Electrospinning‐on‐Electrode Assembly for Air‐Cathodes in Microbial Fuel Cells

Abstract

to provide opportunities for the further improvement of life quality at a global level, and a drastic reduction of greenhouse gases emission. [1] In this scenario, the efforts devoted to the development of low-impact systems able to exploit renewable energy have increased continuously in the last years. Fuel cells technologies are expected to play a central role within the next future. Among them, microbial fuel cells (MFCs) offer a great potential for their ability to combine energy conversion to water treatment and monitoring, through the metabolic activity of exoelectrogenic microorganisms that directly oxidize organic matter, converting it into electrons. [2] Since energy production associated to MFCs is relatively low, one of the main targets of this research area has always been associated to the design of systems able to combine good efficiency to low fabrication costs. The use of oxygen as the final electron acceptor at the cathode has demonstrated to be a quite intriguing solution to design cheap and well behaving devices. [3] Good performance of air-cathode MFCs is strictly associated to the ability of efficiently running the oxygen reduction reaction (ORR) at the cathode. Since a catalyst is needed to reduce the high overpotential of the direct reaction pathway (ensuring four electrons for each O 2 molecule), interest is high in finding good options to substitute platinum. Indeed Pt is currently recognized as the reference catalyst for ORR but whose high cost limits the marketability of fuel cells. [4] Alternative materials must therefore be able not only to guarantee a behavior similar to Pt but also to reduce the costs for the electrode fabrication. Several works are available in the literature, discussing the use of catalysts alternative to Pt [5] for the ORR: platinum group metalfree catalysts, [6] carbon-based materials, [7] conductive polymers, [8] metal organic frameworks [9] and metal oxides [10] have been proposed. Among the latest, manganese oxides (Mn x O y ) are considered quite interesting candidates, since they combine low cost to electrochemical stability and optimal ORR activity. [11] However, further work is needed to integrate the catalysts into electrodes, possibly with an easy and not expensive A binder-free electrospinning-on-electrode (EoE) assembly is proposed for the decoration of nonflat electrodes with nanostructured catalysts. EoE assembly exploits the modulation of the electric field induced by conducting protrusions. Using nonflat electrodes as collectors, EoE assembly allows the arrangement of nanostructured catalyst with optimized electrochemical interfaces. This work discusses the decoration of carbon paper electrodes with nanostructured manganese oxide to catalyze the oxygen reduction reaction (ORR). Carbon fibers on top of carbon paper act as conductive protrusions, locally enhancing the electric field, and thus inducing a preferential arrangement of the electrospun. Two nanostructured Mn 3 O 4 are obtained by EoE assembly, i.e., nanofibers and nanobeads. The cat...

Electrospun Nanofibers: from Food to Energy by Engineered Electrodes in Microbial Fuel Cells

“…The duration of the electrospinning process was close to 10 min to ensure at the same time an ordered distribution of nanofibers, which were directly collected onto CP without a binder, and a high surface area-to-volume ratio. As demonstrated in our previous work [30], the ordered distribution is mainly due to the conductive protrusions of CP that induce electric field enhancement. This ordered distribution can be optimized when the thickness of the nanofibers is close to few micrometers.…”

“…Nanofibers mats based on PEO, were directly electrospun on a carbon-based material (named CP, Fuel Cell Earth, Woburn, Massachusetts, USA), used as reference material since it is the most employed anode in MFCs. As already demonstrated in our previous work [30], the morphology of CP, characterized by several conductive micro-protrusions, plays a crucial role in tuning a selective patterned deposition of PEO nanofibers (CP/PEO-NFs), thus leading to ensure a binder-free deposition of nanofibers. In particular, CP/PEO-NFs were obtained by electrospinning, starting from a polymeric solution containing PEO (purchased from Sigma Aldrich, with an average molecular weight Mw = 600 kDa) dissolved in deionized water.…”

“…During the last decades, some works in the literature [25][26][27] investigated the modification of carbon-based electrodes by the application of a polymeric matrix on their surfaces to increase the contact between bacteria and anodes in MFCs. Several polymeric matrices have been developed, using both natural polymers, such as agar, alginate, or agarose, and synthetic polymers [28][29][30]. Despite being interesting because of their sustainable origin and biocompatibility, natural polymers suffer from poor mechanical strength and durability, while synthetic polymers show an opposite behavior, since they combine higher mechanical strength and durability with a higher risk of toxicity for bacteria proliferation.…”

“…PEO-NFs were directly deposited onto CP-based electrodes, according to the electrospinning-onelectrode process, a binder-free method for nanofiber assembly onto an electrode that we introduced in our previous work [30].…”

“…The resulting anodes, named CP/PEO-NFs, were investigated in single-chamber MFCs (SCMFCs) and compared with reference devices using pure CP as anodes [30].…”