Fuel cell electrical efficiency

In the direct internal reforming MCFC (DIR-MCFC) system, the direct reformation of fuel at the anode can give fuel saving of 20%, resulting in 12 /o improvement in fuel cell electrical efficiency. The schematic representation of the HR and DIR concepts is shown in Fig. 4. 

The voltage based on AH° is 1.17 V [(675600/(6/96485)], and this voltage is used to calculate fuel cell electrical efficiency. 

The fuel cell electrical efficiency is directly proportional to the fuel ceU voltage AFceii ... 

Equation 1.3 indicates that, for an electrochemical reaction, part of the reaction energy (AH) is used to generate electrical energy (AG), and the other part is used to produce heat (TAS). In a fuel cell system, the most useful energy is electrical energy, while the heat produced is sometimes not desired. Therefore, electrical efficiency (or the reversible or thermod5mamic efficiency), can be defined as the ratio of the maximum electrical energy from the cell reaction to the reaction enthalpy. This represents the theoretical upper limit for fuel cell electrical efficiency. 

Assuming a theoretical efficiency of the fuel-cell system of around 60% and an electric-drive-train efficiency of 90%, the overall fuel-cell system efficiency is about 55%. The theoretical efficiencies for a fuel cell cannot be realised in practice. The efficiency of the system (including fuel treatment, air supply and others) is already lower than that of the pure fuel-cell stack on its own the overall efficiency of the FC drive train falls to less than 40% as a result of additional components, such as compressors, control electronics and others, see Fig. 13.6. 

The HEI describes the amount of energy required to haul 1 kg of the vehicle over a distance of 1 km. The HEI is a measure of efficiency - it is the inverse of a vehicle L divided by the weight of the vehicle (b) Increase the efficiency of energy conversion devices such as the engine, fuel cell, electric motor and gasoline... 

As the synergistic hydrogen production process using natural gas and nuclear heat is efficient and economic, and also the subsequent electro-chemical conversion of hydrogen into electricity in an alkaline fuel cell is efficient, electricity generation by combining these two processes have the following possibilities ... 

To obtain electricity, the hydrogen in the pipes at 100 atm would be used to drive generators, thus achieving an appropriate reduction in pressure of the hydrogen before it is converted to electricity via fuel cells (-65% efficiency). For space heating, the hydrogen would be used directly. 

Figure 3.52. Efficiency of a reversible PEM fuel cell as a function of the amount (at. % or mol %) of Ir in the form of IrOj relative to Pt in the positive electrode catalyst, for fuel cell electricity production (EC) or for water electrolysis (WE). Also the product of the two efficiencies relevant for storage cycles is shown. The catalyst is otherwise similar to that of Fig. 3.51, with PTFE and Nation channels. (From T. loroi, K. Ya-suda, Z. Siroma, N. Fujiwara, Y. Miyazaki (2002). Thin film electrocatalyst layer for unitized regenerative polymer electrolyte fuel cell. J. Power Sources 112, 583-587. Used by permission from Elsevier. See also loroi et al. (2004).

Fig. 6.6 Stack and fuel cell system efficiency versus DC-DC converter inlet electric power under the experimental conditions of Fig. 6.4...

An important point to consider about the stack management, with reference to an electric power train operating in dynamic conditions, as determined by road requirements, is the regulation of the stack temperature together with the other control parameters of water and reactants to avoid mass transfer limitations and membrane drying out or flooding. Moreover, the interaction between stack and auxiliaries has to be balanced taking into account the optimization of fuel cell system efficiency and reliability (see Sect. 4.6). 

A project has started in 1996 to develop and install a 12 - 15 kW SPFC into a Peugeot minivan equipped with a special tank to store hydrogen at 70 MPa [12]. In the project FEVER (Fuel Cell Electric Vehicle for Efficiency and Range), Renault pursues a car design with a 30 kW PEM fuel cell and a 120 1 LH2 tank to allow a 500 km cruising range [59]. In both projects, the goal is to start test operation in 1997. 

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