Stationary current-voltage characteristics

The bubble growth on an electrode can be followed by considering the mean stationary current—voltage characteristics obtained by measuring the mean... 

An interesting consequence of these calculations is that the normalised mean stationary current—voltage characteristics are similar for different electrodes and electrolytes. An example is shown in Fig. 3.19 where the normalised mean current—voltage characteristics for a sodium hydroxide solution with different concentrations is depicted. 

Fig. 7.18 Stationary current voltage characteristics for the symmetrical cell Pt, 02 ceria Pt,02 (ceria is CaO-do-ped) [579]. The transfer reaction determines the overall kinetics and makes for a markedly nonlinear behaviour. The fitting reveals Sz = az = 1. In the model z=2 and the symmetry factor 1/2. From Ref. [579].

It is further important to note that all the current/voltage characteristics depicted in Fig. 6 are unchanged by the presence of liquid fuels such as methanol, formaldehyde, formic acid, or hydrazine. The phthalocyanine electrode remains completely inert toward such substances. For this reason, no mixed potential can be formed at a phthalocyanine electrode, as for example can occur at a platinum electrode, when it is used as cathode in a methanol cell containing sulfuric acid. This is shown by a comparison (see Fig. 7) of the stationary characteristics of the platinum alloy we found to be the most active in the presence of methanol, namely a Raney ruthenium—rhodium electrode, with an iron phthalocyanine electrode, both measured in 4.5 N H2SO4+2M CH3OH. 

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

By combining these relations, one gets the normalised mean stationary current characteristics for terminal voltages lower than the critical voltage (i.e. U < 1) ... 

M.E. Green and M. Yafuso, A study of the noise generated during ion transport across membranes, J. Phys. Chem., 1968, 72, 4072-4078 I. Rubinstein. Mechanism for an electrodiffusional instability in concentration polarization, J. Chem. Soc., Faraday Trans. 2. 1981, 77, 1595-1609 F. Maletzki, H.-W. Rosier and E. Staude, Ion transport across electrodialysis membranes in the overlimiting current density range Stationary voltage current characteristics and current noise power spectra under different conditions of free convection, J. Membr. Sci., 1992, 71, 105-115. 

The tasks of basic engineering can be divided into several sequential steps. The first step involves considering some general calculations. The core of a fuel cell system is the fuel cell itself A fuel cell is characterized by its voltage-current characteristics. For stationary applications, a design point must be defined. For... 

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