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Mixed Biotic and abiotic functionalysed electrodes for Plant Microbial Fuel Cells applications

Periodic Reporting for period 1 - HiBriCarbon (Mixed Biotic and abiotic functionalysed electrodes for Plant Microbial Fuel Cells applications)

Reporting period: 2018-09-03 to 2020-09-02

Microbial fuel cells (MFC) are promising electrochemical devices that can produce electricity generated by active microorganisms present in wastewater. The reactions at anode of MFCs can be catalysed by microbial biofilms capable of oxidizing organic matter (anode) whereas non-precious carbon soot-based powders are able to catalyze oxygen reduction (ORR) (cathode) producing electrical power from renewable resources. However, MFC power output to date remains low and often unpredictable due to the variability in activity achieved by the anodic microbial biofilms and from low catalytic properties of carbon soot-based powders at the cathode. Proper biofilm colonization at the anode and non-expensive catalyst at the cathode can allow the scale up of MFC and can introduce it as a real alternative green energy production, a Horizon2020 research priority, that is based on wastewater treatment process without external energy sources. Surface grafting with composites based on polyaniline/carbon allotropes demonstrates electron transfer promotion and better adhesion between biofilm and surface. Functionalization using aryldiazonium salts bearing a variety of functions can react under mild conditions via spontaneous or electrochemically assisted reactions from solution, yielding covalently attached moieties on carbons. This project developed a new approach towards MFC anodic catalysis though the introduction of surfaces that promoted the desirable bacteria recruitment through the grafting of aryl diazonium based saccharides. The MFC cathodic catalysis was performed with a porous structure obtained with commercial carbon templates and hydrothermal method to produce highly active catalytic centers without the use of precious metal (Platinum). To avoid cathodic catalyst degradation, the antifouling properties of 4-aminophenol-O-b-D-galactopyranosyl(14)-β-D-glucopyranoside (Lac) were explored by grafting the realized cathodic catalyst with a Lac coating. The performed tasks allowed to achieve the overall objective of the project: the realization of non-toxic protocol to address exoelectrogenic community over the MFC anodes and the production of durable and non-expensive cathodic catalyst to increase MFC power outputs with a totally ecofriendly approach.
HiBriCarbon project started with a) design and characterization of nitrogen doped carbon based materials for oxygen reduction reaction in neutral environment. Different nitrogen loadings on realized carbon scaffolds were obtained by varying the volume of introduced nitrogen during the deposition process followed by different annealing temperatures. Different treatments produced different electrochemical response towards Oxygen reduction reaction and the obtained electrochemical results demonstrated that the catalytic efficiency towards the reaction of interest is due to different active sites and scaffold properties at different pH of the tested solution. The modelled carbon scaffolds used during this research period allowed the understanding of catalytic oxygen reduction reaction mechanisms in neutral environment which is fundamental for Microbial Fuel Cell cathode optimization. B) Nitrogen incorporation into carbon based powders was obtained with nitric acid oxidation pretreatment followed by annealing under ammonia controlled flow over commercial powders: carbon black pearls 2000 and multiwalled carbon nanotubes. To further promote oxygen reduction reaction Iron acetate was introduced as active catalyst into the carbon matrix. Catalyst obtained with carbon black pearls 2000 showed comparable results with Platinum on Carbon based catalyst used as reference. C) Fouling and antifouling properties of 4-aminophenol-α-D-mannopyranose (Man) and 4-aminophenol-O-b-D-galactopyranosyl(1-->4)-β-D-glucopyranoside (Lac) respectively, were evaluated in microbial fuel cells anodes. Saccharides deposition was performed by optimizing deposition technique. The best deposition conditions were identified through, Electrochemical measurements, water contact angle measurements and atomic force microscopy imaging. Different types of deposited saccharides report differences in exoelectrogenic community response: MFCs equipped with grafted Man anodes showed 30% more faster startup time than MFC equipped with untreated anodes whereas slow startup response was obtained with Lac coated anodes. Lac coating strategy was employed as antifouling coating to prevent MFC cathode degradation. The antifouling properties of Lac were also explored with Quartz crystal Microbalance (QCM) showing antifouling effects as reported by low QCM frequency variations when Lac grafted electrodes are immersed in common wastewater. The obtained results were successfully published in high ranked specialized journals: Bioelectrochemistry, Carbon and Small. The fellow had the possibility to further disseminate his results in national and international conferences: ISE Satellite Student Regional Symposium on Electrochemistry, 37th Spring Meeting of the European Materials Research Society (E-MRS), 69th Annual ISE Meeting and 6th Mediterranean Young Researcher Days.
The work performed during this project allowed faster startup of Microbial Fuel Cells devices with reproducible power outputs. The work performed on cathodic reaction studies allowed the clarification of the different nitrogen species role at different pH solution as well as the scaffold metallic character contribution on the catalysis of interest by using both experimental and computational analyses. Following these results, the roles of graphitic nitrogen, pyridinic nitrogen and scaffold metallic character on the oxygen reduction reaction were then understood and we demonstrated that the influence of each of these variables is linked to the aqueous environment pH in which the catalyst is operating. The work performed on the anodic site linked the relation between surface hydrophilicity, saccharide structure and deposition protocol on the electroactive biofilm affinity. We studied the bioaffinity between two types of saccharides and exoelectrogenic biofilm and we developed an ecofriendly and non-expensive approach to reduce MFC startup delay of 30% with an increased reproducibility. Furthermore, HiBriCarbon project allowed the development of an antifoulant coverage that can be employed to prevent unwanted biofilm colonization and MFC components degradation. This approach is still based on non-expensive and non-toxic protocol as it is based on the same principle of the bio affine coatings with opposite result due to the different sugar chemistry. This will be beneficial for reducing MFC maintenance without further invasive techniques at unsustainable costs. HiBriCarbon project contributes to further understand the role of specific molecules on the electroactive biofilm affinity and it allowed the application of this protocol on a final working device. Furthermore, HiBriCarbon project allowed the production of performant, non toxic and economic non platinum based catalysts to produce energy at low costs. Both of the obtained achievements can be considered as next step for MFC commercialization in large scale. Furthermore, this will be beneficial to alternative renewable energy strategies that are becoming a priority due to climate change concerns: the studies performed in this work on anodic and cathodic reactions will help to decrease the existing reliance on fossil fuel-based electricity.