Engineered photoelectrochemical interfaces induced electron bridging enables efficient CO2 to acetate electrosynthesis

Microbial electrosynthesis (MES) offers a promising platform for sustainable CO₂ conversion, yet remains constrained by inefficient electron utilization. In this study, a photo-assisted MES (PMES) platform was developed by introducing cationic CdS@PDDA nanorods into the cathodic environment to construct light-responsive nano-bio interfaces. Compared to conventional MES, the PMES system exhibited a 64 % increase in current density and a 55.6 % enhancement in acetate production, reaching approximately 10 g/L. Electron flux partitioning and electrochemical analyses revealed that CdS@PDDA nanorods reconfigured the electron delivery pathway by diverting over 30 % of cathodic electrons from electrode-bound biofilms to suspended microbial populations. Direct electron transfer, facilitated by the engineered interface, accounted for 73 % of the electron uptake by suspended cells, corresponding to a cumulative charge input of 2893.51 C. This spatial redistribution significantly accelerated extracellular electron transfer and expanded the catalytic domain beyond the biofilm region. Control experiments confirmed that photogenerated electrons contributed less than 9 % of total acetate yield, underscoring the dominant role of photoelectrochemical synergistic catalysis. Mechanistically, the redistributed electron flow was attributed to the photoelectrochemical interface, which promoted more reduced EPS and microbial surface redox states, thereby facilitating direct electron transfer. These findings demonstrate that the CdS@PDDA nanorods function as effective electron bridges, enabling spatially distributed, H₂-independent electron delivery, as confirmed by the fact that hydrogen contributed less than 10 % to acetate production. This strategy addresses long-standing spatial bottlenecks in MES and offers a promising interface design for efficient CO₂-to-acetate conversion under mild conditions. • CdS@PDDA enabled single-cell interface engineering to construct a photo-assisted MES. • CdS@PDDA acted as electron bridge, redirecting electron flux toward suspended microbes. • PMES boosted acetate production by 55.6 % mainly via actives suspended microbes. • EPS secretion and ferricyanide reduction confirmed improved electron transfer. • PMES enriched homoacetogens and upregulated CO₂ fixation-related genes.