The role and utilization of pseudocapacitance for energy storage by supercapacitors

We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochemical hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review standard experimental methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the number of electrically accessible active sites or increasing the turnover frequency of each site. Then we consider a number of state-of-the-art molybdenum sulfide catalysts, including crystalline MoS2, amorphous MoSx, and molecular cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnov...

Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide Nanomaterials

Electrochemical impedance spectroscopy has become a mature and well-understood technique. It is now possible to acquire, validate, and quantitatively interpret the experimental impedances. This chapter has been addressed to understanding the fundamental processes of diffusion and faradaic reaction at electrodes. However, the most difficult problem in EIS is modeling the electrode processes, which is where most of the problems and errors arise. There is an almost infinite variety of different reactions and interfaces that can be studied (corrosion, coatings, conducting polymers, batteries and fuel cells, semiconductors, electrocatalytic reactions, chemical reactions coupled with faradaic processes, etc.) and the main effort is now being applied to understanding and analyzing these processes. These applications will be the subject of a second review in a forthcoming volume in this series.

Electrochemical Impedance Spectroscopy and its Applications

AC and DC study of the temperature effect on mild steel corrosion in acid media in the presence of benzimidazole derivatives

The electrochemical desorption of n-alkanethiol monolayers from polycrystalline Au and Ag electrodes

Electrocrystallization: Nucleation and growth phenomena

An EIS study of aluminium barrier-type oxide films formed in different media

AC-impedance measurements on aluminium barrier type oxide films

A simplified physical model of inhomogeneous aluminum oxide layers, including the formation of passive and active pits is developed in order to explain experimental impedance data of technical samples prepared under different formation and sealing conditions. Moreover, aging and corrosion effects after long time exposure in different climate are studied and compared with model simulations and experiments under artificial corrosion conditions.

AC‐Impedance Measurements on Corroded Porous Aluminum Oxide Films

The two‐ and three‐dimensional nucleation and the metal ion adsorption process are discussed as initial steps for electrocrystallization on the same or on a foreign substrate. The metal ion adsorption takes place in the underpotential range, which is more positive than the equilibrium potential of the nucleated metal/metal ion electrode. Thermodynamic considerations show that an overlapping of disturbing processes in the underpotential range can be characterized by a factor , which is called charge‐coverage coefficient or electrosorption valency. It is a function of different independent variables. The metal monolayer model is satisfied only in the simplest case for (valency of metal ions in solution).The different experimental methods for determining the thermodynamics, kinetics, and structure of metal ion adsorbates are critically discussed. The most reliable thermodynamic results are obtained by the twin‐electrode thin‐layer technique. Kinetic data can be obtained by pulse measurements under potentiostatic‐galvanostatic conditions. The structure of metal films can be determined by combining different methods including optical investigations.Results are given for different systems. In the systems Au/Ag+ , Au/Tl+, and Au/Pb++ the metal monolayer model is practically valid. In the case of Cu++ ion adsorption on Au the redox reaction forming Cu+ ions acts as a disturbing process. A cosorption of anions takes place in the system Ag/Pb++. The formation of alloys in the underpotential range was observed in the systems Pt/Pb++ and Bi/Pb++.The structure of metal ion adsorbates must be in correlation with the nucleation phenomena at more negative potentials. In many systems no three‐dimensional nucleation overvoltage is observed by using a quasi‐steady‐state experimental technique. The density of the crystal imperfections and the crystallographic orientation of the surface planes influence the metal ion adsorption process and the structure of films. The results obtained in the systems Ag (poly‐ and monocrystalline)/Tl+ can be explained by assuming the formation of superlattices on the electrode surface.Kinetic investigations in the systems Au/Ag+, Au/Tl+, and Au/Pb++ show relatively high exchange current densities for the metal ion adsorption process. In these cases the experimental results can be explained by assuming surface diffusion of adions as the rate determining step in the adsorption process. In the system Au/Cu++, a charge transfer step is rate determining, which probably forms precedingly Cu+ ions.

W.J. Lorenz

Papers

Electrocrystallization: Nucleation and growth phenomena

An EIS study of aluminium barrier-type oxide films formed in different media

AC-impedance measurements on aluminium barrier type oxide films

AC‐Impedance Measurements on Corroded Porous Aluminum Oxide Films

The Formation of Monolayer Metal Films on Electrodes