Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime.
DDE (2,2-bis (p-chlorophenyl)-1,1-dichloroetylene) is a very persistent and bioaccumulative pesticide and its residues are continuously found in the environment. Among the green remediation strategies for soil recovery, terrestrial Microbial Fuel Cells (MFC) are arousing great interest in scientific community. MFCs transform energy stored in the chemical bonds of organic compounds into electrical energy thanks to exo-electrogen microorganisms naturally occurring in soil, which catalyse oxidation and reduction reactions in the area between two graphite electrodes. This work reports preliminary data on the use of MFCs for promoting soil decontamination from DDE. Several experimental conditions (e.g. addition of compost and open/closed circuit) were applied for assessing how to improve MFC performance in favouring DDE removal. MFCs promoted a significant DDE removal (39%) after 2 months, while at the same time any pesticide decrease was observed in the batch condition. Compost addition stimulated microbial activity and improved MFC performance for a longer time.
Many soils contain a wide number of organic and inorganic chemicals and potential toxic elements due to industrial, agricultural and numerous anthropogenic activities. The recovery of polluted sites is an urgent need to be addressed and the development of innovative remediation technologies, which exploit nature-based solutions, is strongly encouraged, in line with the new EU Circular Economy Action Plan. Terrestrial microbial fuel cells (TMFCs) can be a valuable tool for recovering soils polluted by various organic and inorganic contaminants. TMFCs benefit from capabilities of microbial biofilms developed on the electrodes, which use the terminals as catalysts for metabolic activities, including contaminant degradation. This process produces energy, thanks to conversion of chemical bond energy (stored in the bonds of organic compounds) into electrical ones. This work describes construction materials, remediation capabilities and technology of the TMFCs, reporting the last advances in TMFCs such as soil-based reactors or in combination with plants (plant microbial fuel cell (PMFC)). Some aspects related to microbiological activities for pollutant biodegradation, plant-microbial interactions, energy production, and fields of application will be shown. Finally, abiotic factors which can improve bioremediation activities are also considered. Furthermore, limitations and issues for large-scale applications, as well as for stacking and scaling-up are discussed.
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