ZIF-8 confined carbon dots/bilirubin oxidase on microalgal cells to boost oxygen reduction reaction in photo-biocatalytic fuel cells for pollutants removal

Abstract

Photocatalytic fuel cells provide promising opportunities for sustainable wastewater treatment and energy conversion. However, their applications are challenged by the sluggish oxygen reducton reaction (ORR) kinetics at cathodes owning to the low O2 solubility and diffusion rate. Herein, we proposed a photo-biocatalytic fuel cell (PBFC) with a novel hybrid biocathode based on artificially engineered algal cells coated by ZIF-8 confined carbon dots/bilirubin oxidase (ZIF-8/CDs/BOD@algae). Microalgae absorbed CO2 and provided O2 in situ for BOD catalysts. Due to effective absorption of O2 by imidazole and confinement of hydrophobic porous ZIF-8, oxygen diffusion has been accelerated in MOF/enzyme systems. Importantly, the introduction of CDs alleviated the poor conductivity of ZIF-8 and improved the electron transfer rate of BOD. Thus, the biocathode exhibited a high current density of 1767 μA/cm2, a 2.26-fold increase compared with that of CDs/BOD/algae biocathode. Also, it displayed enduring operational stability for up to 60 h since the firmly wrapped ZIF-8 shells could encapsulate proteins and protect algae from the external stimulation. When coupled with Mo:BiVO4 photoanodes, the PBFC exhibited a remarkable power output of 131.8 μW/cm2 using tetracycline hydrochloride (TCH) as a fuel and an increased degradation rate of TCH. Therefore, this work not only establishs an effective confinement strategy for enzyme to enrich oxygen, but also unveils new possibilities for modified microalgal cells aiding photoelectrocatalytic systems to recover energy from wastewater treatment.