Harnessing photosynthesis for solar energy conversion

Dvir Harrisa‡, Volker Hartmannb‡, Adrian Ruffc, Marc M. Nowaczykb, Wolfgang Schuhmannc, Matthias Rögnerb, Noam Adira
Equal contribution
aGrand Technion Energy Program, Schulich Faculty of Chemistry, Technion, Haifa 32000, Israel; bPlant Biochemistry, Faculty of Biology & Biotechnology, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany; cAnalytical Chemistry and Center for Electrochemical Science – CES, Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany

The phycobilisome (PBS), a protein-pigment complex that can reach 7 MDa has been researched tremendously throughout the past 50 years. However, it has yet to be implemented in synthetic applications that can use its extraordinary energy absorption capabilities. In the research presented here, a first-ever PBS-containing solar cell will be presented.

PBS was isolated from various organisms and incubated in-vitro with isolated photosystem 2 (PSII) from the thermophilic cyanobacteria Thermosynecchococus elongates. PSII is a 500KDa protein-pigment complex that performs water oxidation using its oxygen evolving complex (OEC). To strengthen the PBS-PSII super-complex interaction, chemical cross-linking (covalently binding adjacent protein entities using a bi-dentate molecule) was applied.  The cross-linked super-complex functionality was monitored using spectroscopic and electrochemical tools.
Enhancement of photocurrent obtained via the PBS-PSII complex was achieved via a conductive osmium-containing polymer (poly(vinyl)imidazole Os(bispyridine)2Cl). The polymer is potential-tuned to fit electrons shuttling towards the electrode in a potential gradient. The polymer increases the surface-to-volume ratio significantly by entangling the super-complex in a “meatball in spaghetti” fashion, thus providing 3D encapsulation.

We aim to continue investigating the resulted cross-linked PBS-PSII mega-complex using various tools such as electron microscopy, gel electrophoresis and X-ray crystallography. Additionally, the phylogenetic query regarding cross-species incubation of PBS and PSII should be further examined.  Finally, the presented anodic half-cell would be coupled to a cathodic half-cell, using its reductive potential for fuel production (for instance, H+ to H2 using the enzyme hydrogenase or inorganic catalysts).