Self-replicating Biophotoelectrochemistry System for Sustainable CO Methanation

Efficient conversion of CO-rich gas to methane (CH4) provides an effective energy solution by taking advantage of existing natural gas infrastructures. However, traditional chemical and biological conversions face different challenges. Herein, an innovative biophotoelectrochemistry (BPEC) system using Methanosarcina barkeri-CdS as a biohybrid catalyst was successfully employed for CO methanation. Compared with CO2-fed BPEC, BPEC-CO significantly extended the CH4 producing time by 1.7-fold and exhibited a higher CH4 yield by 9.5-fold under light irradiation. This superior conversion of CO resulted from the fact that CO could serve as an effective quencher of reactive species along with the photoelectron production. In addition, CO was used as a carbon source either directly or indirectly via the produced CO2 for M. barkeri. Such a process improved the redox activities of membrane-bound proteins for BPEC methanogenesis. These results were consistent with the transcriptomic analyses, in which the genes for the putative CO oxidation and CO2 reduction pathways in M. barkeri were highly expressed, while the gene expression for reactive oxygen species detoxification remained relatively stable under light irradiation. This study has provided the first proof-ofconcept evidence for sustainable CO methanation under a mild condition in the self-replicating BPEC system.