Highly efficient and photostable conversion of bicarbonate to acetate by a pyrrolic nitrogen enriched Ag3PO4/g-C3N4 photocathode with an intermediate band level in photo-assisted microbial electrosynthesis systems

A highly efficient and photostable acetate production from bicarbonate (HCO3−) reduction is demonstrated in a photo-assisted microbial electrosynthesis system (MES) using a pyrrolic nitrogen enriched Ag3PO4/g-C3N4 photocathode. Urea-treatment of the Ag3PO4/g-C3N4 photocathode synergistically improved the MES performance by up to 1.8 folds under visible light illumination, achieving acetate production of 9.6 mM/d with coulombic efficiency of 95%, negligible catalyst leaching, and solar-to-acetate efficiency of 1.15% over 12 days continuous operation. The photocorrosion of Ag3PO4 was efficiently inhibited by a two-step charge transfer process mediated by an intermediate band level introduced by oxygen-vacancies in the Ag3PO4 structure, which also facilitated light absorption and charge transfer through a Z-scheme mechanism, whereas the increased pyrrole N in the g-C3N4 provided supplementary active sites for direct and indirect (via H2) electron transfer to Serratia marcescens electrotroph. This study demonstrates the ingenious use of photocatalytic heterojunctions for achieving step-changes in the MES performance.