Self-Assembled Hybrid Structure of Natural Photosystems in Bio-Photovoltaic Cells for Enhanced Photoelectric Current Generation

In the natural photosynthesis of plant or cyanobacteria, functional proteins and redox cofactors are sophisticatedly self-assembled in the thylakoid membrane, exhibiting nearly 100 % of light-harvesting quantum efficiency. Photosystem I (PSI) is an integrated membrane protein complex that catalyzes the transfer of electrons using light energy. The photon energy absorbed by PSI also provides a proton motive force used to produce organic compounds. This finding has inspired engineers to pursue biomimetic and bio-inspired designs for efficient light-harvesting and charge extraction. However, the efficiency of nano-bio hybrid photosystems is often limited by the poorly-oriented assembly of photosystems with nanomaterials. In this work, we assembled PSI with protonated-carbon nitride (PCN) nanosheets through balanced intermolecular interactions, resulting in linker-free PSI/PCN hybrid nanostructures that generate favorable electronic interfacial structures for charge transfer through a Z-scheme system. Surface-modified carbon nitrides can provide photocatalytic activity under visible light irradiation conditions and a new electron transfer path in the hybrid structure with PSI. Electrostatic hybridization between protonated sites on the PCN nanosheets and the partially negatively charged lumen side of PSs provides a favorable orientation for efficient electron transfer. The PSI/PCN hybrids exhibit a photocurrent density more than 28 times higher than randomly oriented PSI. We also show that when coupling the developed bio-photocathode with a PSII-based photoanode, a photocurrent of 7.7 μA cm^-2 under bias-free conditions and a cell power up to 0.9 μW cm⁻² can be achieved. This study provides a vital strategy to construct an efficient biochemical photoelectrode based on natural photosystems coupled with semiconductor carbon nanostructures through simple self-assembly in a favorable orientation for efficient and stable interfacial electron transfer. This work was supported by Nano●Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2017M3A7B4052797).