A biofuel cell of (methyl violet/AuNPs)₂₅/FTO photoanode and bilirubin oxidase/CuCo₂O₄ bio-photocathode inspired by the photoelectrochemistry activities of fluorescent materials/molecules

Herein, we discuss the idea that fluorescent materials/molecules should logically show potential photoelectrochemistry (PEC) activity, and, in particular, the PEC of fluorescent small molecules (previously usually acting only as dye sensitizers for conventional semiconductors) is explored. After examining the PEC activities of some typical inorganic or organic fluorescent materials/molecules and by adopting methyl violet (MV) with the highest PEC activity among the examined fluorescent small molecules, a new and efficient (MV/Au nanoparticles (AuNPs))₂₅/fluorine-doped tin oxide (FTO) photoanode without conventional semiconductor(s) is prepared by layer-by-layer alternating the electrodeposition of AuNPs and the adsorption of MV. A bilirubin oxidase (BOD)/CuCo₂O₄/FTO bio-photocathode is prepared by electrodeposition, calcination and cast-coating. Under optimal conditions, a new photoelectrochemical enzymatic biofuel cell (PEBFC) consisting of this photoanode in 0.1 M phosphate buffer solution (PBS) containing 0.1 M ascorbic acid, this bio-photocathode in 0.1 M PBS containing 0.5 mM 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, and a Nafion membrane gives an open-circuit voltage of 0.73 V and a maximum power output density of 14.1 μW cm^-2, outperforming many reported comparable enzymatic biofuel cells. This fluorescence-activity-based PEC research suggests that new PEC and photocatalysis materials/molecules may be found from the huge library of fluorescent substances, and such a fluorescence-based reference criterion is of some general reference value for exploring potential photoelectric materials/molecules and expanding the applications of fluorescent substances.