Electrodes, bipolar reference

Electrodes Bipolar Mode ESU Hazards ESU Design Defining Terms References Further Information... 

The ECG leads shown on the 12-lead ECG are made up of a combination of the ten electrodes placed on the body. These leads can be referred to either as unipolar or bipolar leads. It is important to understand the difference between the 12 leads (views) of the heart shown on the ECG, and the ten cables attached to the electrodes, also referred to as leads. 

Research and development efforts have been directed toward improved ceU designs, theoretical electrochemical studies of magnesium ceUs, and improved cathode conditions. A stacked-type bipolar electrode ceU has been operated on a lab scale (112). Electrochemical studies of the mechanism of magnesium ion reduction have determined that it is a two-electron reversible process that is mass-transfer controUed (113). A review of magnesium production is found ia Reference 114. 

The experimental setup used for the first bipolar or wireless NEMCA study is shown in Figure 12.6.8 An YSZ disc with two terminal Au electrodes and one Pt catalyst film deposited on one side and a reference Au electrode on the other side is placed in a single-chamber reactor. Ethylene oxidation on the Pt catalyst film was chosen as a model reaction.8... 

Fig. 1. Schematic presentation of a PEFC cross-section. The cell (left) consists of a membrane catalyzed on both sides (referred to as a membrane/electrode (M E) assembly ), gas-diffusion backing layers and current collectors with flow fields for gas distribution. The latter become bipolar plates in a fuel cell stack. The M E assembly described schematically here (right) shows catalyst layers made of Pt/C catalyst intermixed with ionomer and bonded to the membrane (large circles in the scheme correspond to 10 nm dia. carbon particles and small circles to 2 nm dia. platinum particles).

In Section III, electrochemical promotion studies with single -pellet type electrochemical cells were presented. This type of cell, especially when equipped also with a reference electrode as shown in Figure 1, is well suited for fundamental studies of the phenomenon. For practical applications of electrochemical promotion, however, this configuration is obviously inadequate, hi this chapter, development of more advanced, bipolar cell configurations will be presented. These results may be considered as the first successful steps towards achievement of electrochemical promotion with highly dispersed catalysts. 

A bipolar gap direct ohmic photoelectro-chemical system comprises either a bipolar band gap pnpn/electrolyte ohmic photo-electrochemical cell, with reduction occurring at the photoelectrode-electrolyte interface and regenerative oxidation occurring at the electrolyte-counter electrode (anode) interface or alternately a npnp/electrolyte bipolar band gap with oxidation occurring at the semiconductor-electrolyte interface and regenerative reduction occurring at the electrolyte-counter electrode interface. In the bipolar gap direct ohmic photoelectro-chemical system, direct refers to the direct contact between semiconductor and solution, and ohmic indicates this interface is an ohmic rather than a Schottky junction. This facilitates study of several characteristics of bipolar multiple band gap systems, without the added complication of simultaneous parameterization of a direct Schottky barrier at the electrolyte interface. 

If suddenly the channels (Figure 5.5) open so that the intracellular potential changes abruptly, the ions must also supply a transient discharge current of the membrane capacitance. At the extracellular side, the current is not with respect to a far-away reference electrode, but concentrated to an interstitial fluid zone near the cell. The current flow can be modeled with local current dipoles and is clearly measurable with unipolar or bipolar pickup electrodes in the interstitial liquid. When the cell is depolarizing, cations... 

Two bipolar CC electrodes plus PU reference electrode (see Section 8.3). 

It is worth stressing that a modified BLM in the above cell arrangement behaves as a bipolar electrode or two working electrodes connected in series. The two reference electrodes depicted in the setup merely facilitate the connection to the measuring instrument. The cell potential... 

The electrical potential generated by eye movement, called electrooculography (EOG), is also recorded in the EEG system. It is acquired through a pair of active and reference bipolar electrodes, plugged into a bipolar polygraphic EEG channel where the EOG signal is ampMed and digitized. 

The cell voltage Ucell is defined as the potential difference between the cathode and the anode. It is usually measured during fuel-ceU operation. The potential difference between the electrode and the electrolyte, which is caUed the anode or cathode potential in the following, is responsible for the electrochemical reaction occurring within the catalyst layers but cannot be measured directly. In the further text, we use electrolyte and membrane as equivalent expressions. While the electrode potential can be sensed from the bipolar plates, it is not feasible to sense the membrane potential directly, since each measurement equipment forms an interface between the membrane and the metal contact Two methods for the installation of a reference electrode within the ceU have been discussed in the Hterature, namely the reverse hydrogen electrode (RHE) [18] and the dynamic hydrogen electrode (DHE). In addition to ceU internal methods, a conventional... 

This reaction is currently unavoidable and appears to be favored at hot and dry operating conditions of the fuel cell. The peroxide decomposition forms reactive radials such as hydroxyl, OH, and peroxyl, OOH, that cause oxidative degradation of both the fuel cell membrane and catalyst support [67]. Both electrodes currently use Pt or Pt alloys to catalyze both the HOR and ORR reactions. The catalyst particles are typically supported on a high surface area, heat-treated carbon to both increase the effectiveness of the catalyst and to provide a path for the electrons to pass through to the external circuit via the gas diffusion media (which is typically also made of carbon) and the current collecting bipolar plates. In addition, the catalyst particles are coated in ionomer to facilitate proton transport however, the electrode structure must also be porous to facilitate reactant gas transport. A schematic of a typical PEM MEA is shown in Fig. 17.1. A boundary condition exists at the catalyst particle where protons from the ionomer, electrons from the electrically conducting Pt and carbon, and reactant gases meet. This is usually referred to as the three-phase boundary. The transport of reactants, electrons, and protons must be carefully balanced in terms of the properties, volume, and distribution of each media in order to optimize operation of the fuel cell. 

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