Photosystem-Based Biophotoelectrodes for Solar Energy Conversion

Photosystem-modified electrodes have been developed as alternatives to classical semiconductor-based systems for solar energy conversion into chemicals or electricity. Photosystems, the photoactive proteins of natural photosynthesis, offer exceptional light-harvesting efficiency and large charge separation and are composed entirely of earth-abundant elements. Their main limitations remain their limited robustness and difficulty of efficiently interfacing them with electrodes. Here, we review the strategies for integrating the three major classes of photosystems (photosystem II, photosystem I, and bacterial reaction centers) into functional devices. We examine electrode architectures such as biophotoanodes and biophotocathodes as well as their assembly into biased and bias-free biophotoelectrochemical cells using various protein immobilization approaches aimed at maximizing photocurrent and energy efficiency. Particular emphasis is placed on understanding electron-transfer pathways between electrodes and photosystems, including potential short-circuiting pathways. Finally, we highlight key characterization tools and performance metrics that are essential for identifying bottlenecks and guiding optimization.