Ex-cell method

Fig. 3 Electrooxidation of p-methoxytoluene with cerium salt by an ex-cell method.

As mentioned by Mathias et al. [9], reliable methods to measure the thermal conductivity of diffusion layers as a function of compression pressures are very scarce in the open literature. Khandelwal and Mench [112] designed an ex situ method to measure accurately the thermal conductivities of different components used in a fuel cell. In their apparatus, the sample materials were placed between two cylindrical rods made out of aluminum bronze (see Figure 4.28). Three thermocouples were located equidistantly in each of the upper and lower cylinders to monitor the temperatures along these components. Two plates located at each end compressed both cylinders together. The temperatures of each plate were maintained by flowing coolant fluids at a high flow rate through channels located inside each of the plates. A load cell was located between two plates at one end so that the compression pressure could be measured. 

In situ measurements (i.e., those done on an electrode while it is in contact with the solution under a controlled potential) are described below (see also Section 6.2.4). However, there are plenty of reports in the electrochemical literature of the use of ex situ methods for looking at electrochemical situations. In these, the electrochemical reactions are duly carried out, sometimes using a thin-layer cell, and then the solution is rapidly removed from the thin-layer cell, e.g., by applying a vacuum. The electrode (one of the plates in the thin-layer cell) and whatever remains on it as a result of electrochemical activity while it was in contact with the solution, can then be examined at leisure, using a number of spectroscopic methods, including those that only function in vacuo. 

The cleanliness and single crystallinity of electrode surfaces are not assumed even if the preparative steps outlined above are followed. The verification or identification of initial, intermediate, and final interfacial stmctures and compositions is an essential ingredient in our studies. The interfacial characterization methods employed to date have been conveniently classified in terms of whether they are conducted under reaction conditions (in situ) or outside the electrochemical cell (ex situ). In situ methods here consisted of cychc voltammetry (CV), EC-STM and DBMS. Ex situ methods included LEED, AES, and HREELS. 

K. Klier (Lehigh University, Bethlehem, Pa. 18015) The authors have chosen the cell method, which seems to be quite successful in ex-... 

The ex situ method, pioneered by Hubbard [1] and Ross [56], entails electrode preparation in UHV, clean transfer of the specimen from UHV into an electrochemical cell and transfer back to UHV for postelectrochemical reaction analysis. The methodology was developed to study the stability of Pt-skin and 3d elements in sputtered surfaces. For this purpose, we restrict our analysis to the polycrystalline PtjFe surface, which is discussed in Sect. 2.1. As summarized in Fig. 3.1b, LEIS spectra indicate that after exposing this alloy to an electrochemical environment Fe surface atoms dissolve from the near-surface layers leading to a first atomic layer composed entirely of Pt [21]. For the remaining surface, which consists of only Pt atoms after dissolution of the alloying component, we employ the term Pt-skeleton structure. The conclusions drawn from these experiments are equally valid for all sputtered PtjM alloys i.e., whenever 3d transition metal atoms are exposed to acidic environments, nonplatinum atoms dissolve leading to the formation of Pt-skeleton surfaces. 

The in-situ techniques of Cauquis, Kastening, and Dohrmann described above, although showing advantages over ex-situ methods, did not contribute significant advances towards a kinetic analysis of electrode mechanisms. Improvements upon this are shown by cells developed by several groups of workers for in-situ electrochemical ESR and are described in the following section. 

Ex-situ methods such as diffraction methods show details about the electronic properties of nanostructures [104]. Catalysts made of electronically conducting Ru02 are surrounded by hydrous proton-conducting regions [105], which is necessary for the high activity of this material as a co-catalyst for CO-tolerant Pt-RuO c fuel cell electrocatalysts. 

The explanation of the acronyms is provided above (see p. xi). Only methods applicable under ex situ conditions are emphasized in the figure (italics). As already indicated, a sample transfer from the electrochemical cell into a ultrahigh vacuum (UHV) analysis system accompanied by drying of the sample and exposure to the atmosphere is necessary and any conceivable influence of this step may result in artifacts. This is most impressively demonstrated in studies of corrosion layers on iron electrodes. Ex situ methods have repeatedly yielded erroneous results for example, because of dehydration of the corrosion products [14],... 

Mass spectrometry has been applied in electrochemical investigations predominantly as an ex situ method because of the obvious incompatibility of the high vacuum needed for all types of mass spectrometry and the presence of a liquid electrolyte solution. Because of the amount of information provided in a mass spectrum, there have been various attempts to couple mass spectrometers with electrochemical cells as described below. 

The most common method to measure alcohol permeability through membranes is the diffusion cell method under non-stationary conditions. In this method the membrane separates two reservoirs the receptor reservoir containing pure water, and the donor reservoir containing the alcohol solution of known concentration. Usually the alcohol solution in the donor reservoir is refreshed during the experiment to maintain its concentration, Cj, constant along the time. The non-stationary alcohol concentration in the receptor reservoir, c, is followed as a function of time by in situ or ex situ sensors. By integrating Eq. 6.4 the time dependence of is given by... 

Cells are taken from the body of the genetically defective individual, treated, then returned to the body. An example of this ex vivo method is given below for the correction of severe combined immunodeficiency. If blood cells are used, and since blood cells have a limited lifespan, periodic cycles of ex vivo treatment and reinfusion are necessary. It may be more expedient to target the stem cells of the bone marrow, because these are apparently immortal. Neonates with SCID have now been treated by inserting genes into the stem cells, and at 2 years of age these were still thriving without the benefit of further treatment. 

Ex-cell-mediated oxidation operates efficiently when the concentration of organic pollutants is low and when, because of its properties, this treatment is complementary with respect to electrochemical treatment, which operates with low efficiency when the pollutant concentration low. With the ex-cell oxidation method, a strong oxidant precursor is initially produced, which is mixed with the wastewater to assure the proximity of precursor organic species afterwards, the action of thermal, ultraviolet, or another form of energy transforms the precursor to active oxidants. The previously achieved proximity between precursor and organic pollutants becomes an active oxidant-pollutant proximity that assures efficient oxidation, even when the concentration of organic species is low. 

Ex-cell-mediated oxidation has similarities and differences with respect to the indirect electrochemical oxidation known in this field. The principal similarity is that both methods use an active oxidant that oxidizes the organic species, i.e., both methods assure the proximity of active oxidant-organic species then, oxidation occurs efficiently even when the concentration of the organic species is low. The principal difference concerns the control of the operating conditions of the steps that compose the mediated oxidation occurring in these cases. In indirect oxidation, the steps of precursor production, mixing, activation, and oxidation occur in the electrochemical cell, where even direct oxidation can occur. In ex-ceU-mediated oxidation, a specific piece of equipment is dedicated at every step of the process, and the control of each step allows its efficient realization. 

Durability testing takes a long time in an operation environment, which is difficult as normally several thousand hours are necessary to obtain a meaningful conclusion. In the development of durability testing, some in situ and ex situ methods and techniques for material evaluation have been used, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), CV, EIS and so on. However, new electrochemical and/or physical techniques are desirable to gain a better understanding of durability failure modes and then improve fuel cell durability and reliability. 

The electrochemical activity of fuel cell electrodes may be investigated by ex situ and in situ CV experiments. Ex situ method is a relatively fast method for electrocatalysts screening but in situ method allows the electrocatalysts investigation in the fuel cell which provides a more realistic approach of the catalyst activity. In the in situ method, CV of the fuel cell can be performed in one electrode at a time, by making the other a pseudo-hydrogen reference electrode. Thus, the working electrode is the cathode as it is... 

Two main methods were used for fuel permeability determination ex situ and in situ methods. The former method, also named diffusion cell method, was mostly used for methanol permeability measurements [22,84,85]. In this measurement, a diffusion cell was used, consisting of two reservoirs of distinct composition, with a sample membrane between them. The membrane acts as a parting plane to prevent liquid passing through directly and only permit permeation of the molecules in solution. The two reservoirs were injected with aqueous methanol solution with a certain... 

MEA should be fabricated from the sample PEMs and then assembled into the single-cell system, which is the same as fuel cell. Potential step experiments were performed to evaluate fuel permeability using an electrochemical interface with a certain flow rate of humidified H2 at the anode and humidified N2 at the cathode. The anode served as both the counter and reference electrodes. The cathode potential was increased gradually, and the steady-state current density corresponds to the H2 crossover current density. Although more complicated than ex situ method, the in situ method is much more accurate and closer to the real situation of fuel cell operation. 

The ex vivo IL-6 and TNF-inducing activities of fractionated and modified or unmodified poly(MA-CDA) were performed according to the method reported [26] and shown in Figs. 12 and 13, respectively. A similar tendency was shown in IL-6 and TNF induction from peripheral whole blood cells by those of poIy(M A-CDA). 

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