Gibbs fuel cells

Fuel Cell Efficiency The theoretical energy conversion efficiency of a fuel cell ° is given by the ratio of the free energy (Gibbs function) of the cell reaction at the cell s operating temperature AG to the enthalpv of reaction at the standara state AH°, both quantities being based on a mole of fuel ... 

The theoretical efficiency of a fuel cell is given by the ratio between the Gibbs free energy (AG) which is the maximum electrical work that can be obtained, and the enthalpy (A//) of the fuel (Equation 6.3). 

The voltage generated by a battery or fuel cell, the cell potential, is simply related to the Gibbs energy of the cell reaction, AGr, by... 

Temperature and Pressure The effect of temperature and pressure on the ideal potential (E) of a fuel cell can be analyzed on the basis of changes in the Gibbs free energy with temperature and pressure. 

In the ideal case of an electrochemical converter, such as a fuel cell, the change in Gibbs free energy, AG, (Section 2.2.3) of the reaction is available as useful electric energy at the temperature of the conversion. The ideal efficiency of a fuel cell, operating irreversibly, is then... 

The maximum electrical energy available from a fuel cell is determined by the Gibbs free energy difference across the electrolyte membrane, AG. This determines the equilibrium voltage of the cell, E, through the Nemst equation, which is nothing more than a restatement in electrical units of how AG (= 2FE) changes with pressure. 

A solid oxide fuel cell is an electrochemical device which converts the Gibbs free enthalpy of the combustion reaction of a fuel and an oxidant gas (air) as far as possible directly into electricity. Hydrogen and oxygen are used to illustrate the simplest case. This allows the calculation of the reversible work for the reversible reaction. Heat must be transferred reversibly as well to the surrounding environment in this instance. 

The reversible efficiency jjFCrev of the fuel cell is defined as the ratio of the Gibbs free enthalpy ArG and the reaction enthalpy A H at the thermodynamic state of the fuel cell. 

The reversible work tUfSystrev of a coupled fuel cell-heat engine system is independent of the state of the cell and is always equal to the Gibbs free enthalpy of the reaction ArG° at the ambient state [4], It is assumed that the standard condition is equal to the ambient state to keep the argumentation simple. This result indicates the necessary equipment to utilise the exergy of the fuel. 

Thermodynamic considerations are applied to understand the processes of energy conversion in SOFCs. The reversible work of a fuel cell, represented by the Nemst voltage, can be calculated by the Gibbs free enthalpy of the reaction. The consideration of the electrical effects shows that the molar flow of the spent fuel is proportional to the electric current and that the reversible work is proportional to the reversible voltage. A coupling between the thermodynamic data and the electrical data is only possible by using the quantities power or heat flow and not by using work and heat. 

In accordance with thermodynamic laws, only the Gibbs free energy, AG °, of the overall fuel cell reaction can be converted into the equivalent electric cell potential, AE° these two quantities are linked via... 

However, the efficiency of a fuel cell is determined by the thermodynamic equation of Gibbs free energy ... 

One of the emerging uses of solid-state electrocatalytic systems is in fuel cells, to convert a significant portion of the Gibbs free energy change of exothermic reactions into electricity rather than heat. The thermodynamic efficiency of such power generating schemes compares favorably with thermal power generation which is limited by Carnot-type constraints. 

Devise a fuel cell arrangement in which the reaction 2H2 + 02 - 2H20 may be carried out to a finite extent, such that the measured Gibbs free energy change is identical with AGd. 

Gibb P, 2001, Advances in Ballard Fuel Cell Technology - The Mk 900. Seventh Grove Fuel Cell Symposium, London. 

Theoretically all the combustible materials can serve as a fuel to the SOFC via the direct electrochemical oxidation on the anode. Table 1 lists a number of fuel reactions with AG° (i.e., the change in the Gibbs free energy) and AH° (the change in the enthalpy), E° (theoretically reversible potential or voltage), and the fuel cell efficiency. Fuel cell efficiency is defined as ... 

In a fuel cell, an electrolyte is used to divide the strongly exothermic chemical reaction H2+V2O2 HjO into two electrochemical reactions a reduction and an oxidation reaction. In this way, the conversion of the reaction Gibbs energy, A,G, into electrical energy is possible, and the only reaction product is water (if pure... 

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