Fabrication of scalable and flexible bio-photoanodes by electrospraying thylakoid/graphene oxide composites

For extraction of photosynthetic electrons (PEs) from plant cells and algal cells, there have been many approaches using living algal cells or isolated photosynthetic apparatus such as photosystem II, photosystem I, and thylakoid membranes (TMs). Among these, bio-photoanodes coated with TMs demonstrated stable performance and the possibility for their practical applications. When a TM photoanode is prepared, TMs are deposited on the surface of a metal electrode. However, since the thickness of TM films determines the light absorption and electron transfer processes, the performance of a TM bio-photoanode is significantly affected by the TM film quality. Thus, in this study, electrospraying was employed to deposit TMs with enhanced control of the thickness and uniformity of TM coating on metal electrodes. In particular, we investigated how both the quality of TM films and the magnitude of PE currents were influenced by electrospraying time, substrate motion, solution feed rates, TM concentration, and addition of graphene oxide (GO) nanosheets. Finally, to assess the feasibility of TM electrospraying as a scalable fabrication method, TMs were electrosprayed on 5 × 5 cm ² size films of indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) (ITO-PEN). The coating uniformity was assessed by measuring PE currents from different locations of the TM-deposited ITO-PEN films.