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

[Display omitted] •Ag3PO4/g-C3N4 and S. marcescens catalyze acetate production in photo-assisted MES.•H2O2 produced in-situ under anaerobic conditions prevents photoetching of Ag3PO4.•Ag3PO4/g-C3N4 Z-scheme heterojunction enhances electron-holes separation.•Photo-induced electrons on conduction band of semiconductor enhances H2 production.•Photo-generated holes favors higher current and higher rates of acetate production. 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 CEacetate 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.