High ohmic resistance

The separator is eliminated, thus avoiding various serious problems related to the use of membranes, such as a the high ohmic resistance. 

A fifth reason for using microfluidics in electrochemistry would be the possibility to combine flow chemistry with an ultrafast mixer, which allows the generation and subsequent use of short-lived reactive ions or radicals, for example, in a "cation flow" process (Suga et al., 2001 Yoshida, 2008). Finally, a sixth reason for performing electrochemistry in a microfluidic system may be the desire to efficiently remove reaction heat (or joule heat due to high currents in combination with a high ohmic resistance) in fast electrochemical reactions (Yoshida, 2008). 

M. Ben-Porat, J. Yahalom, and E. Rubin, Current Distribution during Electroplating Within a Tbbular Electrode of High Ohmic Resistance, J. Electrochem. Soc., 130, No. 3, 559-567 (1983). 

As with other active-passive-type metals and alloys, the pitting corrosion of aluminum and its alloys results from the local penetration of a passive oxide film in the presence of environments containing specific anions, particularly chloride ions. The oxide film is y-Al203 with a partially crystalline to amorphous structure (Ref 13, 59). The film forms rapidly on exposure to air and, therefore, is always present on initial contact with an aqueous environment. Continued contact with water causes the film to become partially hydrated with an increase in thickness, and it may become partially colloidal in character. It is uncertain as to whether the initial air-formed film essentially remains and the hydrated part of the film is a consequence of precipitated hydroxide or that the initial film is also altered. Since the oxide film has a high ohmic resistance, the rate of reduction of dissolved oxygen or hydrogen ions on the passive film is very small (Ref 60). 

Attempts are being made at replacing the very expensive EVD process by other techniques. The cells are connected to bundles via nickel felts. The high ohmic resistance of this concept requires an operating temperature between 900 and 1000°C to reach power densities of about 200 mW/cm. To overcome this problem SWPC is working on a modified concept, using flattened tubes with internal ribs for reduced resistance (see Fig. 1). 

As evident from Fig. 2.21 in Chapter 2 of this book, oxides with stoichiometric coefficients <1.4 have high ohmic resistance. Thus, a high-resistance interface layer forms between the active mass and the grid, which reduces the energy and power output of the battery during discharge. However, this layer does not affect the total amount of lead dioxide contained in the formed positive active mass. Hence, the discharge time of passivated and unpassivated plates... 

Despite the ionic resistance of the electrolyte plays an important role in the cell ohmic resistance, it is the contribution of the anode and cathode resistance which determines the high ohmic resistance of the cell this is due to the long path of the electrons in the electrodes [29] (high in-plane resistance). The equivalent electrical circuit has been assumed by the current literature [30,31] and the ohmic overpotential has been evaluated according to the equations (42) and (43) ... 

The Nafion content in catalyst ink should be controlled appropriately. Too little Nafion and the ionic conductivity of the catalyst layer is insufficient, leading to low Pt utilization and high ohmic resistance too much Nafion and the gas aecessibility and electronic conductivity of the catalyst layer are insufficient [52,... 

The characterisfics of each component or components in essence determine the losses in the fuel cell. For example, a fuel cell with abnormally high ohmic resistance may have an electrol5de with high resistance, or electrical contacts may have high resistance. The cell and component characterization helps determine these losses and provide guidance to focus on components for improvement. 

One practical way of preventing possible galvanic corrosion is to insulate the two metals in contact from one another as carefully as possible [17]. This is achieved by placing a high ohmic resistance, i.e. an insulating material (Figure B.3.3) such as neoprene or any other suitable polymer, between them. 

Severe dehydration of the membrane can result in significant high ohmic resistance. First, this is because the fuel cell ohmic over potential is mainly caused by ionic resistance in the electrolyte. Second, the conductivity of membrane, a critical factor of the ionic resistance, is a very strong function of its own water content. 

However, as shown in Fig. 5, this configuration leads to a long current path around the tube, thus generating high ohmic resistance. 

In this situation, however, the current path is all along the tube surface, thus producing high ohmic resistance. This phenomenon can be reduced by wrapping a wire around and inside the tube (Bove and Sammes 2005). 

---