A sustainable and low-cost system, namely a photo-bioelectrochemical system (photo-BES), based on the natural blueprint of photosynthetic microorganisms was studied. The aim of this research work is to improve the efficiency of electron transfer of the microorganisms for bioelectricity generation. The first strategy adopted was the evaluation of the exoelectrogenic activity of oxygenic photosynthetic cyanobaterium, Synechococcus elongatus PCC 7942, in biophotovoltaic (BPV) platforms through a comparative performance analysis of bioanode materials. The second approach involved improving the performance of anoxygenic photosynthetic bacterium, Rhodopseudomonas palustris ATCC® 17001™, by varying the ratio of nitrogen to carbon sources (N:C) to maximise both biohydrogen production and exoelectrogenesis for conversion into bioelectricity in photosynthetic microbial fuel cells (photoMFCs). A linear correlation was obtained between average surface roughness/surface area and maximum power density of ITO-coated and graphene/ITO-coated substrates. Graphene/ITO-coated PET bioanodes produced the highest maximum power output of 29±4 μW m-2 in a single chamber BPV device due to improved biofilm formation and improved electrochemical activity. XG Leaf®, also known as graphene paper, helped to bridge the shortcomings of carbon fibres in terms of wettability. The most hydrophilic, 240 μm thick graphene paper, produced the highest maximum power output of 393±20 μW m-2 in a membrane electrode assembly (MEA)-type BPV device, mainly due to reduced electrochemical polarisation. A proof of concept study compared the performance of screen-printed graphene onto a membrane separator against 3D-printed bioanodes coated with carbon nanotubes. One mm thick 3D-printed bioanode was better performing as its structures promoted a much denser biofilm with extensive fibrous extracellular matrix. Using a ratio of N:C=0.20 resulted in higher biohydrogen production and higher exoelectrogenic activity, generating a maximum power output of 361±157 mW m-2 and 2.39±0.13 mW m-2, respectively. This study provided additional insight in improving the electron transfer efficiency, which could be used to further optimise photo-BESs as part of future research and development for sustainable technologies.

The aims of this project were to investigate a range of limitations affecting the electrical performance of bioelectrochemical systems (BES) and their use as analytical tools. The model cyanobacterium Synechocystis sp. PCC6803 was used to characterize light-driven BESs, or biophotovoltaic (BPV) devices. The phycobilisome (PBS) antenna size was altered to modify light absorption. At low to medium light intensities the optimum PBS antenna size was found to consist of one phycocyanin (PC) disc. Incorporating pulsed amplitude fluorescence (PAM) measurements into the BPV characterization allowed simultaneous comparison of photosynthetic efficiency to EET in Synechocystis. Non-photochemical quenching (NPQ) was investigated as a limiting factor in biophotovoltaic efficiency and was found to be reduced in the PBS antenna-truncated mutants. Fluorescence and electrochemical data were combined to develop a framework for quantifying the efficiency of light to bioelectricity conversion. This approach is a first step towards a more comprehensive and detailed set of analytical tools to monitor EET in direct relation to the underlying photosynthetic biology. A set of metabolic electron sinks were deleted to remove a selection of pathways that might compete with extracellular electron transfer (EET). The combined deletion of a bi-directional hydrogenase - HoxH, nitric oxide reductase - NorB, cytochrome-c oxidase - COX, bd-quinol oxidase - cyd, and the respiratory terminal oxidase - ARTO, roughly doubled light driven electron flux to EET. Deletion of nitrate reductase - NarB, and nitrite reductase - NirA, increased EET to a similar degree, but combination with the other knockouts compromised cell viability and did not increase output further. In addition to Synechocystis, the purple non-sulphur α-proteobacterium Rhodopseudomonas palustris CGA009 was used to test the effect of storage molecule synthesis knockout in a more industrially relevant organic carbon source driven BES, or microbial fuel cell (MFC). However, the removal of glycogen and poly-ß-hydroxybutyrate (PHB) did not have a significant effect on electrical output. Finally, the importance of electrode material and design for cell to anode connections in an MFC was investigated. EET from R. palustris was greatly enhanced using custom designed graphene and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) aerogels. Pristine graphene is also shown for the first time to be a viable, low cost alternative to platinum as a cathodic catalyst. Together, these results present a holistic view of major limitations on electrical output from BESs that may contribute to enhancing EET for power generation from MFCs in the long term, and optimization of BPV devices as reliable analytical tools in the short term.