Photosystem II-Carbon Nitride Photoanodes for Scalable Biophotoelectrochemistry

Photosystem II (PSII) is a vital photosynthetic enzyme with the potential for sustainable bioelectricity and fuel generation. However, interfacing PSII with intricate, small-scale electrodes for practical applications has been challenging. This study addresses this by creating protonated macroporous carbon nitride (MCN) as support and developing a scalable spray-freeze method to wire PSII with MCN. This facilitates the production of large-area MCN-PSII photoanodes up to 33 cm² for biophotoelectrochemical water oxidation to O₂, achieving efficient interfacial charge transfer and initial photocurrents in the mA range with Faradaic yield of 93.5 ± 8.5% over 5 h. A bias-free biophotoelectrochemical (BPEC) device is designed by connecting the MCN-PSII photoanode to a carbon nanotube cathode loaded with bilirubin oxidase. An array of eight tandem BPEC cells with a photoactive area of 72 cm² successfully powers low-power electronics, such as LEDs. This work paves an efficient way for bioelectrode fabrication, showcasing the potential of PSII-based semi-artificial systems for BPEC and biophotovoltaic applications.