Anti-corrosive siloxane coatings for improved long-term performance of supercapacitors with an aqueous electrolyte

This paper reports on the impact that the corrosion of the stainless steel current collectors has on the performance fade of a symmetric, carbon/carbon electrochemical capacitor, operating with an aqueous electrolyte (1M Na2SO4). The results obtained by applying electrochemical ageing protocols (voltage-holding tests) confirm that the current collector of the positive electrode undergoes tremendous degradation during 200 h in the charged state. To prevent the detrimental impact of the corrosion, a hydrophobic siloxane coating has been successfully applied. In the case of siloxane-protected current collectors that are subjected to identical ageing protocols, no significant deterioration in the electrochemical capacitor performance was observed. The siloxane coating reduces the electrochemical corrosion rate of 316L stainless steel significantly, as the potentiodynamic polarization tests and the electrochemical impedance spectroscopy results show. The presence of the coating is demonstrated by the water contact angle measurements, atomic force microscopy and energy-dispersive X-ray spectroscopy analysis

Saccharide-based graphitic carbon nanocoils as supports for PtRu nanoparticles for methanol electrooxidation

6 pages, 4 figures.-- Printed version published Sep 27, 2007.Highly graphitic carbon nanocoils were synthesised from the catalytic graphitization of carbon spherules obtained by the hydrothemal treatment of different saccharides (sucrose, glucose and starch). This nanostructured carbon was characterized by X-ray power diffraction, N2 adsorption and microscopy techniques (SEM and TEM). The carbon nanocoils were used as a support for PtRu nanoparticles, which were well-dispersed over the carbon surface. This catalytic system was investigated for use as an electrocatalyst for methanol electrooxidation in an acid medium. The experiments were carried out at two working temperatures (25°C and 60°C). It was found that the carbon nanocoils supporting PtRu nanoparticles exhibit a high catalytic activity, which is even higher than that of conventional carbon supports (Vulcan XC-72R). We believe that the high electrocatalytic activity of the carbon nanocoils presented here is due to the combination of a good electrical conductivity, derived from their graphitic structure, and a wide porosity that allows the diffusional resistances of reactants/products to be minimized.The financial support for this research work provided by the Spanish MCyT (MAT2005-00262) is gratefully acknowledged. MS acknowledges the assistance of the Spanish MCyT in awarding a FPU grant. G.A. acknowledges the financial support of the Polish grant DS 31-129/2007.Peer reviewe

Materials and mechanisms of electrochemical processes in lithium-sulfur cell

Lithium-sulfur (Li-S) cells are now attracting a lot of attention among battery scientists and engineers due to their potential for replace current Li-ion technologies as ta main energy storage chemistry. It is well known that Li-S cells operate according to a significantly different mechanisms as compared to Li-ion chemistries. In particular, upon discharge the sulfur species undergo a set of complex electrochemical transitions starting from elemental sulfur down to Li2S. In order to design a viable Li-S battery, it is of decisive importance to fully understand this complex electrochemistry that needs aprotic solvents to function. This article is concise a review of mechanisms and materials involved in state-of-the-art Li-S cells. Electrochemical processes have been described according to the latest state of research, as well as main types of cathode, anode and electrolyte materials and chemicals. Also, main scientific and technological challenges and obstacle in designing commercially viable Li-S batteries have been pointed out

Wpływ węglanu wapnia i jego modyfikacji na proces wytłaczania oraz wybrane właściwości użytkowe wylewanych folii polipropylenowych

The effect of unmodified and stearic acid-modified calcium carbonate (5, 10, 20 and 30 wt%) on selected properties (tensile strength, puncture resistance, haze and gloss) and processability of polypropylene films (MVR, extensional viscosity) was investigated. The composites were obtained in the twin-screw extrusion process with cold granulation, and the films in the single-screw extrusion process, using a flat die head (so-called cast films) and a chill roll type cooling and pull-back device. It has been shown that stearic acid is an effective modifier of polypropylene processing properties both under shear and tensile flow conditions (lower extensional viscosity of films containing modified calcium carbonate).Zbadano wpływ dodatku 5, 10, 20 oraz 30 % mas. niemodyfikowanego imodyfikowanego kwasem stearynowym węglanu wapnia na wybrane właściwości użytkowe (wytrzymałość na rozciąganie, odporność na przebicie, zamglenie, połysk) iprzetwórcze folii polipropylenowych (MVR, lepkość wzdłużna). Kompozyty otrzymano w procesie dwuślimakowego wytłaczania z granulacją na zimno, a folie w procesie jednoślimakowego wytłaczania, przy użyciu głowicy płaskiej (tzw. cast films) oraz urządzenia chłodząco - odciągającego typu chill roll. Wykazano, że kwas stearynowy jest efektywnym modyfikatorem właściwości przetwórczych folii polipropylenowych zarówno w warunkach przepływu ścinającego, jak i rozciągającego (mniejsza lepkość wzdłużna folii zawierających modyfikowany węglan wapnia)