Electrochemical Performance of Symmetric Solid-State Supercapacitors Based on Carbon Xerogel Electrodes and Solid Polymer Electrolytes.

For the development and optimization of solid-state symmetrical supercapacitors, herein, we propose using carbon-based electrodes and sodium- and lithium-form Aquivion electrolyte membranes, which serve as the separator and electrolyte. Carbon xerogels, synthesized using microwave-assisted sol-gel methodology, with designed and controlled properties were obtained as electrode materials. Commercial activated carbon (YP-50F, "Kuraray Europe" GmbH) was used as the active material for comparison. Notably, the developed solid-state symmetrical supercapacitors provide sufficiently high specific capacitances of 105-110 F g-1 at 0.2 A g-1, along with an energy density of 4.5 Wh kg-1 at 300 W kg-1, and a voltage window of 0-1.2 V in aqueous environments, also demonstrating an excellent cycling stability for up to 10,000 charge/discharge cycles. These results can demonstrate the potential applications of carbon xerogel as the active electrode material and cation exchange membrane as the electrolyte in the development of solid-state supercapacitor devices.

New Insights into Properties of Methanol Transport in Sulfonated Polysulfone Composite Membranes for Direct Methanol Fuel Cells.

Methanol crossover through a polymer electrolyte membrane has numerous negative effects on direct methanol fuel cells (DMFCs) because it decreases the cell voltage due to a mixed potential (occurrence of both oxygen reduction and methanol oxidation reactions) at the cathode, lowers the overall fuel utilization and contributes to long-term membrane degradation. In this work, an investigation of methanol transport properties of composite membranes based on sulfonated polysulfone (sPSf) and modified silica filler is carried out using the PFG-NMR technique, mainly focusing on high methanol concentration (i.e., 5 M). The influence of methanol crossover on the performance of DMFCs equipped with low-cost sPSf-based membranes operating with 5 M methanol solution at the anode is studied, with particular emphasis on the composite membrane approach. Using a surface-modified-silica filler into composite membranes based on sPSf allows reducing methanol cross-over of 50% compared with the pristine membrane, making it a good candidate to be used as polymer electrolyte for high energy DMFCs.

Selectivity of Direct Methanol Fuel Cell Membranes.

Sulfonic acid-functionalized polymer electrolyte membranes alternative to Nafion(®) were developed. These were hydrocarbon systems, such as blend sulfonated polyetheretherketone (s-PEEK), new generation perfluorosulfonic acid (PFSA) systems, and composite zirconium phosphate-PFSA polymers. The membranes varied in terms of composition, equivalent weight, thickness, and filler and were investigated with regard to their methanol permeation characteristics and proton conductivity for application in direct methanol fuel cells. The behavior of the membrane electrode assemblies (MEA) was investigated in fuel cell with the aim to individuate a correlation between membrane characteristics and their performance in a direct methanol fuel cell (DMFC). The power density of the DMFC at 60 °C increased according to a square root-like function of the membrane selectivity. This was defined as the reciprocal of the product between area specific resistance and crossover. The power density achieved at 60 °C for the most promising s-PEEK-based membrane-electrode assembly (MEA) was higher than the benchmark Nafion(®) 115-based MEA (77 mW·cm(-2) vs. 64 mW·cm(-2)). This result was due to a lower methanol crossover (47 mA·cm(-2) equivalent current density for s-PEEK vs. 120 mA·cm(-2) for Nafion(®) 115 at 60 °C as recorded at OCV with 2 M methanol) and a suitable area specific resistance (0.15 Ohm cm² for s-PEEK vs. 0.22 Ohm cm² for Nafion(®) 115).