PEM fuel cell as a membrane reactor

Thampan, Tony; Malhotra, Sanjiv; Zhang, Jingxin; Datta, Ravindra

doi:10.1016/s0920-5861(01)00278-4

Cited by 113 publications

(66 citation statements)

References 39 publications

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“…The DGM can be written as an implicit relationship among the molar concentrations, molar fluxes, concentrations gradients, and the pressure gradient 35,36 …”

Section: Model Descriptionmentioning

confidence: 99%

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

Zhu

Kee

Janardhanan

et al. 2005

J. Electrochem. Soc.

506

523

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This paper presents a new computational framework for modeling chemically reacting flow in anode-supported solid-oxide fuel cells ͑SOFC͒. Depending on materials and operating conditions, SOFC anodes afford a possibility for internal reforming or catalytic partial oxidation of hydrocarbon fuels. An important new element of the model is the capability to represent elementary heterogeneous chemical kinetics in the form of multistep reaction mechanisms. Porous-media transport in the electrodes is represented with a dusty-gas model. Charge-transfer chemistry is represented in a modified Butler-Volmer setting that is derived from elementary reactions, but assuming a single rate-limiting step. The model is discussed in terms of systems with defined flow channels and planar membrane-electrode assemblies. However, the underlying theory is independent of the particular geometry. Solid oxide fuel cells ͑SOFC͒ can be operated with a variety of fuels, including hydrogen, CO, hydrocarbons, or mixtures of these. This is possible because of the relatively high operating temperatures, and, at least in conventional SOFC anodes, the use of transition metal catalysts that promote the water-gas-shift reactionand steam reforming, which for methane may be written globally asIf sufficient steam is produced electrochemically at the anode/ electrolyte interface by the reactionthen reforming and shifting can, in principle, lead to full ͑if indirect͒ electrochemical oxidation of a hydrocarbon fuel. However, competing reaction pathways catalyzed by transition metals may also lead to solid carbon deposition, which can quickly destroy the anode. For this reason, some degree of upstream fuel processing, eiher by catalytic partial oxidation or by steam reforming, is usually used to produce a fuel stream that is rich in H 2 and CO and dilute in residual hydrocarbons before reaching the SOFC. Because upstream processing adds to the complexity, size, and cost of the overall plant, it is of considerable interest to minimize or even eliminate the need for it. There is evidence that mixing some oxygen with a hydrocarbon fuel can deliver good performance.1 In this case there must be partial oxidation within the anode structrue. Another promising alternative to utilize hydrocarbon fuels "directly" in SOFCs is to use a ceria oxidation catalyst instead of a transition metal. 2Whether an SOFC uses a "reforming anode" with a transition metal catalyst, or a "direct oxidation" anode with a ceria-based catalyst, or perhaps uses a different, novel anode design, optimizing the system to run efficiently on hydrocarbon or hydrocarbon-derived fuels is a very challenging problem, due to the complex, coupled physico-chemical processes involved. When significant CO and/or hydrocarbons are present in the fuel, models must also account for the in situ production of hydrogen through reforming and shifting reactions within the anode, as well as solid-carbon formation.Many questions of interest for optimization studies cannot currently be answered easily. For example, for...

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“…The DGM can be written as an implicit relationship among the molar concentrations, molar fluxes, concentrations gradients, and the pressure gradient 35,36 …”

Section: Model Descriptionmentioning

confidence: 99%

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

Zhu

Kee

Janardhanan

et al. 2005

J. Electrochem. Soc.

506

523

View full text Add to dashboard Cite

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“…Datta and co-workers have described of the structure of PEM fuel cells and the molecular details of the transport and reaction in the PEM fuel cell. (Thampan, Malhotra et al 2001) However, these models assume descriptions about transport processes and electrode kinetics and call for data about system variables that cannot be directly measured or controlled. We have followed an engineering approach and considered to what level of detail the system variables in the fuel cell can be described as functions of the parameters under operator control.…”

Section: Ii3 System Analysis Of Pem Fuel Cellsmentioning

confidence: 99%

The stirred tank reactor polymer electrolyte membrane fuel cell

et al. 2004

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The design and operation of a differential Polymer Electrolyte Membrane (PEM) fuel cell is described. The fuel cell design is based on coupled Stirred Tank Reactors (STR); the gas phase in each reactor compartment was well mixed. The characteristic times for reactant flow, gas phase diffusion and reaction were chosen so that the gas compositions at both the anode and cathode are uniform. The STR PEM fuel cell is one-dimensional; the only spatial gradients are transverse to the membrane. The STR PEM fuel cell was employed to exa mine fuel cell start-up, and its dynamic responses to changes in load, temperature and reactant flow rates. Multiple time scales in systems response are found to correspond to water absorption by the membrane, water transport through the membrane and stress-related mechanical changes of the membrane.

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“…R is the universal gas constant and z is electrochemical equivalent. From Thampan, et al [3], the relation between exchange current density i0 and temperature is given as For anode and cathode, it yields where ,0 and ,0 are exchange current density of anode, and cathode, respectively. ,0, and ,0, are reference exchange current density of anode, and cathode respectively.…”

Section: Activation Polarizationmentioning

confidence: 99%

The analysis of energy efficiency in water electrolysis under high temperature and high pressure

Hourng

Tsai

Lin

2017

IOP Conf. Ser.: Earth Environ. Sci.

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Abstract. This paper aims to analyze the energy efficiency of water electrolysis under high pressure and high temperature conditions. The effects of temperature and pressure on four different kinds of reaction mechanisms, namely, reversible voltage, activation polarization, ohmic polarization, and concentration polarization, are investigated in details. Results show that the ohmic and concentration over-potentials are increased as temperature is increased, however, the reversible and activation over-potentials are decreased as temperature is increased. Therefore, the net efficiency is enhanced as temperature is increased. The efficiency of water electrolysis at 350 o C/100 bars is increased about 17%, compared with that at 80 o C/1bar.

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PEM fuel cell as a membrane reactor

Cited by 113 publications

References 39 publications

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

The stirred tank reactor polymer electrolyte membrane fuel cell

The analysis of energy efficiency in water electrolysis under high temperature and high pressure

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