PhD Defence by Jitka Urbánková

Principal supervisor:

Professor Stephan Sylvest Keller

Co-supervisor:

Professor Jenny Emnéus

Co-supervisor:

Postdoc Galina Pankratova

Examiners:

Associate Professor Ada-Ioana Bunea, DTU Nanolab
Associate Professor Nicolas Plumeré, TUM
Associate Professor Emilia Peltola, UTU

Chairperson at defence:

Associate Professor Paul Kempen

Abstract:

Biophotovoltaics (BPVs) are devices utilizing the inherent capabilities of photosynthetic organisms, most commonly cyanobacteria and algae, for conversion of solar energy into electrical energy.

During illumination, photosynthetic organisms catalyze the split of water molecules in their photosynthetic apparatus into protons, oxygen, and electrons; these electrons then can participate in subsequent reactions of photosynthesis or can be harvested using an external electrode for electric current generation. Unlike other solar conversion systems, BPVs can also generate current in the dark due to cellular respiration, which also generates electrons. This photocatalytic water split is an extremely efficient reaction, with nearly 100% quantum efficiency under optimal conditions. However, the electron transfer from the photosynthetic organism to the electrodes is a highly inefficient process, notably limiting the electrical yield of BPV, leaving them far below their estimated potential.

The structure of the external electrode can notably influence the currents harvested from BPVs. This study explores pyrolytic carbon electrodes fabricated in cleanroom facilities of DTU Nanolab as a material suitable for BPVs with cyanobacteria Synechocystis sp. Furthermore, it investigates the possibility of the enhancement of the cyanobacteria/electrode interaction by introducing various micro and nanostructures in the surface of the electrode, which was achieved by the employment of various microfabrication methods. The biophotoanodes consisting of carbon electrodes with a layer of cyanobacteria placed in a water-based growth medium were tested for photocurrent production in custom setups developed for this purpose.

The measurements showed a significant increase in current production by introducing micro and nanostructures on the electrode surface compared to planar electrodes, which in most cases correlated with the electrode surface area increase of the electrodes related to the introduction of micro and nanostructures. However, a positive impact on the microorganism’s entrapment was also demonstrated.

This was further enhanced by order of magnitude by the introduction of an electron transfer mediator leveraging the electrons from the surface of the cyanobacteria to the electrode surface. Overall, the study provided a stable system for testing biophotoanodes for BPVs, proved pyrolytic carbon is a suitable material for this purpose, and demonstrated the positive impact of nano and micropatterning of the electrode surface on photocurrent production.