Potential theoretical cell

Anode metal (black) Cathode metal (red) Actual cell potential (V) Anode halfreaction and theoretical potential Cathode halfreaction and theoretical potential Theoretical cell potential % Error... 

In practice, the decomposition potential for this overall reaction is found to be about 1.5 V this somewhat high value probably results from polarization and contact resistances. It could be seen that the electrochemical decomposition of alumina to deposit aluminum, using an inert anode, would require a theoretical cell voltage of 2.21 V as opposed to that of 1.18 V when carbon is used as the anode. Thus the participation of carbon in the cell reaction brings down the theoretically required cell voltage by almost 50%. 

Electrode potential measured in solutions where all reactants and products are at unit activity (p. 231). Theoretical Cell Potential... 

A potential developed when a current/ flows in an electro-chemical cell. It is a consequence of the cell resistance R and is given by the product IR. It is always subtracted from the theoretical cell potential and therefore reduces that of a galvanic cell and increases the potential required to operate an electrolysis cell. 

If the activities of all reactants and products are unity, Theoretical cell potentials can be... 

Calculate the theoretical cell potentials for the following systems ... 

A fascinating point, especially to physical chemists, is the potential theoretical efficiency of fuel cells. Conventional combustion machines principally transfer energy from hot parts to cold parts of the machine and, thus, convert some of the energy to mechanical work. The theoretical efficiency is given by the so-called Carnot cycle and depends strongly on the temperature difference, see Fig. 13.3. In fuel cells, the maximum efficiency is given by the relation of the useable free reaction enthalpy G to the enthalpy H (AG = AH - T AS). For hydrogen-fuelled cells the reaction takes place as shown in Eq. (13.1a). With A//R = 241.8 kJ/mol and AGr = 228.5 under standard conditions (0 °C andp = 100 kPa) there is a theoretical efficiency of 95%. If the reaction results in condensed H20, the thermodynamic values are A//R = 285.8 kJ/ mol and AGR = 237.1 and the efficiency can then be calculated as 83%. 

Theoretical cell potential The algebraic sum of the individual redox potentials of an electrochemical cell at zero current, i.e. emf = Epositive electrode - negative electrode- In practice, when Current flows in a cell, a liquid junction potential is present, and the cell potential is larger than this theoretical value. 

While these results provided a potential theoretical background for ROS formation by aminoglycoside-nansition metal complexes, there were severe practical constraints. The stability constants-for example, of the Cu-amikacin complexes-were such that gentamicin would have to be present in cells or tissues at impossibly high levels (around 100 M) before a significant fraction of Cu... 

Theoretical Cell Potentials of Various Oxidation Reactions at 25 °C... 

In a fuel cell, the H2 and 02 pressures are not limited to 1 atm. Change in these pressures leads to deviation from the theoretical cell voltage. The relationships between the gas pressures, the anode and cathode potentials, and the cell voltage... 

Under theoretical cell voltage conditions, for both half-cell reactions (HOR and ORR) there is no net reaction. In other words, both half-electrochemical reactions are in equilibrium, and no net current passes through the external circuit. The cell voltage can be considered the OCV. At 25 °C, if the pressures of both H2 and 02 are 1 atm, the OCV should be 1.23 V. However, in reality the OCV is normally lower and an OCV of 1.23 V is never observed. This is due to the mixed potential at the cathode side, and hydrogen crossover from the anode side to the cathode side [22, 23], At 1.23 V, Pt is not stable so oxidation of Pt occurs ... 

CLs), resulting in a drastic drop in cell performance [17], Figure 3.13 also shows the difference between the theoretical cell potential (1.23 V) and the thermoneutral voltage (1.4 V), which represents the energy loss under reversible conditions (the reversible loss) [18], Very often, polarization curves are converted to power density versus current density plots by multiplying the cell voltage by the current density at each point of the curve. 

If the activities of all reactants and products are unity, = . Theoretical cell potentials can be calculated using tabulated values of E. For dilute solutions ([Pg.225]

The voltage efficiency i)v = C/cell/ theoretic reflects voltage losses due to polarization phenomena at the electrodes and ohmic potential drops at the interfaces in the electrolyte, and in the interconnectors (the theoretic cell voltage for water production is 1.23 V, voltages between 0.6 and 0.9 V are usually observed in real systems depending on current densities). 

Polarization is the departure of the electrode potential from its theoretical Nernst equation value on the passage of current. Overvoltage is the potential difference between the theoretical cell potential from Equation 22-2 and the actual cell potential at a given level of current. 

The theoretical cell voltage of the reaction is 1.214 V according to the free Gibbs energy of the reaction of ArG = —702.5 kJ/mol. In reality various effects lead to a reduction of the achievable open circuit voltage. The formation of CO-species as intermediate at the anode [12, 13] and the methanol permeation through the membrane are well known causes for reduced power density and the formation of mixed potentials. Special anode catalysts for lower sensitivity towards... 

---