Steric effects in adsorption of ions from mixed electrolytes into microporous carbon

With the goal to improve the capacitance in electrochemical double-layer capacitors (EDLCs) many studies on pore size/ion size relationship have been undertaken to achieve a better understanding of the charge storage mechanism in the electrochemical double-layer in confinement. A significant capacitance increase was achieved by using carbon electrodes with micropores (b1 nm), when the carbon pore size was close to the ion size. In this paper, the accessibility of narrow pores is investigated by selecting a carbon with a small pore size (b0.7 nm) and electrolyte mixtures with different ion sizes. It has been shown that the adsorption capacitance limitation observed for large cations and anions could be overcome by adding ions with a smaller effective size. This result demonstrates that the pores are accessible when their size matches the effective ion size and contradicts the surface saturation assumption; effective ion size which exceeds the pore size leads to current limitation. This work confirms that the steric effect is involved when ions are adsorbed into pores and highlights the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices

Evidence for electronic and ionic limitations at the origin of the second voltage plateau in nickel electrodes, as deduced from impedance spectroscopy measurements

The second plateau occurring during the reduction of the nickel oxyhydroxide electrode (NOE) was studied by impedance spectroscopy on a cell with a pasted electrode prepared from commercial undoped -Ni(OH)2. Measurements were performed at diverse states of reduction and a large variation of impedance upon the transition from the first to the second plateau was observed. This variation mainly takes place at low frequencies and is hence related to ionic diffusion. We observed that the impedance becomes more capacitive on the second plateau meaning that the proton diffusion is limited. These results would be consistent with the gradual formation of an insulating layer of nickel hydroxide at the interface between the NOE and the electrolyte upon reduction. Once this layer becomes compact the ionic diffusion would be hindered and forced to occur through this layer, which could explain the voltage drop observed

Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors

Microbatteries with dimensions of tens to hundreds of micrometers that are produced by common microfabrication techniques are poised to provide integration of power sources onto electronic devices, but they still suffer from poor cycle lifetime, as well as power and temperature range of operation issues that are alleviated with the use of supercapacitors. There have been a few reports on thin-film and other micro-supercapacitors, but they are either too thin to provide sufficient energy or the technology is not scalable. By etching supercapacitor electrodes into conductive titanium carbide substrates, we demonstrate that monolithic carbon films lead to a volumetric capacity exceeding that of micro- and macroscale supercapacitors reported thus far, by a factor of 2. This study also provides the framework for integration of high-performance micro-supercapacitors onto a variety of devices

Electrophoretic silica-coating process on a nano-structured copper electrode

A method for silica-coating at the nanoscale by electrophoretic deposition is presented here, using raw or grafted silica dispersions

Direct electrodeposition of aluminium nano-rods

Electrodeposition of aluminium within an alumina nano-structured template, for use as high surface area current collectors in Li-ion microbatteries, was investigated. The aluminium electrodeposition was carried out in the ionic liquid 1-ethyl-3-methylimidazolium chloride:aluminium chloride (1:2 ratio). First the aluminium electrodeposition process was confirmed by combined cyclic voltammetry and electrochemical quartz crystal microbalance measurements. Then, aluminium was electrodeposited under pulsed-potential conditions within ordered alumina membranes. A careful removal of the alumina template unveiled free standing arrays of aluminium nano-rods. The nano-columns shape and dimensions are directly related to the template dimensions. To our knowledge, this is the first time that direct electrodeposition of aluminium nano-pillars onto an aluminium substrate is reported

Electrodeposition of arrays of Ru, Pt, and PtRu Alloy 1D metallic nanostructures

Arrays of Ru, Pt, and PtRu one dimensional 1D nanowires NWs and nanotubes NTs were prepared by electrodeposition through the porous structure of an anodic aluminum oxide AAO membrane. In each case, micrometer-long NW and NT were formed with an outer diameter of ca. 200 nm, close to the interior diameter of the porous AAO membrane. Arrays of NW and NT can be formed by varying the metallic salt concentration, the applied potential, and the conductivity of the electrolyte. The Ru and Pt deposition rates were measured in the various deposition conditions, using an electrochemical quartz crystal microbalance. The mechanisms responsible for the formation of Ru and Pt NW and NT are discussed based on the observed deposition rates and models found in the literature. Finally, it is shown that arrays of PtRu alloy NT and NW can be readily prepared and their compositions can be varied over the whole compositional range by changing the metallic salt concentration of the electrodeposition bath

Del Ensanche a la ciudad actual: transformaciones en la idea de ciudad y en la forma de construirla: Pamplona desde 1915

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Microelectrode study of pore size, ion size, and solvent effects on the charge/discharge behavior of microporous carbons for electrical double-layer capacitors

The capacitive behavior of TiC-derived carbon powders in two different electrolytes, NEt4BF4 in acetonitrile AN and NEt4BF4 in propylene carbonate PC, was studied using the cavity microelectrode CME technique. Comparisons of the cyclic voltammograms recorded at 10–1000 mV/s enabled correlation between adsorbed ion sizes and pore sizes, which is important for understanding the electrochemical capacitive behavior of carbon electrodes for electrical double-layer capacitor applications. The CME technique also allows a fast selection of carbon electrodes with matching pore sizes different sizes are needed for the negative and positive electrodes for the respective electrolyte system. Comparison of electrochemical capacitive behavior of the same salt, NEt4BF4, in different solvents, PC and AN, has shown that different pore sizes are required for different solvents, because only partial desolvation of ions occurs during the double-layer charging. Squeezing partially solvated ions into subnanometer pores, which are close to the desolvated ion size, may lead to distortion of the shape of cyclic voltammograms

In situ NMR and electrochemical quartz crystal microbalance techniques reveal the structure of the electrical double layer in supercapacitors.

Supercapacitors store charge through the electrosorption of ions on microporous electrodes. Despite major efforts to understand this phenomenon, a molecular-level picture of the electrical double layer in working devices is still lacking as few techniques can selectively observe the ionic species at the electrode/electrolyte interface. Here, we use in situ NMR to directly quantify the populations of anionic and cationic species within a working microporous carbon supercapacitor electrode. Our results show that charge storage mechanisms are different for positively and negatively polarized electrodes for the electrolyte tetraethylphosphonium tetrafluoroborate in acetonitrile; for positive polarization charging proceeds by exchange of the cations for anions, whereas for negative polarization, cation adsorption dominates. In situ electrochemical quartz crystal microbalance measurements support the NMR results and indicate that adsorbed ions are only partially solvated. These results provide new molecular-level insight, with the methodology offering exciting possibilities for the study of pore/ion size, desolvation and other effects on charge storage in supercapacitors

Ámbitos y escalas en el urbanismo de Pamplona: de las “neighborhood units” a las unidades de ordenación

Pese a su descrédito en los términos en que habían sido formuladas, las comunidades, las unidades vecinales, siguieron estando presentes en el planeamiento. La sociología urbana, al menos, siguió ocupándose de ellas, sobre todo al definir los ámbitos de referencia de los equipamientos. El objeto de la investigación consiste en tratar de saber que fue de ellas después.Peer Reviewe