FRET-guided surging of cyanobacterial photosystems improves and stabilizes current in photosynthetic microbial fuel cell

Abstract

Improving power generation under low light conditions and efficiently capturing electrons from the photosynthetic bacteria on the electrode are critical issues for developing a viable photosynthetic microbial fuel cell (PMFC). To address these issues, an anode was developed for a dual-chambered PMFC with an abiotic cathode, via casting a nanocomposite matrix comprising CdTe quantum dots (QD), graphene nanoplatelets (GNP) and silk-fibroin (SF) on a graphite electrode. The nanocomposite matrix supported biofilm growth of the photo-catalyst Synechococcus sp., surged the bacterial photosystems (PS I and PS II) with appropriate light (λ_{650–750 nm}) at a broad excitation spectrum (λ_{350–644 nm}) through fluorescence resonance energy transfer and facilitated the metabolic electron relay through direct electron transfer (DET) to the anode. The maximum current density of the PMFC obtained with the nanocomposite bioanode (1.89 A m⁻²) was ∼5.7 fold higher than that of the corresponding blank graphite anode. The positive effect of QD was further confirmed from the fading reversal of polarity during the circadian cycle, leading to sustained current generation in the PMFC. The GNP reduced the band gap of the nanocomposite to 2.9 eV and decreased the charge transfer resistance by ∼9 fold, thus enabling DET on the electrode, as is evident from a pair of redox peaks of the bioanode with the formal potential of −156 mV. Structural studies demonstrated the rational interactions of the hydrophobic β-sheet of the SF with the nanomaterials. An unprecedented light conversion efficiency of 4.01% for the cyanobacteria was achieved with the nanocomposite bioanode-based PMFC.