Efficient production of acetate from inorganic carbon (HCO₃^–) in microbial electrosynthesis systems incorporating Ag₃PO₄/g-C₃N₄ anaerobic photo-assisted biocathodes

The efficient production of acetate from HCO₃⁻ by the nonphotosynthetic bacterium Serratia marcescens Q1 is demonstrated in an anaerobic, photo-assisted, microbial electrosynthesis (MES) system incorporating a Ag₃PO₄/g-C₃N₄ biocathode. The Ag₃PO₄/g-C₃N₄ formed a Z-scheme photocatalytic heterojunction structure with enhanced redox capacity. The photocorrosion of Ag₃PO₄ was inhibited by the production of H₂O₂ in-situ, through water oxidation driven by the photogenerated holes on the Ag₃PO₄ valence band. The photoinduced electrons on the conduction band of g-C₃N₄ instead produced H₂, which was metabolized by the Q1 electrotroph with HCO₃⁻ to produce acetate at a rate of 5.4 mM/d with a CEacetate of 93 % at a current density of 3.3 A/m². The MES accumulated up to 81.0 mM with a CE_acetate of 89 % over 16 days continuous operation. This study provides a sustainable and feasible strategy for inhibiting the photocorrosion of Ag₃PO₄ and thus achieve efficient acetate production from HCO₃⁻ in photo-assisted MESs biocathodes.