• Energy Research

The current scenario of energy storage and generation is demanding higher energy density supercapacitors. We need economic and green systems to adapt to the recent climate policies as well. Supercapacitors are eco-friendly energy storage devices with high power density and long-life cycle.1 There are mainly three different configuration of supercapacitor, symmetric, asymmetric, and hybrid based on the electrode material. Symmetric cells are constructed using identical materials in both electrodes. The performance of symmetric capacitor is limited by their small voltage window and lower energy density. Hybrid supercapacitors with asymmetric configuration are new alternatives with relatively high energy density compared to their symmetric counter parts. Generally, different materials are used in each electrode to design both the asymmetric cells or hybrid cells.2,3 Manganese oxide (MnO2) is a well-known electrode material for supercapacitor, due to its high theoretical capacitance (1370 F/g), stability in aqueous electrolyte, low toxicity and very low cost. Charging and discharging occurs mainly by fast surface redox reactions occurring in manganese oxide materials electrode with the help of cations (e.g. K+, H+, Na+). Apart from its good electrochemical behavior, MnO2 suffers from a low electronic conductivity and in a limited potential range. The performance of MnO2 electrodes might be enhanced by combining the oxide with electrically conductive carbon materials.4,5 Herein, we report the synthesis of MnO2 by a simple co-precipitation technique and its use as the positive electrode of the supercapacitor. Hybrid supercapacitors with asymmetric configuration has been constructed with a commercial activated carbon as negative electrode, MnO2 as positive electrode and Na+ exchange Aquivion membrane that has the dual function of separator and electrolyte. The hybrid cell exhibited well rectangular voltammograms at different scan rates and exhibiting high specific capacitance of 124 F/g at 0.2 A/g and energy density of 11 Wh kg-1. In addition, the type of hybrid supercapacitor was able to withstand harsh cycling by combining galvanostatic charging and discharging and floating conditions (i.e. 140 hours at 1.6 V) for up to 10,000 cycles without affecting the capacitance stability. Self-discharge studies on the cell were carried out, after 10000 charge discharge cycles. The cell was charged at 1.6 V for 3 h, then during the self-discharge, it retained more than 1 V up to 400 min. Further, the well EDLC behavior of the cell was improved by using a combination of MnO2 - carbon as positive electrode and activated carbon as negative electrode. Well rectangular cyclic voltammograms was exhibited for the fast charge discharge rates. The modified cell showed a high specific capacitance of about 100 F/g at 0.2 A/g. The synergistic effect of MnO2 and carbon resulted in a perfectly reversible charge storage redox processes, which occurs at the positive electrode. A detailed electrochemical study of these cells was carried out and compared with the symmetric carbon/carbon supercapacitor. A comprehensive analysis will be given during presentation.

Several carbon blacks and graphite were investigated as candidates for diffusion layer preparation in polymer electrolyte fuel cell electrodes (PEFC). Single cell electrochemical characterizations under different working cell conditions were carried out on the electrodes by varying the kind of carbon in the diffusion layer. An improvement in cell performance was found by using Shawinigan Acetylene Black (SAB) as carbon, resulting in a measured power density of about 360 mW cm(-2) in H-2/air operation at 70 degreesC and 1/1 bar. Pore size distribution and scanning electron microscopy analyses were carried out to help the understanding of the different behaviour of the investigated carbon diffusion layers.

The influence of Nafion content of PEFC gas diffusion electrodes with intermixed ionomer in the catalyst was evaluated. Electrochemical studies were carried out in a 50 cm2 single cell in H2/air operation at 70œC. Low platinum load (0.1 mg/cm2) electrodes with a Nafion content changing from 14 to 66 wt% were studied. The performance of PEFC electrodes is affected from the Nafion content and an optimal content of about 33 wt% of ionomer was found. Hg intrusion porosimetry and cyclic voltammetry were carried out to evaluate the pore size distribution and the electrochemical surface area, respectively. These data were correlated with single cell performance. The electrochemical experimental data were analysed using a theoretical equation and the obtained kinetics parameters were related to the catalytic layer structure.

Photo-supercapacitor (PSC) devices, which have the ability to convert solar energy into electricity and store it at the same time, are groundbreaking in the field of renewable energy. However, performing energy conversion and storage on the same system with an efficient and compact design is a very challenging task. In this work, novel graphitic carbon nitride (g-CN)/zinc oxide nanowire (ZnO NW) composites have been synthesized as photoactive electrode material. All-solid-state two-electrode PSC has been assembled by using the lithiated Nafion® membrane as the electrolyte and separator. Compared to the standard filter paper (FP) separator, the Li-form Nafion® membrane provided 5-times higher energy density under UV-illumination, at 1.5 V working potential and at 26.7 mAg current density. Moreover, g-CN/ZnO NW-based PSC having Li-form Nafion® membrane showed excellent cycling stability over 25,000 charge/discharge cycles with exceptional capacitance retention and Coulombic efficiency of 90.2 % and 99.9 %, respectively. In addition, UV illumination resulted in prolonged discharge time. In other words, energy density increased 21.5-fold with UV-illumination and reached 11 Wh kg at 1.5 V working voltage and 20 mAg current density.

The development of new membranes cheaper than Nafion®, with similar conductivity and lower hydrogen/methanol cross-over, is crucial for widespread commercial applications of Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) and Direct Methanol Fuel Cells (DMFCs) [1, 2]. This study reports on the synthesis and development of PEMs based on sulfonated polysulfone (sPSf) for application both in WEs and DMFCs at different operating temperatures. The sPSf was synthesized by using trimethyl silyl chlorosulfonate as sulfonating agent in a homogeneous phase of chloroform [3]. In order to try to reduce methanol crossover in DMFCs, functionalized silica was prepared (by reacting silica with neat chlorosulfonic acid at room temperature) and added as a filler in the sPSf membrane. The prepared membranes were physico-chemically characterized and used as electrolytes in PEMWEs and DMFCs [4, 5]. Besides, the transport properties of water and methanol through the electrolyte membranes as a function of methanol concentration (e.g. 1M - 5M CH3OH) and temperature (from room temperature up to 80°C) were analyzed by using Pulse Field Gradient (PFG) NMR technique. References [1] A. S. Aricò, S. Siracusano, N. Briguglio, V. Baglio, A. Di Blasi, V. Antonucci, J. Appl. Electrochem. 43 (2013) 107-118. [2] F. Lufrano, V. Baglio, P. Staiti, V. Antonucci, A.S. Aricò, J. Power Sources 243 (2013) 519-534. [3] F. Lufrano, V. Baglio, P. Staiti, A. Stassi, A.S. Aricò, V. Antonucci, J. Power Sources 195 (2010) 7727-7733. [4] S. Siracusano, V.Baglio, F.Lufrano, P.Staiti, A.S.Aricò, Journal of Membrane Science 448 (2013) 209-214. [5] F. Lufrano, V. Baglio, O. Di Blasi, P. Staiti, V. Antonucci, A. S. Aricò, Phys. Chem. Chem. Phys. 14 (2012) 2718-2726.

An electrochemical supercapacitor in all solid configuration using perfluorosulfonate ionomer as polymer electrolyte has been successfully realized. Electrodes of supercapacitor have been prepared using activated carbon material and Nafion ionomer. This latter had the double function of binder and electrolyte. Nafion 115 membrane has been used as electrolyte separator in the preparation of small scale supercapacitors. The capacitance performance of these devices is comparable or better than traditional systems, which use sulfuric acid as electrolyte. The electrochemical evaluation of studied supercapacitor has been carried out by cyclic voltammetry, dc charge/discharge measurements and electrochemical impedance spectroscopy. A capacitance of 90 F/g (referred to the weight of active carbon material in the electrode) has been obtained with carbon having surface area (SA) of about 1000m2/g and, a capacitance of 130 F/g with activated carbon having SA of 1500m2/g. These interesting results have been tentatively explained with an optimal configuration of electrodes and with the concomitant beneficial effects on the carbon pores of adsorbed water and Nafion distribution, which produce low distribute resistance in the carbon composite electrodes.