Vladimir S. Bagotsky

Electrochemical Power Sources: Batteries, Fuel Cells, and Supercapacitors

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Studies of Supercapacitor Carbon Electrodes with High Pseudocapacitance

During the last decades different new capacitor types were developed based on electrochemical processes. According to Conway [1] an electrochemical capacitor is a device in which different quasi-reversible electrochemical charging/discharging processes take place and for which the shape of the charging and discharging curves is almost linear, similarily to those in common electrostatic capacitors [1-13]. Electrochemical capacitors can be classified as film-type (dielectric), electrolytic and supercapacitors.

Experimental Methods for Investigation of Porous Materials and Powders

The best known method for investigating the porous structure of different materials is the method of mercury porosimetry MMP, which has some serious drawbacks. The method of standard contact porosimetry is based on the laws of capillary equilibrium. If two (or more) porous bodies partially filled with a wetting liquid are in capillary equilibrium, the values of the liquid’s capillary pressure p c in these bodies are equal. In this method the amount of a wetting liquid in the test sample is measured and compared with the amount of the same liquid in a standard sample with a known pore structure. Using different working liquids the wetting properties of the test sample can be determined.

Components of Power Sources/(or of Electrochemical Energetics)

The operation of a fuel cell involves the flow of different gaseous and liquid components in the membrane-electrode assembly (MEA). For a better understanding of the mechanism of all processes influencing the fuel cell efficiency, for mathematical modelling of these processes, and for a possibility of their optimization, a detailed knowledge of the geometrical structure and of the wetting (hydrophobic–hydrophilic) properties of the all components of the MEA is necessary. The porous structure and wetting properties of ten different carbonaceous support materials are described as well as the modification of this structure during different preparation stages of the catalytic layer, viz. the addition of the Nafion ionomer and the deposition of the platinum catalyst. The porous structure and wetting properties of different other fuel cell components (platinum catalyst on different supports, gas-diffusion layers, homogenous and heterogeneous membranes, etc.) are also described. As a result of structure optimization, it is possible not only to improve the electrical parameters (cell voltage at a given discharge current), but also to improve the stability of these parameters under conditions of changing flooding degrees (as a result of frequent changes of discharge current, temperature, and/or conditions of water removal). The operation of a fuel cell involves the flow of different gaseous and liquid components in the membrane-electrode assembly (MEA). Reactants must be supplied from the outside to the catalytic layer with a rate depending on the cell’s discharge current and the reaction products must be removed from this layer with an analogous rate. In low temperature fuel cells operating at temperatures below *120 C proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) in which polymer ion conducting membranes are used as electrolyte, water is present in gaseous state as well as in liquid state. A part of the pores in these fuel cells mainly formed by metallic catalyst particles have hydrophilic properties and are easily wetted by liquid water. Another part of the pores formed by Y. M. Volfkovich et al., Structural Properties of Porous Materials and Powders Used in Different Fields of Science and Technology, Engineering Materials and Processes, DOI: 10.1007/978-1-4471-6377-0_3, Springer-Verlag London 2014 19 carbonaceous particles and by some additives having hydrophobic properties remain dry during fuel cell operation and thus can be used for the transport of gaseous reagents. The operational reliability and durability of this type of fuel cells depend on a proper water management connected with the choice of predetermined flow directions for vapor and liquid water in the MEA pore network [1–3]. For a better understanding of the mechanism of all processes influencing the fuel cell efficiency, for mathematical modelling of these processes, and for a possibility of their optimization, a detailed knowledge of the geometrical structure and of the wetting (hydrophobic–hydrophilic) properties of the all components of the MEA is necessary. An investigation of the porous structure of ten different carbonaceous support materials is described as well as the modification of this structure during different preparation stages of the catalytic layer, viz. the addition of the Nafion ionomer and the deposition of the platinum catalyst. 3.1.1 The Catalytic Layer The catalytic layers of PEM fuel cell electrodes have a complex structure, which includes platinum particles deposited on carbonaceous supports, hydrophobic materials (PTFE), and an ionomer (mainly hydrated perfluorosulfonic acid introduced into the layer as a Nafion solution). The hydrophobic additive forms canals for the supply of the reacting gases (hydrogen and oxygen) to the catalyst’s surface and for evacuation of the reaction product (water vapor) from this surface. The ionomer provides ionic conductivity within the catalytic layer. Hydrophilic canals (mainly in the carbonaceous support) enable an even distribution of liquid water throughout the catalytic layer. The volume ratio of carbonaceous material and ionomer in the catalytic layers must be chosen so as to attain sufficient high values both for electronic and for ionic conductivities. The structural and wetting properties of the catalyst’s carbonaceous support particles influence to a great extent the properties of the catalytic layer and thus the efficiency of the fuel cell. A detailed study of these aspects began only recently. 3.1.1.1 The Porous Structure of the Catalytic Layer The method of standard contact porosimetry (MSCP) was used for investigation of an E-TEK catalytic layer with 40 % Pt on carbon black of the Vulcan XC-72 type and 5 % ionomer (from a Nafion solution in ethanol) [4]. This investigation was not systematic enough and did not include other types of catalyst supports. A detail investigation of the porous structure of ten different carbonaceous support materials was described as well as the modification of this structure during different preparation stages of the catalytic layer, viz. the addition of the Nafion ionomer and the deposition of the platinum catalyst [5]. The use of ten carbonaceous materials with different properties and different values of the specific surface 20 3 Components of Power Sources/(or of Electrochemical Energetics)

Characteristics and Structure of Powdered Medical Substances Used in the Pharmaceutical Industry

Medical substances (MS) used in the pharmaceutical technology are microheterogeneous solid-phase powder materials that underwent dispersion procedures in the gas phase. Many properties of these powders, particularly their stability and ability for subsequent processing into medications in forms acceptable to the consumer such as tablets, capsules, or suspensioms depend not only on their chemical composition, but also on their structure. MS have a high specific surface which results in increased inter-particle interactions and therefore to a great extent influences their chemical and technological properties. In order to optimize their further processing it is important to evaluate their structural properties by well-defined standard measuring procedures. In the pharmaceutical industry, besides MS different secondary, auxiliary substances are used which per se have no medical influence but help to produce the final medication. From the point of view of evaluating their structural properties these auxiliary substances are equivalent to the MS.

7. Molten Carbonate Fuel Cells

Molten carbonate fuel cells use carbonate salts of alkali metals as electrolyte. Due to the highly corrosive nature of the electrolyte, various countermeasures are being developed. MCFCs are expected for high-efficiency power generation systems using hydrocarbon fuels, such as natural gas and coal gas. This article describes the mechanisms of operation and cell degradation, as well as the features of MCFC systems.