Photoelectrochemical Characterization of Photosystem I Encapsulated in Nafion

As battlefield technologies continue to become more advanced and energy intensive, there is an increased cost and a higher exposure to hazards when supplying fuels to meet the power demand of these applications. This has created a great need to reduce the amount of energy delivered in the field, and has introduced a need for on-site fuel generation to reduce the logistical burden.

Solar derived fuels are a leading area of research for on-site fuel generation because of the ubiquity of solar energy. The biomimetic approach of converting solar to useful energy, simulating photosynthesis, employs the highly efficient photosynthetic protein Photosystem I (PSI) to reduce water to H₂ which would in turn be used to fuel combustion engines or fuel cells. Any device deployed in the field would need to be designed for portable applications. Therefore, a robust and electrochemically active electrode must be developed which allows PSI to access both light and aqueous electrolyte solutions.

This presentation relates recent work with encapsulating PSI and the redox mediator Os(bpy)₂Cl₂ in a Nafion polymeric film. Because of surface charges in Nafion’s water-filled pores both PSI and Os(bpy)₂Cl₂ are trapped in the polymer matrix whereas the positively charged methyl viologen (MV) redox mediator is able to diffuse through the film. The films are characterized for their stability and photoelectrochemical performance resulting in their capability to load PSI in the films at very high surface densities. The use of Nafion makes the film more stable than other redox polymers tested, and the high surface densities of PSI opens the door to higher photocurrents.