Detailed thermodynamic analysis of polymer electrolyte membrane fuel cell efficiency (original) (raw)
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Detailed Thermodynamic Analysis of Fuel Cell Efficiency
Efficiency of hydrogen fuel cells is analyzed using a non-equilibrium theory of mixtures based on classical irreversible ther-modynamics. The efficiency is expressed in terms of processes taking place inside the fuel cells revealing which processes are responsible for efficiency losses. This provides a new method of optimization. It is shown that efficiency losses are not only given by entropy production rate but also by some additional terms, which become important if steep gradients of temperature are present. Consequently, we compare the new theory with the standard entropy production minimization approach. Finally, we discuss effects of the additional terms in polymer electrolyte membrane fuel cells and in solid oxide fuel cells showing that the new theory gives the same results as the standard theory in the former case while it becomes important in the latter case.
Thermodynamic Study of Operation Properties Effect on Polymer Electrolyte Membrane Fuel Cells (PEM)
2021
The thermodynamic analysis of PEM fuel cell energy production depends on the entropy and enthalpy of reaction with the changing of the operating temperatures that ranges between 50 and 100ºC, the electrical work done will be equal to the Gibbs free energy released. This paper presents a mathematical model of PEM fuel cells, based on physical-chemical procedures of the phenomena occurring inside the fuel cell, and it was theoretically studied the performance at different operation variables and conditions. The C++ program is designed to calculate all thermo-chemical parameters, i.e. enthalpy of formation, Gibbs free energy, work and efficiency for any type of fuel cells. The results are plotted as a function of fuel cell operating temperature. The results shows that the highest value of Gibbs energy is at the lowest operating temperature, and decreases gradually with increasing the temperature, the output voltage is determined by cell’s reversible voltage that arises from potential d...
In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation and technology are described. The basic electrochemistry principles determining the operation of the fuel cell, the kinetics of redox reactions during the fuel cell operation, the mass and energy transport in a fuel cell, etc., are described briefly to give an understanding of practical fuel cell systems. The ideal and practical operation of fuel cells and their efficiency are also described. This will provide the framework to understand the electrochemical and thermodynamic basics of the operation of fuel cells and how fuel cell performance can be influenced by the operating conditions. The influence of thermodynamic variables like pressure, temperature, and gas concentration, etc., on fuel cell performance has to be analyzed and understood to predict how fuel cells interact with the systems where it is applied. Understanding the impact of these variables allows system analysis studies of a specific fuel cell application.
The Characteristic Thickness of Polymer Electrolyte Membrane and the Efficiency of Fuel Cell
Heat Transfer Engineering, 2009
We propose a simple diffusion model of a PEM fuel cell and perform its thermodynamic analysis. Our description is based on a set of two mass balance equations involving water and proton transport through the membrane coupled with two reaction equations describing the electrochemical reactions at the electrodes. Equations for the water and proton flux densities are constructed in a linearized form suitable for the analysis from the point of view of irreversible thermodynamics. In terms of our simplified model, relations for the characteristic thickness of a PEM membrane is derived, and the maximum efficiency of a fuel cell is evaluated, both as functions of the transport properties of the PEM material.
Thermodynamics is the study of energetics; the study of the transformation of energy from one form to another. Since fuel cells are energy conversion devices, fuel cell thermodynam-ics is key to understanding the conversion of chemical energy into electrical energy. For fuel cells, thermodynamics can predict whether a candidate fuel cell reaction is energetically spontaneous. Furthermore, thermodynamics places upper bound limits on the maximum electrical potential that can be generated in a reaction. Thus, thermodynamics yields the theoretical boundaries of what is possible with a fuel cell; it gives the "ideal case." Any real fuel cell will perform at or below its thermodynamic limit. Understanding real fuel cell performance requires a knowledge of kinetics in addition to thermodynamics. This chapter covers the thermodynamics of fuel cells. Subsequent chapters will cover the major kinetic limitations on fuel cell performance, defining practical performance. 2.1 THERMODYNAMICS REVIEW This section presents a brief review of the main tenets of thermodynamics. These basic theories are typically taught in an introductory thermodynamics course. Next, these concepts are extended to include parameters that are needed to understand fuel cell behavior. Readers are advised to consult a thermodynamics book if additional review is required. 2.1.1 What Is Thermodynamics? It is no secret that no one really understands the meaning of popular thermodynamic quantities. For example, Nobel Prize-winning physicist Richard Feynman wrote in his Lectures
The Journal of Physical Chemistry B, 2005
We show how to determine the local entropy production rate in the various parts of a polymer electrolyte fuel cell producing liquid water from air and hydrogen. We present and solve five sets of transport equations for the heterogeneous, one-dimensional cell at stationary state, equations that are compatible with the second law of thermodynamics. The simultaneous solution of concentration, temperature, and potential profiles gave information about the local entropy production and the heat and water fluxes out of the system. Results for the entropy production can be used to explain the polarization curve, and we find that diffusion in the backing is less important for the potential than charge transport in the membrane. We demonstrate that all coupling effects as defined in nonequilibrium thermodynamics theory are essential for a correct description of the dissipation of energy and also for the small temperature gradients that were calculated here. The heat flux out of the anode was smaller than the heat flux out of the cathode. The cathode surface temperature increased as the current density increased but was smaller than the anode surface temperature for small current densities. This type of modeling may be important for design of cooling systems for fuel cells. The method is general, however, and can be used to analyze batteries and other fuel cells in a similar manner.
Renewable and Sustainable Energy Reviews, 2019
Polymeric Electrolyte Membrane Fuel Cell (PEMFC) modeling considering thermal and electrical behavior in a coupled manner is a key aspect when evaluating new designs, materials, physical phenomena or control strategies. Depending on the behavior to be emulated, it is important to choose the modeling technique that best suits the needs required. In this sense, this paper describes the most commonly used PEMFC modeling techniques in the context of analytical-mechanistic approach, semi-empirical approach based on theoretical formulation and empirical correlations, as well as empirical approach based on experimentation with a real system. In addition, an in-depth analysis of PEMFC models at the cell and stack level that emulate the thermal and electrical behavior of these systems in a coupled manner is carried out. A chronological classification of the most relevant models has been made based on the modeling technique used, purpose of the model, state and dimension of the model, and the real system, other developed models or experimental results that have been used to validate the proposed new model. Additionally, guidelines to improve the energy efficiency of PEMFC systems through the development of new models are given.
Journal of The Electrochemical Society, 2020
We show that the coupling effects in non-equilibrium thermodynamics for heat-, mass- and charge- transport in the polymer electrolyte membrane fuel cell (PEMFC) all give significant contributions to local heat effects. The set of equations was solved by modifying an open-source 1D fuel cell algorithm. The entropy balance was used to check for model consistency. The balance was obeyed within 10% error in all PEMFC layers, except for the cathode backing. The Dufour effect/thermal diffusion and the Peltier/Seebeck coefficient are commonly neglected. Here they are included systematically. The model was used to compute heat fluxes out of the cell. A temperature difference of 5 K between the left and right boundary of the system could change the heat fluxes up to 44%. The Dufour effect, for instance, increases the temperature of both anode and cathode, up to 9 K. The possibility to accurately predict local heat effects can be important for the design of fuel cell stacks, where intermediat...