Temperature dependence of the equilibrium cell voltage

The temperature dependence of the equilibrium cell voltage forms the basis for determining the thermodynamic variables AG, A//, and AS. The values of the equilibrium cell voltage A%, and the temperature coefficient dA< 00/d7 which are necessary for the calculation, can be measured exactly in experiments. 

The oxidation rate depends not only on the gas composition and the temperature parameter, but also on the electric potential difference between the electronically conductive part of the anode electrode and the ionically conductive electrolyte. Defining the electric potential of the solid part of the anode electrode as zero potential, the reaction rate depends on the electric potential in the electrolyte, other hand, the reduction reaction rate depends on the electric potential difference at the cathode electrode, which is the difference between the given cell voltage, Uceii, and the electrolyte potential, equilibrium constants are determined by the... 

To predict the local polarisation in a full-scale cell or stack at any point, its dependence on composition, pressure, and temperature of the gas flowing in the gas channel contacting the electrode must be known. In a large cell, these bulk gas properties vary from one point to the next. Electrode polarisation or overpotential - the difference between the local potential of the electrode under load and the potential at open circuit (equilibrium potential) - is also a local quantity because it depends not only on the bulk gas composition but also on the current density. In a large cell the current is usually distributed nonuniformly, as discussed in Sections 11.2-11.5. Similar to Eq. 7, one can express the local cell voltage under load, i.e., when current is passed, as the thermodynamic cell potential minus three loss terms the ohmic loss, the cathode polarisation, and the anode polarisation ... 

Electrode potential, E The energy, expressed as a voltage, of a redox couple at equilibrium. E is the potential of the electrode when measured relative to a standard (ultimately the SHE). E depends on temperature, activity and solvent. By convention, the half cell must first be written as a reduction, and the potential is then designated as positive if the reaction proceeds spontaneously with respect to the SHE. Otherwise, E is negative. 

Therefore such sensors are called Nernstian sensors. As a reference air with defined humidity is used. In reducing gases that are in chemical equilibrium (e.g., H2, H2Oj CO, C02 water gas) the oxygen partial pressure is determined by the mass law constant Kv and this in turn depends on the temperature. In the case of H2,H20-mixtures the cell voltage is obtained by insertion of a temperature function of log Kp into the Nernst equation... 

PEM fuel cell characteristics are generally described with polarization curves. The thermodynamic equilibrium potential of the hydrogen/oxygen reaction is reduced by various overvoltage terms that depend on mass transport, kinetic, and ohmic phenomena within cell. In other words, the output voltage of a single cell is attributable to different current, temperature, and pressure dependant factors [1]. 

The position of equilibrium of a reaction maybe affected by changes in the concentration of reagents, temperature and pressure of gases. The voltage of an electrochemical cell will also depend on these factors, so we should use standard conditions when comparing electrode potentials. These are ... 

Equilibrium of a reaction can be shifted by a change in pressme or temperature the equilibrium constant depends on temperature and pressure. Because of the Nemst relation, such a change results in a voltage change in an electrochemical cell. Example 6.5 illustrates this. 

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