162,118 research outputs found
Regenerative fuel cells
No full textA regenerative fuel cell (RFC) is a hydrogen accumulator which is charged via an electrolyzer (electricity conversion into H2) and discharged via the fuel cell (H2 conversion into electricity), where the storage media is pressurized hydrogen. The also generated oxygen is mostly not stored in terrestrial applications. There are discrete RFCs (DRFC) consisting of two separate stacks (electrolyzer and fuel cell) and unitized RFCs (URFC) with one single stack working during charge in electrolysis mode and during discharge in fuel cell mode. URFCs show a high specific energy up to 1500 Wh kg−1. Furthermore, it is possible to optimize the power and energy of the system independently, which is important for seasonal storage of larger amounts of energy. In contrast to conventional electrochemical accumulators the discharge power of RFCs is unaffected by the state-of-charge of the system. But unfortunately, due to the long conversion chain with associated losses, RFCs generally have low levels of efficiency compared to conventional electrochemical accumulators. The high specific energy of URFCs makes the system interesting for niche applications in military and space areas where efficiency and related costs are not primary parameters. For civil terrestrial applications, however, costs and electrical efficiency are mostly primary parameters. DRFCs are preferred since the individual stacks (EL, FC) can be better optimized. However, for the time being, there are existing no commercial applications of RFCs, as they are not really competitive, especially not with electrochemical accumulators. In the future could be electricity storage with RFCs possible in off-grid or island applications in which a high level of autonomy is required but also in grid application with high share of renewables to stabilized power supply. In a broader sense are power-to-gas storage systems identically with DRFCs. Power-to-gas technologies and therefore also electrolyzers currently are developing strongly which will decreases the costs and increases the efficiency of RFC as well. The RFC technology is in the moment proton exchange membranes based, but they are relatively costly caused by use of platin group metal catalysts. Alkaline-RFCs could reduce the cost by using non-platin group metal catalysts. Because Alkaline-RFCs show an unsatisfactory performance and poor cyclability, therefore, the development is still in an initial stage. The efficiency of PEM-RFCs (URFC max. 35%, DRFC max. 40%) is relatively low. Higher efficiencies, however, show SO-RFCs. SO-URFCs already reach today in an early development state ca. 45% efficiency and could be used also in terrestrial applications
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
Cell Components – Electrodes | Nanoelectrodes
No full textThis chapter deals with the preparation, characterization, electrochemical behavior and application of arrays of nanoelectrodes
for electrochemical power sources. Different preparation methods are presented, focusing on membrane templated
deposition, seed-mediated growth and hydrothermal synthesis. Arrays of inlaid nanoelectrodes are preferred for advanced
electroanalytical and sensing purposes, where the Faradaic to capacitive current ratio need to be maximized, while complex
3D architectures are of particular interest for application requiring high specific surface and composed by high aspect ratio
nanomaterials, such as for batteries, supercapacitors and photoelectrochemical devices. The way how the morphology of the
array influences its electrochemical behavior is discussed, together with some fundamentals concerning the electrochemical
characterization. Finally, recent examples of studies on arrays of nanoelectrodes in batteries and supercapacitors are
presented
Electrochemical capacitors: Ionic Liquid Electrolytes
No full textDouble-layer carbon supercapacitors (electrochemical
double-layer capacitor (EDLCs)) based on two carbon
electrodes of high surface area separated by an electrolyte
are the most popular electrochemical supercapacitors. The
charge process is electrostatic with charge separation at
the two electrode–electrolyte interfaces. The EDLCs can
thus be modeled with two capacitances in series with what
is called equivalent series resistance (ESR). Given that the
electrode capacitance depends on the reciprocal of the
double-layer thickness, and that it is directly related to the carbon surface area, typically of several hundred square meters per gram of
carbon, the capacitance of EDLCs is significantly higher
than that of the dielectric and electrolytic capacitors. The
stored energy of EDLCs is also higher than that of the
dielectric and electrolytic capacitors, but it is lower than
that of batteries....
Murder on the mountain: author talk with Peter J. Wosh
No full textAuthor talk by Peter J. Wosh on May 5th, 2022, on his book, "Murder on the Mountain: crime, passion, and punishment in gilded age New Jersey.
Mr. Melvin J. Collier, RWWL AUC, June 2011
No full textThis video is a conversation with Mr. Melvin J. Collier. Mr. Collier talks about his book, "From Mississippi to Africa: A Journey of Discovery". Daniel Le, AUC Woodruff Library, is the interviewer
Hydrogen Evolution
No full textThe article begins with a brief presentation of the strategic importance of the hydrogen evolution reaction in various fields; this is followed by a discussion of its reversibility and of the factors on which reversibility depends. Adsorption of hydrogen atoms is a necessary step that depends on the interaction of metal surfaces with solvents. Thus, a correlation is found between M-H bond strength and hydrophilicity of metal surfaces. This point is discussed with the help of voltammetric curves for platinum-group metals. Besides being adsorbed, hydrogen atoms can also penetrate beneath the surface, thus affecting the adsorption energy on the surface. Hydrogen evolution is often accompanied by cathodic poisoning owing to the presence of metallic impurities. Ways to minimize this are discussed. The three most popular mechanisms of the electrode reaction for hydrogen liberation are discussed and kinetic parameters reported. The effect of the coverage of the electrode with the intermediate (H ad) is illustrated in detail. The effect of the nature of the electrode material (in electrocatalysis) is discussed using the so-called volcano curves depicting the dependence of the activity on M-H bond strength. A detailed analysis of electronic and geometric factors in electrocatalysis is also carried out. Finally, the findings of a survey of the most active materials in acidic and alkaline solutions are presented
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