Electrodes transmission cells

A number of designs of transmission in situ XAS cells have been published for the study of bound catalyst electrodes.These cells all utilize a thin-layer geometry to minimize the contribution to the absorbance by electrolyte solution. The cell design reported by McBreen and co-workers shown in Figure 9 uses three layers of filter paper soaked in the electrolyte as a separator, or later a Nafion membrane between the working electrode and a Grafoil counter electrode. Bubbles in the electrolyte, that would result in noise in the XAS data, are... 

Figure 17.10 Gas-tight transmission cell for IR spectroelectrochemistry in moderate-melting salts (A) optically transparent electrode (OTE) port, (B) reference electrode and auxiliary electrode ports, (C) Si windows, (D) vacuum valve, (E) light path. [From P. A. Flowers and G. Mamantov, J. Electrochem. Soc. 136 2944 (1989), with permission.]...

Figure 3 Spectroelectrochemical cell configurations (1) transmission cell with optically transparent electrode (OTE) (2) transmission optically transparent thin layer electrode cell (OTTLE) with OTE (3) sandwich OTTLE cell with minigrid or reticulated carbon (RVC) electrode (4) long optical path-length cell (LOPTC) with light parallel to electrode surface (5) double transmission reflection cell (6) internal...

Transmission Cells Using Optically Transparent or Perforated Electrodes... 

Relative to the transmission cells described in Section 1.3, external reflectance cells are less simple to construct and require additional optics for incorporation into the optical path of the spectrometer. The advantages associated with the approach relate to the well-defined nature of the working electrode, the wider range of materials suitable for this purpose, and the greater control over the thickness of the thin layer of solution. These factors contribute to a much faster (>10x) rate of electrosynthesis for external reflectance compared to transmission cells. 

Figure 8 shows the transmission cell employed by O Grady and co-workers in the study of the nickel oxide electrode. Heineman and co-workers have employed a cell with reticulated vitreous carbon as an electrode material in x-ray spectroelectrochemical studies of various transition metal complexes. 

These coated glasses can be used as working electrodes [optically transparent electrodes (OTE)] in standard three-electrode arrangements provided that both glass and coating are chemically and electrochemically stable and inert in the used electrolyte solution and the applied range of electrode potentials. The use of a modified infrared spectroscopy transmission cell equipped with quartz windows for UV-Vis spectroelectrochemistry has been described [18]. Platinum layers deposited onto the quartz served as an optically transparent working electrode and an additional platinum layer served as a pseudo-reference electrode. A counter electrode outside the thin layer zone (in one of the tubes used for solution supply) served as a counter... 

Unlike a transmission cell that samples both the solution and the electrode surface, the LOPTLC configuration allows the separation of surface and solution processes (indeed a cell that could be used in both transmission and LOPTLC modes simultaneously might be very interesting). For example, irreversible adsorption processes may be studied [78] using a double logarithmic method. Three experimental cases were... 

Structural information on electrodes can also be obtained as a function of potential by X-ray using monochromatic synchrotron radiation and similar transmission cells to those used for XAS (Figure 7B). Transmission cells (Laue mode) are best suited to adsorbates, while reflection (Bragg) cells are used for thicker films. Laboratory rotating anode sources can also be used, and here the instrument usually demands a reflection cell geometry. Stable systems such as solid-state cells and batteries give better... 

In conclusion, SW-CAM allows us to accurately test the properties of capacitive porous carbon electrodes and calculate the electrode capacity and the various contributions to the observed resistance. In this case, the linear (external) resistance determines the total resistance and analysis suggests that we can assign this resistance to the external electrical circuit, while we can also tentatively conclude that the distributed (volumetric) resistance within the electrode may be close to the ideal value based on an ion transport resistance only determined by the free solution ion diffusion coefficients. This finalizes our exposition of the derivation of the various constants in the transmission line theory based on the SW-CAM technique. In conclusion, the SW-CAM technique is a robust, precise, and very informative method to perform EC analysis on two-electrode capacitive cells in aqueous solutions. 

Figure 1 Schematic diagram of spectroelectrochemical techniques at an optically transparent electrode (OTE). (A) Transmission spectroelectrochemistry (B) transmission spectro-electrochemistry with an optically transparent thin-layer electrode (OTTLE) cell (C) internal reflection spectroscopy (IRS). Reprinted by courtesy of Marcel Dekker, Inc. from Heineman WR, Hawkridge FM and Blount HN (1984) Spectroelectrochemistry at optically transparent electrodes. II. Electrodes under thin-layer and semi-infinite diffusion conditions and indirect coulometric titrations. In Bard AJ (ed) Electroanalytical Chemistry. A Series of Advances, Vol 13, pp 1-113. New York Marcel-Dekker.

Microwave power and its effect on the electrode/electrolyte interface, 439 Microwave region, Hall experiments, 453 Microwave spectroscopy, intensity modulated photo currents, 508 Microwave transients for nano crystalline desensitized cells, 514 Microwave transmission, as a function of magnetic field, 515 Minority carriers... 

The most extensive study of the nickel oxide electrode is that of McBreen et a/.,83 who employed an in situ cell in a transmission mode (see cell in Fig. 17). The study of nickel oxide is complicated by the numerous species present and their interconversion. McBreen... 

Figure 17. In situ transmission EXAFS cell for the study of Ni oxide electrodes. (From Ref. 83, with permission.)...

Applying a voltage to a pixel within the cell causes the molecules to move, aligning themselves parallel with the electric field imparted by the electrodes. This realignment destroys the helical structure, precluding the unhindered transmission of light, and the display appears black. 

The experimental techniques described above of charge—discharge and impedance are nondestructive. Tear-down analysis or disassembly of spent cells and an examination of the various components using experimental techniques such as Raman microscopy, atomic force microscopy, NMR spectroscopy, transmission electron microscopy, XAS, and the like can be carried out on materials-spent battery electrodes to better understand the phenomena that lead to degradation during use. These techniques provide diagnostic techniques that identify materials properties and materials interactions that limit lifetime, performance, and thermal stabiity. The accelerated rate calorimeter finds use in identifying safety-related situations that lead to thermal runaway and destruction of the battery. 

Collection of in situ XAS data using a single cell fuel cell avoids problems associated with bubble formation found in liquid electrolytes as well as questions regarding the influence of adsorption of ions from the supporting electrolyte. However, the in situ study of membrane electrode assemblies (MEAs) in a fuel cell environment using transmission... 

For in situ x-ray diffraction measurements, the basic construction of an electrochemical cell is a cell-type enclosure of an airtight stainless steel body. A beryllium window, which has a good x-ray transmission profile, is fixed on an opening in the cell. The cathode material can be deposited directly on the beryllium window, itself acting as a positive-electrode contact. A glass fiber separator soaked in liquid electrolyte is then positioned in contact with the cathode followed by a metal anode (3). A number of variations and improvements have been introduced to protect the beryllium window, which is subject to corrosion when the high-voltage cathode is in direct contact with it. 

There have been many investigations of photoinduced effects in -Si H films linked to material parameters. Changes have been observed in the carrier diffusion length, unpaired spin density, density of states in the gap, and infrared transmission. The transition from state A to B seems to be induced by any process that creates free carriers, including x-ray radiation and injection (double) from the electrodes. Because degradation in a solar cell is accentuated at the open-circuit voltage conditions, the A to B transition occurs upon recombination of excess free carriers in which the eneigy involved is less than the band gap. It has been pointed out that this transition is a relatively inefficient one and the increase in spin density takes place at a rate of 10-8 spins per absorbed photon. 

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