Pourbaix diagram

In electrochemistry, and more generally in solution chemistry, a Pourbaix diagram, also known as a potential/pH diagram, EH–pH diagram or a pE/pH diagram, is a plot of possible thermodynamically stable phases (i.e., at chemical equilibrium) of an aqueous electrochemical system. Boundaries (50 %/50 %) between the predominant chemical species (aqueous ions in solution, or solid phases) are represented by lines. As such a Pourbaix diagram can be read much like a standard phase diagram with a different set of axes. Similarly to phase diagrams, they do not allow for reaction rate or kinetic effects. Beside potential and pH, the equilibrium concentrations are also dependent upon, e.g., temperature, pressure, and concentration. Pourbaix diagrams are commonly given at room temperature, atmospheric pressure, and molar concentrations of 10−6 and changing any of these parameters will yield a different diagram. The diagrams are named after Marcel Pourbaix (1904–1998), the Russian-born Belgian ch

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CH-243: Electrochemistry of solutions

Les étudiants intègrent les notions de potentiels électriques, de niveau de Fermi de l'électron et appliquent l'équation de Nernst. Ils comprennent la conductivité ionique en solution et la distribution des charges sur une interface électrifiée. Les bases de l'ampérométrie sont présentées.

A selective chemiluminescence detection method for reactive oxygen species involved in oxygen reduction reaction on electrocatalytic materials

Pauline Bornoz, Christos Comninellis

An original selective and quantitative detection method for direct access to reactive oxygen species (ROS) generated in near-neutral aqueous solutions during transient electrochemical experiments is described herein. Several chemiluminescent probes, which were selected for their high selectivity toward ROS were used and the selective electrogenerated chemiluminescence (SECL) method was validated on several electrocatalytic materials known to exhibit different behaviors toward the oxygen reduction reaction (ORR); the examined electrodes consisted of platinum, Au(1 1 1), glassy carbon and boron-doped diamond (BDD). We first selected appropriate molecular probes that are suitable for use under electrochemical polarization conditions and that are chemiluminescent in the chosen aqueous solutions. The roles of the concentration, solubility and possible activation of the molecular probes were identified. Then, the information obtained by the simultaneous recording of the amperometric signal was correlated with the chemiluminescence intensity, which was measured with a highly sensitive photomultiplier tube (PMT). The experimental results were interpreted by constructing a potential vs. pH diagram for the oxygenated species. The complementary nature of the information about the mechanistic path of the ongoing mechanism of ORR on the different electrode materials allowed us to propose a unified scheme. A coupled proton electron transfer (CPET) mechanism can be invoked to explain the major differences observed from the identified reactive intermediates in relation to the electrocatalytic activity of the electrode materials. (c) 2013 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2013

Converse effect of pressure on the quadrupolar and magnetic transition in Ce3Pd20Si6

Julio Antonio Larrea Jiménez, Henrik Moodysson Rønnow

The heavy fermion compound Ce3Pd20Si6 displays unconventional quantum criticality as the lower of two consecutive phase transitions is fully suppressed by magnetic field. Here we report on the effects of pressure as an additional tuning parameter. Specific heat and electrical resistivity measurements reveal a converse effect of pressure on the two transitions, leading to the merging of both transitions at 6.2 kbars. The field-induced quantum criticality is robust under pressure tuning. We rationalize our findings within an extended version of the global phase diagram for antiferromagnetic heavy fermion quantum criticality.

Amer Physical Soc2016

Recovery of Cu, Pb, Cd and Zn from synthetic mixture by selective electrodeposition in chloride solution

Christos Comninellis

Secondary fly ash, resulting from thermal treatment processes, leads to a highly concd. chloride soln. with Cu, Pb, Cd and Zn as main heavy metals when dissolved in water. The selective electrodeposition of these heavy metals was studied. The goal was to recover, under potentiostatic conditions, each heavy metal with high purity, yield and reaction rates. By changing the parameters pH and overpotential, an optimum of the three requirements was looked for. In general, Cu, Pb and Cd could be sepd. with purities of 99 mol% or higher. Underpotential deposition probably is the main reason for the impurities in case of Cu and Pb deposition. H+ redn. as side reaction could be kept small for Cu, Pb and Cd even at lower pH by carefully selecting the overpotential. The quality of the deposits obtained depended strongly on the overpotential, but hardly on the pH. The deposits of Cu, Pb and Cd were easily removable from the cathode due to a dendritic growth mechanism. Zn deposits showed compact growth and adhered to the electrode surface. In addn., the structure of the deposits, revealed by scanning electron microscope (SEM), was compared with the current transients during electrodeposition. An enhancement factor r was introduced to compare the different deposition rates. [on SciFinder (R)]

2000

Electrochemistry

Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical ch

Iron

Iron is a chemical element with the symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common elem

Nernst equation

In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or full cell reaction) from the s