La pile à combustible microbienne, MFC, est un bioengine qui associe respectivement le principe biochimique et le principe électrochimique pour extraire les électrons stockés dans la matière organique et les transformer en électricité. Dans un MFC, des microbes électroactifs vivants, avec son système enzymatique complet, sont utilisés pour biocatalyser l'oxydation du combustible organique; une anode est introduite artificiellement pour détourner les électrons, ce qui a eu pour résultat le système respiratoire bactérien; et à l'opposé, une cathode entraîne le flux d'électrons qui est ensuite commuté sur le courant électrique. Les microbes électroactifs se répandent dans de nombreuses sources telles que le sol, le compost, les boues, les eaux usées, etc. Les aliments pour animaux, les combustibles organiques et / ou d'autres nutriments peuvent également être abondamment présents dans leurs sources matricielles et dans de nombreuses autres sources inestimables, couramment disponibles dans la vie quotidienne. L'abondance bactérienne et le carburant organique illimité sont les deux raisons attrayantes pour le développement d'une source d'énergie durable telle que le MFC, qui attire également notre attention dans cette recherche. Ici, nous avons développé MFC, double chambre (DCMFC) et chambre unique (SCMFC), alimentés par compost de jardin comme source électroactive et acétate de carburant. Pour des raisons de durabilité et d’autres avantages, c’est-à-dire praticables et respectueux de l’environnement, nous nous sommes principalement concentrés sur le SCMFC avec un système de cathodes respiratoires. La problématique commune du SCMFC est la production d’énergie limitée due principalement à la cinétique lente de la réaction de réduction de l’oxygène (ORR) dans la partie cathodique. Par conséquent, il est important de mettre au point le matériau de la cathode respiratoire qui présente une activité de catalyse appropriée vis-à-vis de la perte de réponse optique pour surmonter cette limitation. Le feutre de carbone (CF) est le matériau de support choisi qui convient à la fabrication de cathodes à respiration aérienne. Alors que le platine (Pt) et l’oxyde de manganèse (MnOx), respectivement, en tant que classe de catalyseur suprême et de second rang, ont été développés sur CF grâce à une méthode simple d’électrodéposition. Les matériaux résultants, dénommés ACF@Pt et ACF@MnOx, ont été caractérisés de manière complète par des méthodes électrochimiques et physicochimiques afin de déterminer leurs performances électrocatalytiques, supportant ainsi l’application de cathodes respiratoires. En conséquence, nous avons développé deux principaux types de cathodes respiratoires, à savoir ACF@Pt et ACF@MnOx, appliquées avec succès dans le SCMFC alimenté par du compost de jardin avec une densité de puissance respective de 140 mW m-2 et 110 mW m-2. De plus, les deux matériaux développés révèlent également des applications prometteuses. Par exemple, ACF@Pt a été utilisé comme anode de MFC, à la fois dans DCMFC et SCMFC, et a amélioré la densité de puissance jusqu'à 300 mW m-2. Fait intéressant, il est également montré comme un excellent électrocatalyseur dans la réaction de dégagement d’hydrogène, HER. Alors que le matériau ACF@MnOx présente un électrocatalyseur prometteur dans un système de type électro-Fenton à la minéralisation d'un matériau biréfractif, c'est-à-dire l'un des constituants polluants dangereux des eaux usées. / Microbial fuel cell, MFC, is a bioengine that combine biochemical and electrochemical principle respectively to extract the stored electrons in organic material and to turn them into electricity. In an MFC, living electroactive microbes, with its whole enzymatic system, are employed to biocatalyze the oxidation of organic fuel; an anode is artificially introduced to divert the electrons, as resulted in the bacterial respiratory system; and oppositely a cathode drives the electron flow that further be switched to electrical power. Electroactive microbes spread out in numerous sources such as soil, compost, sludge, waste water, and so on. The feed, organic fuel and/or other nutrient, also can abundantly be present in their matrix sources and in many other priceless sources, which commonly available in daily life. Bacterial abundance and unlimited organic fuel are the two attractive reasons for the development of sustainable energy source as such as MFC, which is also drawn our attention in this research. Herein, we developed MFC, double chamber (DCMFC) and single chamber (SCMFC), which powered by garden compost as electroactive source and acetate fuel. For sustainability reason and other advantages i.e. practicability and eco-friendly, we mainly focused on SCMFC with air-breathing cathode system. The common problematic of the SCMFC is the limited power production that mainly due to the slow kinetic of oxygen reduction reaction (ORR) in the cathodic part. Therefore, it is important to developed the material of air-breathing cathode which has a proper catalysis activity toward ORR to overcome this limitation. Carbon felt (CF) is the selected support material that suitable for air-breathing cathode fabrication. While, platinum (Pt) and manganese oxide (MnOx) respectively, as supreme and runner-up catalyst’s class, has been grown on CF through a simple electrodeposition method. The resulting materials, named as ACF@Pt and ACF@MnOx, have been characterized comprehensively by electrochemical and physicochemical methods to determine their electrocatalytic performances, which support for air-breathing cathode application. Accordingly, we have developed two main types of air-breathing cathode, i.e. ACF@Pt and ACF@MnOx, which have been successfully applied in SCMFC powered by garden compost with generated power density respectively 140 mW m-2 and 110 mW m-2. Moreover, the both developed material also reveal some promising application. For instance, ACF@Pt has been applied as MFC’s anode, both in DCMFC and SCMFC, and has improved the power density up to 300 mW m-2. Interestingly, it is also shown as an excellent electrocatalyst in hydrogen evolution reaction, HER. While, the ACF@MnOx material shows a promising electrocatalyst in an electro-Fenton like system to mineralization of biorefractory material i.e. one of the hazardous pollutant constituent of wastewater.

Electroactive microorganisms possess the unique capability to transfer catabolically generated electrons via extracellular electron transfer (EET) to solid electron acceptors beyond their cell membranes. Presumably, electroactive microorganisms have a considerable impact on natural redox processes and show potential for being harnessed in microbial electrochemical technologies (METs) providing novel solutions for environmental issues. Although many aspects of electroactive microorganisms and EET have been elucidated, the respective thermodynamics and the energy fluxes during growth are almost untapped. However, understanding thermodynamics is the key for realisticall assessing the influence of electroactive microorganisms on natural ecosystems and the feasibility of METs. Thus, the intention of the present thesis was to establish methods for analyzing the thermodynamics of electroactive microorganisms. This was achieved by developing the method bioelectrocalorimetry and a model framework for biofilm anodes. A bioelectrocalorimeter was used to measure the heat production of a Geobacter species dominated biofilm performing EET. By creating a heat flux balance, the microbial electrochemical Peltier heat was identified representing an entropic hurdle for EET reactions. The mathematical model for biofilm anodes comprises calculations of microbial growth thermodynamics and kinetics as well as physical, chemical, and electrochemical processes at different spatial and temporal scales. It demonstrates that more detailed experimental assessments of thermodynamic parameters of electroactive microorganisms are urgently required. Furthermore, the thesis at hand provides a comprehensive data set on the energy content of wastewater that can be used to evaluate the feasibility as well as the thermodynamic efficiencies of METs. In conclusion, the thesis provides tools and useful thermodynamic information for the establishment of a complete energy balance of electroactive microorganisms and the elucidation of the driving forces for EET.

Microbial resource mining of electroactive microorganism (EAM) is currently methodically hampered due to unavailable electrochemical screening tools. Here, we introduce an electrochemical microwell plate (ec-MP) composed of a 96 electrochemical deepwell plate and a recently developed 96-channel multipotentiostat. Using the ec-MP we investigated the electrochemical and metabolic properties of the EAM models Shewanella oneidensis and Geobacter sulfurreducens with acetate and lactate as electron donor combined with an individual genetic analysis of each well. Electrochemical cultivation of pure cultures achieved maximumcurrent densities (jmax) and coulombic efficiencies (CE) that were well in line with literature data. The co-cultivation of S. oneidensis and G. sulfurreducens led to an increased current density of jmax of 88.57 ± 14.04 μA cm−2 (lactate) and jmax of 99.36 ± 19.12 μA cm−2 (lactate and acetate). Further, a decreased time period of reaching jmax and biphasic current production was revealed and the microbial electrochemical performance could be linked to the shift in the relative abundance.