(Invited) Biohybrid Photoelectrodes Exploiting Effective Photosystem I - Electrode Contacts

Abstract

Hybrid systems using the unique features of natural photosynthesis are increasingly in the focus of current research. Particularly the two protein complexes photosystem I and II (PS) of the oxygenic photosynthesis have attracted the attention of researchers to build up new solar energy-converting systems. In such biohybrid systems an efficient coupling of PS with the electrode is essential. Besides the light-to-current conversion, the PS may also be used for light-driven enzymatic reactions resulting in photobioelectrocatalysis. Different basic principles can be used by establishing communication between the PS and electrode surfaces. Here we want to avoid shuttle molecules and generate a surface allowing direct electron transfer (DET) between the excited protein and the electrode. This has been studied with photosystem 1 (PSI) from Thermosynechococcus elongates.For efficient photocurrent generation a arther oriented immobilisation would be desirable which is complicated by the rather high molecular weight and the complex surface properties of PSI. In this context we have been focusing on the directional assembly of PSI on highly conductive graphene electrodes. In order to adjust the surface properties different aromatic molecules have been applied onto the graphene [1]. The different Π-systems serve as an artificial scaffold harbouring functional groups which interplay with the PSI. Particularly important is the hydrophilic-hydrophobic balance on the surface. In conclusion, an effective and rather directed assembly of PSI and a large photocurrent density has been obtained. It has to be mentioned here that photocurrent generation occurs already at open circuit potential with now additional driving force applied. Depending on the modifier used an unidirectional photocurrent generation can be achieved by this approach. Via the artificially modified graphene surface we have been able to create biohybrid systems with an improved photocurrent output. Here not only adsorption can be used for the functional assembly but also covalent linkage of PSI to the surface. A systematic investigation on the protein assembly and the resulting photoelectrochemical properties will be presented. For this quartz crystal microbalance experiments, chopped light voltammetry, constant potential measurements, photoaction spectra and experiments with methyl viologen have been performed. Moreover it can be demonstrated that the performance of such PSI electrodes can be further improved. Here nanoparticles are additionally coupled to the graphene-PSI system in order to enhance current generation under illumination. [1] S. C. Feifel, K. R. Stieger, H. Lokstein, H. Lux, F. Lisdat, Journal of Materials Chemistry A 3 (23) (2015) 12188-12196 [2] S. C. Feifel, H. Lokstein, M. Hejazi, A. Zouni, F. Lisdat, Langmuir 31 (38) (2015) 10590-10598