Fritz Scholz

A new access to Gibbs energies of transfer of ions across liquid|liquid interfaces and a new method to study electrochemical processes at well-defined three-phase junctions

Abstract Droplets of polar and nonpolar aprotic solvents containing dissolved electroactive species can be easily attached to paraffin-impregnated graphite electrodes. When the electrode with the attached droplet is introduced into an aqueous electrolyte solution, the electrochemical reactions of the dissolved species can be elegantly studied. Provided the droplet does not contain a dissolved electrolyte, the electrochemical reaction will be confined to the very edge of the three-phase junction droplet|graphite|aqueous electrolyte. When a neutral species is oxidised, two pathways are possible: the oxidised species can remain in the droplet and anions will be transferred from the aqueous solution to the organic solvent, or the oxidised species may leave the droplet and enter the aqueous solution. Depending on the nature of the dissolved species, the nature of the organic solvent, the presence or absence of appropriate anions and cations in the two liquid phases, very different reaction pathways are possible. The new approach allows studies of ion transfer between immiscible solvents to be performed with a three-electrode potentiostat. Electrochemical determinations of the Gibbs energy of ion transfer between aqueous and nonpolar nonaqueous liquids are possible, whereas conventional ion transfer studies require the presence of a dissociated electrolyte in the organic phase. The new method considerably widens the spectrum of accessible ions.

Electroanalytical chemistry for the analysis of solids: Characterization and classification (IUPAC Technical Report)

Solid state electroanalytical chemistry (SSEAC) deals with studies of the processes, materials, and methods specifically aimed to obtain analytical information (quantitative elemental composition, phase composition, structure information, and reactivity) on solid materials by means of electrochemical methods. The electrochemical characterization of solids is not only crucial for electrochemical applications of materials (e.g., in batteries, fuel cells, corrosion protection, electrochemical machining, etc.) but it lends itself also for providing analytical information on the structure and chemical and mineralogical composition of solid materials of all kinds such as metals and alloys, various films, conducting polymers, and materials used in nanotechnology. The present report concerns the relationships between molecular electrochemistry (i.e., solution electrochemistry) and solid state electrochemistry as applied to analysis. Special attention is focused on a critical evaluation of the different types of analytical information that are accessible by SSEAC.

Electrochemical behaviour of solid lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) in an aqueous electrolyte system

Abstract Lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) were synthesized by self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. These transition metal oxides were mechanically immobilized on the surface of paraffin-impregnated graphite electrodes and their cyclic voltammetric behaviour in aqueous alkali electrolytes was examined. It was shown that both the oxides undergo proton insertion upon the reduction of Co3+ to Co2+ in LiCoO2 and Mn4+ to Mn3+ in LiMn2O4, while they deintercalate protons on the reverse oxidation. Scanning electron microscopy reveals spherical LiCoO2 particles with a very narrow size distribution. Energy dispersive X-ray detection proved the absence of metal cation intercalation.

Electrochemical Signals of Mitochondria: A New Probe of Their Membrane Properties†

techniques to probe their properties under (patho-)physiological conditions. The integrity of the mitochondrial membrane and changes in its composition play a crucial role in preventing or even triggering apoptosis. Here, we report that isolated functionally intact MI interact with the surface of a static mercury electrode in a way which is similar to the adhesion-spreading of liposomes [6–9] and thrombocytes, [10] that is, they attach to the hydrophobic mercury surface and disintegrate by forming islands of adsorbed molecules. This attachment is caused by the hydrophobic interaction between mercury and the lipid chains, [11] a topic with a long history and recently reviewed by Nelson. [12] This attachment is measurable because of the changes of double-layer capacity, which give rise to defined capacitive signals. The quantitative analysis of these signals allows the determination of the phase-transition temperature of the mitochondrial membrane, the determination of the size of MI, and indicates the physiological status of MI. Freshly isolated MI dispersed in a physiological KCl solution interact with the Hg surface giving capacitive current spikes which have a positive sign at negative potentials (Figure 1), and a negative sign at positive potentials versus the point of zero charge (pzc). The highest frequency of spikes was observed at � 0.9 V. This is very similar to the behavior of lecithin liposomes, indicating that the mitochondrial membrane also disintegrates on Hg and forms an island of adsorbed molecules. Counting the number of current spikes per time and surface area units allows analysis of the macrokinetics, that is, the number of disintegrations as a measure of the rate at which the MI interact with the Hg surface.

The Electrochemical Society

The work that A. Wilke and I put in to form the Electrochemical Society (Founded 22 April 1894, and renamed “Deutsche Bunsen-Gesellschaft fur Angewandte Physikalische Chemie” in 1902, it is now known as the “Deutsche Bunsen-Gesellschaft fur Physikalische Chemie”.), now known as the Bunsen Society, took place partly before and partly after 1895 when the discussion in Lubeck about energetics and my subsequent illness put a considerable discontinuity in my life. However, since the most important part took place before 1895 it seems most appropriate to deal with this now before going on to the new period which followed the move to the new institute and the conquest of a new research field—catalysis.

Identification of low-index crystal planes of polycrystalline gold on the basis of electrochemical oxide layer formation

AbstractThe electrochemical oxidation of single-crystal gold surfaces has been well studied, and the exposed crystal planes can be reliably distinguished based on the peak potentials of oxide formation. However, the multiple oxidation peaks of polycrystalline gold have not yet been unambiguously related to crystal planes. In this work, we used cyclic voltammetric responses of activated polycrystalline gold electrodes recorded in sulfuric acid solutions to allow constructing relationships between crystal planes and oxide peaks. The studies of oxide formation were complemented by measuring double-layer non-faradaic currents, lead underpotential deposition (Pb-upd), the oxygen reduction reaction (ORR), and the hydrogen evolution reaction (HER).n Graphical abstractThe link between three gold oxide current peaks and exposed low index crystal planes, viz. Au(100), Au(110) and Au(111) on polycrystalline gold electrode

First-order differential equations in chemistry

Many processes and phenomena in chemistry, and generally in sciences, can be described by first-order differential equations. These equations are the most important and most frequently used to describe natural laws. Although the math is the same in all cases, the student may not always easily realize the similarities because the relevant equations appear in different topics and contain different quantities and units. This text was written to present a unified view on various examples; all of them can be mathematically described by first-order differential equations. The following examples are discussed: the Bouguer–Lambert–Beer law in spectroscopy, time constants of sensors, chemical reaction kinetics, radioactive decay, relaxation in nuclear magnetic resonance, and the RC constant of an electrode.

Voltammetric techniques of analysis: the essentials

AbstractThis text is written for a course on instrumental methods of quantitative analysis. It summarizes the basic concepts of modern nvoltammetric techniques of analysis. The guiding concept of this text is to demonstrate how the ratio of faradaic to capacitive currents decides about the sensitivity of the techniques, and how this ratio can be increased by electronics, electrode construction and by chemical means. Finally, the advantages and disadvantages of voltammetric techniques of analysis are briefly described.

Oxygen electroreduction on polycrystalline gold electrodes and on gold nanoparticle-modified glassy carbon electrodes

The oxygen reduction reaction (ORR) in acid media can be catalyzed on gold electrodes when the surface is activated by mechanical or electrochemical pretreatments. The activation is caused by increased surface roughness and defects, or asperities. After activation, a slow recrystallization of the surface as a function of relaxation time leads to deactivation of the surface for the ORR. After removal of active centers, the surface is not affected over time, which reveals that the surface recrystallization is associated with the deactivation. Experiments using various amounts of Au nanoparticles (AuNPs) immobilized on glassy carbon (GC) show a positive shift of peak potential of oxygen reduction and peroxide oxidation with increasing particle coverage.

Acid-Base Diagrams

The math behind the pH-logci diagrams.- Constructing pH-logci diagrams.- The application of pH-logci diagrams for graphical estimation of the pH of solutions and for the derivation of simplified equations.- The use of pH-logci diagrams for the construction of titration diagrams.- Titration errors.