The aim of this work is to investigate the properties of biofilms, spontaneously grown on cathode electrodes of single-chamber microbial fuel cells, when used as catalysts for oxygen reduction ...reaction (ORR). To this purpose, a comparison between two sets of different carbon-based cathode electrodes is carried out. The first one (Pt-based biocathode) is based on the proliferation of the biofilm onto a Pt/C layer, leading thus to the creation of a biohybrid catalyst. The second set of electrodes (Pt-free biocathode) is based on a bare carbon-based material, on which biofilm grows and acts as the sole catalyst for ORR. Linear sweep voltammetry (LSV) characterization confirmed better performance when the biofilm is formed on both Pt-based and Pt-free cathodes, with respect to that obtained by biofilm-free cathodes. To analyze the properties of spontaneously grown cathodic biofilms on carbon-based electrodes, electrochemical impedance spectroscopy is employed. This study demonstrates that the highest power production is reached when aerobic biofilm acts as a catalyst for ORR in synergy with Pt in the biohybrid cathode.
This work discusses the design of highly stretchable, piezoresistive, flexible sensors obtained by electrospun nanofibers collected on rotating flexible wires. The resulting nanostructured sensors ...have a fiber-shape due to the inner plastic core being in intimate contact with the nanofibers forming the outer shell. The final fiber-shape thus facilitates the integration of the sensor into soft electronic platforms. Composite nanofibers, made of polyethylene oxide and multiwall carbon nanotubes, were selected as the sensitive material that is able to combine an effective response to mechanical deformation with compatibility in contact with the human body. Two flexible wire collectors were selected: a plastic wire and a plastic hollow wire. We demonstrate that the collectors induce a partially ordered distribution of NFs with good percolation behavior. Piezoresistive characterization confirmed the increase in the nanofibers’ electrical resistance with increasing applied pressure. The dimensionless sensitivity |∆R/R0| was calculated and plotted as a function of the applied pressure, demonstrating the good behavior of the new fiber-shaped pressure sensors.
Nanostructured semiconducting materials show intriguing properties not possessed by their macroscopic counterparts. First of all they exhibit high surface area to volume ratio, which offers ...interesting possibilities in several applications, as the improved and increased solar light adsorption in photoelectrochemistry and photocatalysis. Low charge–carrier mobility and high charge recombination rates are the key limiting factors in solar energy conversion systems. New extraordinary opportunities arise by the exploitation of nanomaterials. Indeed, learning to fine tune the behavior of nanoscale semiconductors and to integrate them in real devices have become one the main topics in the energy-related fields. Significant work has been especially done demonstrating that innovative photovoltaic architectures, and well-performing photoelectrochemical systems can be designed by the proper integration of nanostructured semiconducting metal oxides.
In this scenario nanofibers by electrospinning have attracted great interest, since they can be obtained by a relative simple and low-cost process, if compared to other technologies used for the fabrication of nanostructures. Moreover electrospinning offers several possibilities and strategies to design nanofiber-based nanostructures with different arrangement, well-controlled composition and morphology.
•A novel method to improve the sensitivity of piezoresistive in nanostructured electrically conductive polymer is developed.•Local dissolution induced by solvent droplets in electrospun composite ...nanofibers (NF) with multiwall carbon nanotube is an effective approach to design wearable sensors with improved performance.•Aerosol Mediated Localized Dissolution (AMLD) is effective in improving the 3D microporous NF mat by inducing local dissolution that improve the connections among fibers within the mat.•The effectiveness of applying an electrical potential difference during the AMLD process to improve the electrical connections among MWCNTs within the 3D microporous NF mat is proved.•Excellent piezoresistive response of the new flexible sensors is demonstrated in monitoring human joint motion.
This work proposes the use of solvents in the form of small size droplets to improve the connections among nanofibers (NFs) in electrospun composite nanofibers with carbon nanotube multiwalled (MWCNT) by improving the electrical and piezoresistive behavior of such electrically conductive polymer composites. The here proposed Aerosol Mediated Localized Dissolution (AMLD) process has been shown to be effective in improving the 3D microporous NF mat by inducing local dissolution that is effective in improving the connections among fibers within the mat. The AMLD process is demonstrated here for polyethylene oxide (PEO) / MWCNTs composite nanofibers, showing that the electrical conductivity is particularly improved in those samples with low content of MWCNTs, even below the original percolation threshold. The improved electrical conductivity is coupled with exceptional sensitivity of the flex sensor for low MWCNTs contents, this is particularly due to the ability of the AMLD process to preserve the high surface area of the 3D mat by inducing better fiber-to-fiber contacts in few regions only. In addition, this work demonstrates the effectiveness of applying an electrical potential difference during the AMLD process to improve the alignment of MWCNTs within the 3D microporous NF mat. The combination of voltage and AMLD allow to obtain a gauge factor as high as 571.9 with a MWCNTs loading of 1 wt%.
Display omitted
In the field of dye-sensitized solar cells, polymer electrolytes are among the most studied materials due to their ability to ensure both high efficiency and stability, the latter being a critical ...point of these devices. Hundreds of polymeric matrices have been proposed over the years, and their functionalization with several groups, the variation of their molecular weight and the tuning of the crosslinking degree have been investigated. However, the true effect that polymeric matrices have on the cell parameters has often been addressed superficially, and hundreds of papers justify the obtained results with a simple bibliographic reference to other systems (sometimes completely different). This work proposes a system of nanoscale growth and crosslinking of a polymer electrolyte inside a nanostructured photoanode. Electrochemical and photovoltaic parameters are carefully monitored as a function of thickness and degree of penetration of the electrolyte. The results derived from this study refute many clichés generally accepted and taken for granted in many literature articles, and – for the first time – a compromise between the amount of polymer, cell efficiency and stability is achieved.
The electric response to an external periodic voltage of small amplitude of dye-sensitized solar cells (DSCs) made up with an alternative architecture has been investigated. DSCs have been fabricated ...with a reversible sealing structure, based on microfluidic concepts, with a precise control on the geometric parameters of the active chamber. Cells with different electrolyte thicknesses have been characterized, without varying the thickness of the TiO2 layer, both under illumination and in dark conditions. Measurements of the electric impedance have been performed in the presence of an external bias ranging from 0 V to 0.8 V. The experimental data have been analyzed in terms of a transmission line model, with two transport channels. The results show that the photovoltaic performances of the microfluidic cell are comparable with those obtained in irreversibly sealed structures, actually demonstrating the reliability of the proposed device.
The present work proposes a versatile and efficient method to fabricate rubber nanofiber membranes with a controlled morphology and tailored functionality, based on the application of photoinduced ...thiol-ene cross-linking reactions to electrospun mats. Besides preventing the polymer cold flow and freezing the structure obtained by electrospinning, the photocuring step finely controls the morphology of the nanofiber mats, in terms of the fiber diameter up to the nanometer range and of the membrane porosity. Nanofiber membranes are also made chemically resistant, while retaining their flexibility. Finally, the proposed approach allows imparting specific functionalities to the rubber nanofibers: the type and concentration of the functional groups can be precisely tuned by changing process parameters (i.e., thiol/ene stoichiometric ratio and irradiation dose). Active chemical groups that remain available on the surface of the nanofibers can be used for further material modifications, as here proven by two target reactions. This key result is also demonstrated with electrospun membranes embedded into a microfluidic chip, opening the way to advanced functional flexible devices.
Overall performances of Single Chamber Microbial Fuel Cells (SCMFCs) with air-cathode are extremely improved by optimizing a cathodic catalyst not containing metals. To reach this goal, the main ...target is based on design nitrogen doped carbon-based nanofibers (N-CNFs) as catalyst layer at the cathode. The fine-tuning of the electrochemical properties of CNFs plays a key role to grant the direct oxygen reduction reaction (ORR). A pyrolysis treatment, conducted under inert atmosphere at 900 °C, is carried out to obtain a self-induced nitrogen doping in the carbon nanofibers during carbonization step, ensuring a proper value of electrical conductivity. The resulting N-CNFs, thanks to their content of nitrogen defects together with their high surface area, result to be a promising catalyst layer for the ORR. Physical, chemical and morphological properties of nanofibers are investigated, demonstrating the presence of N-doped graphitic sheets in the nanofiber mats. In particular, the key role of graphitic and pyridinic nitrogen related to the improvement of electrochemical behaviour of N-CNFs, is explained. All these features enhance the overall performance of SCMFCs. Indeed, SCMFCs with N-CNFs catalyst cathode reach a maximum power output comparable to that obtained by Pt based cathodes. The impressive result is strictly due to the important features of N-CNFs.
•Performance of SCMFCs can be drastically enhanced by using Nitrogen doped CNFs as catalyst layer.•N-CNFs are among the most promising catalyst layer at the cathode.•The optimized N-CNFs show good electrochemical behaviour toward oxygen reduction reaction.•SCMFC performance is comparable to the one of Pt/C catalyst layer.•The SCMFCs with N-CNFs as cathode achieve current densities of 7.6 ± 0.3 A g−1.
In this manuscript a near-room temperature crystallization process of anodic nanotubes from amorphous TiO2 to anatase phase with a fast 30 minutes treatment is reported for the first time. This ...method involves the exposure of as-grown TiO2 nanotubes to water vapor flow in ambient atmosphere. The water vapor-crystallized samples are deeply investigated in order to gain a whole understanding of their structural, physical and chemical properties. The photocatalytic activity of the converted material is tested by dye degradation experiment and the obtained performance confirms the highly promising properties of this low-temperature processed material.
PDF
