Electrochemistry concentration cells

Sanger and Grenbowe (75) combined the data from their earlier study with those of Garnett and Treagust, and compiled a list of students common misconceptions in electrochemistry. The list covered galvanic cells, electrolytic cells, and concentration cells. The role attributed to misleading or erroneous statements in textbooks as sources of misconceptions led these authors to analyze a number of general chemistry textbooks (75). 

In addition to the foregoing, it is customary to include under electrochemistry (I) processes for which the net reaction is physical transfer, e g., concentration cells (2) electrokinetic phenomena, e.g.. electrophoresis. eleclroosmnsis, and streaming potential (3) properties ot electrolytic solutions, if they are determined by electrochemical or other means, e g.. activity coefficients and hydrogen ion concentration (4) processes in which electrical energy is first converted to heal, which in turn causes a chemical reaction that would not occur spontaneously at ordinary temperature. The... 

Sanger, M.J., Greenbowe, T.J. Common students misconceptions in electrochemistry Galvanic, electrolytic and concentration cells. Journal Research of Science Teaching 34 (1997), 377... 

Basic equations for almost every subfield of electrochemistry from first principles, referring at all times to the soundest and most recent theories and results unusually useful as text or as reference. Covers coulometers and Faraday s Law, electrolytic conductance, the Debye-Hueckel method for the theoretical calculation of activity coefficients, concentration cells, standard electrode potentials, thermodynamic ionization constants, pH, potentiometric titrations, irreversible phenomena. Planck s equation, and much more, a indices. Appendix. 585-item bibliography. 197 figures. 94 tables, ii 4. 478pp. 5-% x 8. ... 

The final example, which also deals with aqueous solutions, gives a result that is commonly found in electrochemistry, when it is not possible to disregard the cell s ionic junction voltage. In this case, there is only one correct way of writing the equation, which involves mean activities as it should be. This applies to a particular type of cell that is sometimes called a concentration cell... 

A wet cell battery has a liquid electrolyte. It is also called as flooded cell, since the liquid covers all internal parts. Wet cells were a precursor to dry cells and are commonly used as a tool for electrochemistry. A particular type of wet cell known as a concentration cell is important in imderstanding corrosion. Wet cells may be primary or secondary cells. Some other primary wet cells are the Leclanche cell. Grove cell, Bunsen cell, chromic acid cell, etc. Wet cells are used in automobile batteries and telecommunication. 

Almost one hundred years after Volta s report of the voltaic cell, electrochemistry had become an essentially quantitative science. In the 1830 s Faraday had published his laws of electrolysis, and in the 1880 s Nernst (5) had developed a mathematical treatment of cell potentials with respect to ion concentration. 

PRINCIPLES AND APPLICATIONS OF ELECTROCHEMISTRY 5.5 Electrochemical concentration cells... 

In a similar way, electrochemistry may provide an atomic level control over the deposit, using electric potential (rather than temperature) to restrict deposition of elements. A surface electrochemical reaction limited in this manner is merely underpotential deposition (UPD see Sect. 4.3 for a detailed discussion). In ECALE, thin films of chemical compounds are formed, an atomic layer at a time, by using UPD, in a cycle thus, the formation of a binary compound involves the oxidative UPD of one element and the reductive UPD of another. The potential for the former should be negative of that used for the latter in order for the deposit to remain stable while the other component elements are being deposited. Practically, this sequential deposition is implemented by using a dual bath system or a flow cell, so as to alternately expose an electrode surface to different electrolytes. When conditions are well defined, the electrolytic layers are prone to grow two dimensionally rather than three dimensionally. ECALE requires the definition of precise experimental conditions, such as potentials, reactants, concentration, pH, charge-time, which are strictly dependent on the particular compound one wants to form, and the substrate as well. The problems with this technique are that the electrode is required to be rinsed after each UPD deposition, which may result in loss of potential control, deposit reproducibility problems, and waste of time and solution. Automated deposition systems have been developed as an attempt to overcome these problems. 

Sorensen is usually considered to be the first to have realized the importance of hydrogen ion concentration in cells and in the solutions in which the properties of cell components were to be studied. He is also credited with the introduction of the pH scale. Electrochemistry started at the end of the nineteenth century. By 1909, Sorensen had introduced a series of dyes whose color changes were related to the pH of the solution, which was determined by the H+ electrode. The dyes were salts of weak acids or weak bases. He also devised simple methods for preparing phosphate buffer solutions covering the pH range 6-8. Eventually buffers and indicators were provided covering virtually the whole pH range. 

Influence of PTFE content in the anode DL of a DMFC. Operating conditions 90°C cell temperature anode at ambient pressure cathode at 2 bar pressure methanol concentration of 2 mol dm methanol flow rate of 0.84 cm min. The air flow rate was not specified there was a parallel flow field for both sides. The anode catalyst layer had 13 wt% PTFE, Pt 20 wt%, Ru 10 wt% on Vulcan XC-73R carbon TGP-H-090 with 10 wt% PTFE as cathode DL. The cathode catalyst layer had 13 wt% PTFE, Pt 10 wt% on carbon catalyst with a loading 1 mg cm Pt black with 10 wt% Nafion. The membrane was a Nafion 117. (Reprinted from K. Scott et al. Journal of Applied Electrochemistry 28 (1998) 1389-1397. With permission from Springer.)... 

The final cell design, as in semi-infinite electrochemistry, depends very much on the goals of the experimenter. For example, when one is interested in single-electrode coulometry for n value, concentration, or spectral measurements, the cell requirements are minimal. Potential scan experiments (voltammetry, potential scan coulometry, steady-state voltammetry) or experiments... 

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