Shimshon Gottesfeld

Bio: Shimshon Gottesfeld is an academic researcher from University of Delaware. The author has contributed to research in topics: Membrane & Anode. The author has an hindex of 52, co-authored 113 publications receiving 19813 citations. Previous affiliations of Shimshon Gottesfeld include Los Alamos National Laboratory.

A printed circuit board approach to measuring current distribution in a fuel cell

Abstract: A new method of measuring current distribution in a polymer electrolyte fuel cell of active area 100cm2 has been demonstrated, using a printed circuit board (PCB) technology to segment the current collector and flow field. The PCB technique was demonstrated to be an effective approach to fabricating a segmented electrode and provide a useful tool for analysing cell performance at different reactant gas flow rates and humidification strategies. In this initial chapter of work with the segmented cell, we describe measured effects on current distribution of cathode and anode gas stream humidification levels in a hydrogen/air cell, utilizing a NafionTM 117 membrane and single serpentine channel flow fields, and operating at relatively high gas flow rates. Effects of the stoichiometric flow of air are also shown. A clear trend is seen, apparently typical for a thick ionomeric membrane, of lowering in membrane resistance down the flow channel, bringing about the highest local current density near the air outlet. This trend is reversed at low stoichiometric flows of air. At an air flow rate less than three times stoichiometry, the local performance starts to drop significantly from inlet to outlet, as local oxygen concentration drop overshadows the lowering in resistance along the direction of flow.

Effect of Ammonia as Potential Fuel Impurity on Proton Exchange Membrane Fuel Cell Performance

Abstract: Effects of NH 3 on proton exchange membrane fuel cell performance are reported. Traces of NH 3 in the anode feedstream cause a decrease in cell current. The extent of the effect depends on NH 3 concentration and time of exposure of the anode to NH 3 . High trace levels and long time of exposure result in severe and irreversible disability. We discuss possible mechanisms by which NH 3 affects cell performance. A method for trapping ammonia from contaminated fuel streams using a H + form ion exchange resin is presented.

Oxygen Reduction Kinetics on a Platinum RDE Coated with a Recast Nafion Film

Abstract: Measurements of currents of the oxygen reduction reaction (ORR) at a Pt RDE coated with a recast Nafion film yield the permeability of O/sub 2/ through such films. Combined with results from linear potential scanning experiments on similar electrodes, these measurements also allow the separate evaluation of the concentration of O/sub 2/ and its diffusion coefficient in such films. Similar recast Nafion films have been used successfully to promote protonic access to catalyst sites in fuel cells. Accordingly, the maximum film thickness which would allow adequate oxygen flux through such a layer is evaluated. Measurements in 85% H/sub 3/PO/sub 4/ at room temperature show that a very significant enrichment of O/sub 2/ (e.g., by a factor of 20) in a region close to the electrode can be achieved by coating the electrode with a recast Nafion film. This result is expected from the high solubility of O/sub 2/ in Nafion.

Oxygen Reduction at Pt0.65Cr0.35, Pt0.2Cr0.8 and Roughened Platinum

Abstract: Oxygen reduction in has been investigated at , and at surfaces produced from them by selective dissolution of the Cr component. Rotating disk electrodes (RDE) were used to examine the oxygen reduction reaction (ORR). The published (1–2) surface analysis using x‐ray photoelectron spectroscopy (XPS) combined with sputter profiling and Rutherford backscattering spectrometry (RBS) convincingly demonstrated that the surface region can be selectively depleted of the Cr component by electrochemical excursions to potentials positive of ~+1.25V vs. RHE. For the more Cr‐rich alloy very severe depletion (>500A) occurs upon prolonged potential excursions above +1.25V. For the sample, the surface depletion extends about 2–3 monolayers into the surface. Electrochemical characterization by cyclic voltammetry also confirms that the surface becomes progressively roughened as the potential exceeds the region where chromium is passive. Extensive roughening of the surface results in a significant increase of the measured ORR current per geometric area of the RDE. Tafel slopes of the ORR for moderately rough surfaces (roughness factor, ), produced from either starting alloy, are nearly identical to pure smooth Pt. For rougher surfaces (produced only at the more Cr‐rich starting alloy) the Tafel slopes determined from a mass‐transfer corrected plot of are also nearly identical to those obtained at smooth Pt. It is concluded that the measured increase of ORR current following the roughening of the RDE alloy electrode is due solely to the increase of Pt surface area. The mechanistic and practical implications of this effect in fuel cell electrochemistry are discussed.

Materials for electrochemical capacitors

Abstract: Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

A review of electrode materials for electrochemical supercapacitors

Abstract: In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

Materials for fuel-cell technologies

Abstract: Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Carbon-based Supercapacitors Produced by Activation of Graphene

Abstract: Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.