The Optimal Thermodynamic Research And Application Of Proton Exchange Membrane(Pem)Fuel Cells

In recent years, energy problems has been widespread concerned. With the growing use of fossil fuels, the exhaustive exploitation of energy reserves, environmental problems are becoming more and more serious. Along with the emergence of the serious energy issue, searching for new clean proper energy sources have become the focus of attention worldwide and enhancing the performance of the energy conversion devices has been the main developing trend of the energy technologies. Fuel cell is an electrochemical device which converts fuel directly to electricity without undergoing combustion. Fuel cell technology has been given much attention because of its low operating temperature, quick start, light weight, high power density, zero pollution, reliable service and so on. It is considered as one of the most promising technologies for its wide range of applications. This paper has established a typical irreversible proton membrane fuel cell model, and explored various irreversible factors on the influence of the fuel cell system.Thermodynamic optimization analysis of fuel cells has been carried, and a typical proton exchange membrane fuel cell-refrigeration hybrid system has been established. Some theoretical significance and practical conclusions are obtained.The main research contents are organized as follows:In Chapter1, the brief introduction of the research background and development of the fuel cells are given.In Chapter2, an irreversible model of the proton exchange membrane fuel cell working at steady-state is established, in which overpotentials, internal currents, and crossover losses are taken into account. The expressions of some key parameters of the fuel cell are derived from the point of electrochemistry and thermodynamics. Based on the irreversible model of a proton exchange membrane fuel cell, the influence of multi-irreversibilities on fuel cell performance has been characterized and compared systematically. The general performance characteristic curves are generated. The optimal regions of some important parameters such as current density, efficiency, power output and the load resistances are obtained. Moreover, when the electrical circuit is closed with a load in it, the relations between the load resistance and power output and efficinecy are analyzed. The results obtained here may provide a theoretical basis for both the operation and optimal design of real PEM fuel cells.In Chapter3, an ecological performance analysis for a class of irreversible PEM fuel cells has been performed by employing the new thermo-ecological criterion as the objective function. The objective function is the ecological coeffcient of performance (ECOP), which is defined as the power output per unit loss rate of availability. A comprehensive numerical study is carried out to investigate the general and optimal performances of a class of PEM fuel cells. The effects of operating temperature, membrane thickness leakage current on the global and optimal performance have been discussed. The optimum performance parameters at ECOPmax conditions are investigated. The results are compared with those of the maximum-power output conditions. The results obtained here may provide a theoretical basis for b optimal design of real PEM fuel cells.In Chapter4, a proton exchange membrane fuel cell-four potential temperature absorption refrigeration hybrid system model is established, so that the waste heat produced in the PEM fuel cell can be availably utilized. Based on the theory of electrochemistry and non-equilibrium thermodynamics, expressions of the coefficient of performance and cooling rate of the refrigeration cycle, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electriccurrent density and the equivalent power output versus efficiency curves are presented through numerical calculation. The general performance characteristics of the hybridsystem are discussed. The optimal operation regions of some parameters in the hybrid system are determined. The advantages of the hybrid system are revealed.In the last Chapter, the conclusions obtained are summed up and the status and prospects of the present research are reviewed briefly.