A Biophotocathode Based on Photosystem I with Record-High Photocurrent Density Coupled with Bioelectrochemical Glycerol Oxidation

Developing efficient semiartificial photosynthetic systems is crucial for sustainable solar energy conversion. Photosystem I (PSI) is an ideal photoactive component for such systems due to its ability to perform light-induced charge separation with near-perfect quantum efficiency. We report a high-performance PSI-based biophotocathode by immobilizing PSI in a poly(vinyl)imidazole-Os(bispyridine)2Cl (POs) redox polymer hydrogel within a translucent, three-dimensional (3D) porous indium tin oxide (ITO) scaffold. This hierarchical architecture synergistically enhances the PSI/redox hydrogel loading, promotes light harvesting, and facilitates rapid mediated electron transfer (MET), leading to record-breaking steady-state photocurrent densities of 4068 μA cm–2. An outstanding incident photon-to-current conversion efficiency (IPCE) of up to 61% is observed at a light intensity of 0.14 mW cm–2. To create a self-sustaining system, this advanced photocathode was integrated with a bioanode featuring galactose oxidase that efficiently oxidizes glycerol, a low-cost byproduct of the biodiesel industry. The resulting two-compartment photoelectrochemical (PEC) cell operates as a biophotovoltaic cell, exhibiting an open-circuit voltage of 0.42 V and a maximum power density of 18.5 μW cm–2. This work not only presents a significant advancement in the performance of PSI-based biophotocathodes but also demonstrates a viable pathway for semiartificial photosynthetic systems that simultaneously convert solar energy and valorize a waste stream chemical.