve the start-up of the bioelectrochemical systems, demonstrating the potential of hydrogels in the start-up of these systems.