Optimisation of a Pseudomonas aeruginosa microbial fuel cell coupled with additive manufacturing of graphene electrodes to enhance power outputs

Slate, Anthony Joseph (2019) Optimisation of a Pseudomonas aeruginosa microbial fuel cell coupled with additive manufacturing of graphene electrodes to enhance power outputs. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Due to the ever-increasing concern of climate change, research into alternative renewable energy generation is a priority. Microbial fuel cells (MFCs) offer one potential avenue to be explored as a partial solution towards combating the over-reliance on fossil fuel based electricity generation. Limitations such as low power generation, expensive electrode materials and the inability to scale up MFCs to industrially-relevant capacities have slowed MFC development. However, new electrode materials (e.g. graphene) coupled with a more thorough understanding of the mechanisms in which exoelectrogenic bacteria mediate electron transfer have the potential to dramatically increase MFC power outputs. The primary aim of this thesis was to optimise MFC power outputs by incorporating graphene in 3D-Printed electrodes. The MFC literature was reviewed in Chapter One. Graphene electrodes were optimised for electrochemical performance by varying individual lateral flake size of carbon paste electrodes (Chapter Two), a reduction in the individual lateral flake size of graphite and graphene electrodes enhanced electrochemical activity up to a specific size (ca. 2 µm). Graphene flakes smaller than this threshold exhibited no further improvement in electrochemical activity. A commercial filament was 3D-Printed to fabricate electrodes, 3D-Printed BM (Black Magic), which comprised of 8 wt.% graphene. These electrodes were evaluated for electrochemical performance, chemical composition (Raman spectroscopy) and surface properties (optical profilometry and physicochemistry). This included a novel quantification technique, which utilised the electrodeposition of molybdenum dioxide (MoO2) nanowires coupled with multifractal analysis, to deduce the electroactive areas of the electrodes (Chapter Three). The most exoelectrogenic Pseudomonas aeruginosa strain was selected using several key parameters for use within an MFC application (Chapter Four). Pseudomonas aeruginosa strain ATCC 9027 was selected, based on growth kinetic assays (cell viability), biofilm formation, pyocyanin production (via liquid chromatography-mass spectrometry) and hydrophobicity status, in conditions that were representative of the batch-fed MFC configuration (120 h; 37 °C; anaerobic; static). Alternative anaerobic growth conditions were explored, but there was no significant difference between P. aeruginosa cell proliferation in glucose or LB media and interestingly, no accumulation of pyocyanin was evident. XI Chapter Five combined the previously described 3D-Printed BM electrodes with bacterial selection and growth conditions in a MFC configuration. MFC cell potential was determined at 0 h, 24 h, 48 h, 72 h, 96 h and 120 h and power, power density, current and current density were calculated via Ohm’s law. Bacterial viability was determined for each time-period. The 3D-Printed BM electrodes demonstrated conductivity similar to that of the carbon cloth electrodes (the current benchmark in MFCs) in the presence of P. aeruginosa, in both anaerobic LB and glucose based media over a 120 h incubation period. The use of 3D-Printed BM electrodes had no significant detrimental effect on P. aeruginosa viability, but dramatically enhanced biofilm production. To visualise P. aeruginosa cells on the surface of each electrode and the cationic exchange membrane (CEM), confocal microscopy and scanning electron microscopy was conducted. Chapter Six provided a conclusion to this thesis, summarising the optimisation methods and MFC power outputs obtained. Overall, this study found no significant difference in power outputs from the 3DPrinted BM electrode and the carbon cloth electrode when tested in the same media with P. aeruginosa. Furthermore, the potential for future work is also detailed which could progress and translate this MFC research into industrially-relevant and applied areas.