Photosystem I Multilayers within Porous Indium Tin Oxide Cathodes Enhance Mediated Electron Transfer

Understanding and improving charge transfer pathways between extracted Photosystem I (PSI) protein complexes and electrodes is necessary for the development of low-cost PSI-based devices for energy conversion. We incorporated PSI multilayers within porous indium tin oxide (ITO) electrodes and observed a greater mediated photocurrent in comparison to multilayers on planar ITO. First, the mediated electron transfer (MET) pathway in the presence of 2,6-dichlorophenolindophenol (DCPIP) and ascorbate (AscH) was studied via photochronoamperometry on planar ITO. ITO nanoparticles were then used to fabricate two porous electrode morphologies; mesoporous (20-100 nm pores) and macroporous (5 mu m pores). PSI multilayers within macroporous ITO cathodes produced 42 +/- 5 mu A cm(-2) of photocurrent, three times the photocurrent produced by mesoporous ITO. Additionally, macroporous cathodes are able to utilize twice as much active surface area, when compared to mesoporous cathodes. Our findings show that MET within PSI multilayers is greater in 5 mu m macropores than mesoporous ITO due to both an increase in electrode surface area and the location of PSI complexes within the pores. Improving MET in PSI-based bioelectrodes has applications including improving the total charge transfer achieved in PSI-based photoelectrochemical cells or even incorporation in bio-photocatalytic cells.