Light-Harvesting Proteins and Biofilms on Iron Oxide Photoelectrodes
The first bio-hybrid electrodes were used by Melvin Calvin in the late 1950s where he sublimated chlorophyll on aquadag graphite interdigital electrodes. This was done merely to study the bio-organic material. Helmut Tributsch' dye-sensitized solar cells (DSSC) in the early 1970s were ZnO electrodes, i.e. semiconductors further functionalized with natural absorbing dye molecules. Since, DSSCs have developed as a field in photovoltaic solar energy conversion technology. Meanwhile, photoelectrodes for solar water splitting in photoelectrochemical cells (PEC) evolved as an independent field. This field has recently emerged again and is virtually taking center stage. Also here, functionalization of traditional semicondcutor electrodes with bio-organic motifs is gaining more and more interest. Hydrogenase is a frequently used protein for the promotion of hydrogen evolution on photocathodes. We have recently coated the light harvesting antenna protein C-phycocyanin on iron oxide photoelectrodes. This approach was quite promising. We measured an increrased photocurrent density at the photoanode and an increased hydrogen evolution at the counter electrode. During our studies we were pointed to the question of charge transfer across the bio-electronic interface which is formed by biomolecules and metal oxides. Because the expressioan and purification of C-phycocyanin, which is extracted from cyanobacteria, is a costly and laborious process, we explored also the use of complete cyanobacteria on the photoelectrodes. The thylakoid membrane and cell membrane may pose electrical barriers between the biocatalytic or light harvesting components in the photosynthetic apparatus and the semicondcutor electrode underneath. It is therefore necessary to quantify this barrier. For this, we are performing electroanalytical experiments and x-ray spectroscopy experiments operando and in situ, in the latter case with an actual anabaena biofilm with ambient pressure XPS on a bio-electrochemica cell.
 J. Ihssen, A. Braun, G. Faccio, K. Gajda-Schrantz, L. Thöny-Meyer; Light harvesting proteins for solar fuel generation in bioengineered photoelectrochemical cells; Current Protein and Peptide Science, 2014, 15 (4),374-384.
 D. K. Bora, Y. Hu, S. Thiess, S. Erat, X. Feng, S. Mukherjee, G. Fortunato, N. Gaillard, R. Toth, K. Gajda-Schrantz, W. Drube, M. Grätzel, J. Guo, J. Zhu, E.C. Constable, D.D. Sarma, H. Wang, A. Braun, Between Photocatalysis and Photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation, J. Electron Spectr. Rel. Phenom. 2013, 190 A, 93-105.
 D.K. Bora, A.A. Rozhkova, K. Schrantz, P.P. Wyss, A. Braun, T. Graule, E.C. Constable, Functionalization of Nanostructured Hematite Thin-Film Electrodes with the Light-Harvesting Membrane Protein C-Phycocyanin Yields an Enhanced Photocurrent, Advanced Functional Materials 2012, 22 (3) 490-502.
 D.K. Bora, A. Braun, E.C. Constable, “In rust we trust”. Hematite the prospective inorganic backbone for artificial photosynthesis, Energy Environ. Sci., 2013,6, 407-425.
 A Braun, F. Boudoire, D. K. Bora, G. Faccio, Y. Hu, A. Kroll, B. S. Mun, S. T. Wilson, Biological components and bio-electronic interfaces of water splitting photo-electrodes for solar hydrogen production, Chem. Eur. J. 2015, 21(11), 4188-4199.