China
Africa
Explore chapters and articles related to this topic
Micro and Nanopipettes for Electrochemical Imaging and Measurement
Published in Allen J. Bard, Michael V. Mirkin, Scanning Electrochemical Microscopy, 2022
Kristen Alanis, Sasha Elena Alden, Lane Allen Baker, Edappalil Satheesan Anupriya, Henry David Jetmore, Mei Shen
A compelling application of SICM is the ability to map local surface charge. When a charged surface is immersed in an electrolyte solution, fixed charges on the surface attract counterions near the surface/electrolyte interface to maintain electroneutrality, resulting in a charge balancing layer of ions in the solution. This is known as the electrical double layer (EDL) and the thickness (Debye length) strongly depends on the ionic strength of the electrolyte. Specifically, the Debye length is inversely proportional to ionic strength. For instance, monovalent electrolyte solutions with concentrations of 1 and 100 mM have Debye lengths of approximately 9, and 1 nm, respectively.265 The EDL can have a significant impact on nanoscale ion transport due to perturbation of the local ion concentration. A well-known phenomenon, ion current rectification (ICR), manifests when an unequal transference of cations and anions develops across a nanostructure due to preferential transport in one direction. ICR in pipettes was described by Bard et al. in quartz nanopipettes where the current-voltage (I-V) response deviated from linear ohmic behavior at a low electrolyte concentration.12 The current magnitude at one voltage polarity was larger compared to the opposite polarity.
A Physical and Chemical Equilibrium
Published in Danny D. Reible, Fundamentals of Environmental Engineering, 2017
In addition, the concentration of one or more of the other species may be specified by other reactions. In ground water systems, limestone (calcium carbonate, CaCO3) may control the concentration of the carbonate ion through the reaction () CaCO3⇔Ca+2+CO3−2As we shall see in the next section, the equilibrium in this reaction is governed by a solubility product constant, Ksp, which for CaCO3 is 4.57* 10−9 mol2/L2 at 25°C. Note that the presence of the additional ions affects the electroneutrality balance.
An Introduction to Conducting Polymer Actuators
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
Geoffrey M. Spinks, Philip G. Whitten, Gordon G. Wallace, Van-Tan Truong
The most important aspect of the electrochemical reaction for actuation in conducting polymers is the movement of anions (A−) into and out of the polymer [18,19]. The anions are necessary to balance the positively charged polymer chains that result from oxidation of the polymer. For electroneutrality, there must be equal numbers of positive and negative charges. The anion is sometimes called the dopant and the process of oxidation is sometimes called doping [20]. This terminology comes from inorganic semiconductors where the incorporation of small quantities of impurities greatly increases the conductivity. Oxidation of conducting polymers also greatly increases their conductivity, hence the analogy with semiconductor doping. Clearly, the movement of anions into and out of the polymer due to redox reactions causes dimensional expansion (swelling) and contraction (de-swelling). This redox reaction can be expressed by () P+(A−)(solid)⇄−e−(oxidized)+e−(reduced)P°(solid)+A−(liquid)
Dielectric properties of calcium-substituted lanthanum ferrite
Published in Journal of Asian Ceramic Societies, 2020
Refka Andoulsi-Fezei, Nasr Sdiri, Karima Horchani-Naifer, Mokhtar Férid
Apart from intrinsic oxygen vacancies, the lanthanum substitution would probably cause the formation of oxygen defects and iron ions in a tetravalent state. Indeed, to preserve electroneutrality, the substitution of a given cation by one with a lower valence can either decrease the number of oxygen anions, increase the transition metal oxidation state in the lattice, or both [41]. Based on the electroneutrality principle already cited, we summarize below a possible defect formation mechanism in La0.8Ca0.2FeO3-δ.