Elementary Principles of Chemical Processes, Binder Ready Version
Elementary Principles of Chemical Processes, Binder Ready Version
4th Edition
ISBN: 9781118431221
Author: Richard M. Felder, Ronald W. Rousseau, Lisa G. Bullard
Publisher: WILEY


Textbook Question
Book Icon
Chapter 6, Problem 6.20P

A fuel cell is an electrochemical device in which hydrogen reacts with oxygen to produce water and DC electricity. A 1-watt proton-exchange membrane fuel cell (PEMFC) could be used for portable applications such as cellular telephones, and a 100-kW PEMFC could be used to power an automobile

The following reactions occur inside the PEMFC:

Anode: H 2 2H + +2e

Cathode: 1 2 O 2 +2H + +2e H 2 O

Overall: H 2 + 1 2 O 2 H 2 O

A ?owchart of a single cell of a PEMFC is shown below. The complete cell would consist of a stack of such cells in series, such as the one shown in Problem 9.19.

Chapter 6, Problem 6.20P, A fuel cell is an electrochemical device in which hydrogen reacts with oxygen to produce water and

The cell consists of two gas channels separated by a membrane sandwiched between two ?at carbon-paper electrodes—the anode and the cathode—that contain imbedded platinum particles. Hydrogen ?ows into the anode chamber and contacts the anode, where H2molecules are catalyzed by the platinum to dissociate and ionize to form hydrogen ions (protons) and electrons. The electrons are conducted through the carbon ?bers of the anode to an external circuit, where they pass to the cathode of the next cell in the stack. The hydrogen ions permeate from the anode through the membrane to the cathode.

Humid air is fed into the cathode chamber, and at the cathode O2molecules are catalytically split to form oxygen atoms, which combine with the hydrogen ions coming through the membrane and electrons coming from the external circuit to form water. The water desorbs into the cathode gas and is carried out of the cell. The membrane material is a hydrophilic polymer that absorbs water molecules and facilitates the transport of the hydrogen ions from the anode to the cathode. Electrons come from the anode of the cell at one end of the stack and ?ow through an external circuit to drive the device that the fuel cell is powering, while the electrons coming from the device ?ow back to the cathode at the opposite end of the stack to complete the circuit.

It is important to keep the water content of the cathode gas between upper and lower limits. lf the content reaches a value for which the relative humidity would exceed 100%, condensation occurs at the cathode (?ooding), and the entering oxygen must diffuse through a liquid water ?lm before it cart react. The rate of this diffusion is much lower than the rate of diffusion through the gas film normally adjacent to the cathode, and so the performance of the fuel cell deteriorates. On the other hand, if there is not enough water in the cathode gas (less than 85% relative humidity), the membrane dries out and cannot transport hydrogen efficiently, which also leads to reduced performance.

A 400-cell 300—volt PEMFC operates at steady state with a power output of 36 kW. The air fed to the cathode side is at 200°C and roughly 1.0 atm (absolute) with a relative humidity of 70.0% and a volumetric ?ow rate of 4.00 × 10 3 SLPM (standard liters per minute). The gas exits at 60°C.

(a) Explain in your own words what happens in a single cell of a PEMFC.

(b) The stoichiometric hydrogen requirement for a PEMFC is given by ( n H 2 ) consumed = I N / 2 F , where I is the current in amperes (coulomb/s), N is the number of single cells in the fuel cell stack, and F is the Faraday constant, 96,485 coulombs of charge per mol of electrons. Derive this expression. (Hint: Recall that since the cells are stacked in series the same current ?ows through each one, and the same quantity of hydrogen must be consumed in each single cell to produce that current at each anode.)

(c) Use the expression of Part (b) to determine the molar rates of oxygen consumed and water generated in the unit with the given speci?cations, both in units of mol/min. (Remember that power = voltage × current.) Then determine the relative humidity of the cathode exit stream, h r,out .

(d) Determine the minimum cathode inlet ?ow rate in SLPM to prevent the fuel cell from ?ooding ( h r,out = 100 % ) and the maximum ?ow rate to prevent it from drying ( h r,out = 85 % ) .

Blurred answer

Chapter 6 Solutions

Elementary Principles of Chemical Processes, Binder Ready Version

Ch. 6 - Prob. 6.11PCh. 6 - Prob. 6.12PCh. 6 - Prob. 6.13PCh. 6 - Air at 50% relative humidity is cooled...Ch. 6 - Prob. 6.15PCh. 6 - Prob. 6.16PCh. 6 - Air at 90°C and 1.00 atm (absolute) contains 10.0...Ch. 6 - When fermentation units are operated with high...Ch. 6 - When you step out of a shower, the temperature in...Ch. 6 - A fuel cell is an electrochemical device in which...Ch. 6 - Prob. 6.21PCh. 6 - Prob. 6.22PCh. 6 - Prob. 6.23PCh. 6 - Prob. 6.24PCh. 6 - Prob. 6.25PCh. 6 - Prob. 6.26PCh. 6 - Prob. 6.27PCh. 6 - Prob. 6.28PCh. 6 - An air conditioner is designed to bring 10.000...Ch. 6 - Prob. 6.30PCh. 6 - Prob. 6.31PCh. 6 - Prob. 6.32PCh. 6 - A gas stream containing 40.0 mole% hydrogen, 35.0%...Ch. 6 - Prob. 6.34PCh. 6 - In the manufacture of an active pharmaceutical...Ch. 6 - Prob. 6.36PCh. 6 - In the ?nal stage of the manufacturing process...Ch. 6 - Prob. 6.38PCh. 6 - A fuel gas containing methane and ethane is burned...Ch. 6 - A mixture of propane and butane is burned with...Ch. 6 - An important parameter in the design of gas...Ch. 6 - A liquid stream consisting of 12.5 mole% n-butane...Ch. 6 - Nitric acid is a chemical intermediate primarily...Ch. 6 - Prob. 6.44PCh. 6 - Sulfur trioxide (SO3) dissolves in and reacts with...Ch. 6 - State whether you would use Raoult’s law or Henrys...Ch. 6 - A gas containing nitrogen, benzene, and toluene is...Ch. 6 - Prob. 6.48PCh. 6 - Prob. 6.49PCh. 6 - A conelation for methane solubility in...Ch. 6 - Prob. 6.51PCh. 6 - The constituent partial pressures of a gas in...Ch. 6 - Prob. 6.53PCh. 6 - Prob. 6.54PCh. 6 - Prob. 6.55PCh. 6 - Prob. 6.56PCh. 6 - Prob. 6.57PCh. 6 - Prob. 6.58PCh. 6 - Nitrogen is bubbled through a liquid mixture that...Ch. 6 - Prob. 6.60PCh. 6 - Prob. 6.61PCh. 6 - Prob. 6.62PCh. 6 - The feed to a distillation column (sketched below)...Ch. 6 - Prob. 6.64PCh. 6 - Prob. 6.65PCh. 6 - Prob. 6.66PCh. 6 - Prob. 6.67PCh. 6 - Prob. 6.68PCh. 6 - Prob. 6.69PCh. 6 - Prob. 6.70PCh. 6 - A methanol-water feed stream is introduced to a...Ch. 6 - Prob. 6.72PCh. 6 - In this problem you will use a spreadsheet to...Ch. 6 - Prob. 6.74PCh. 6 - Prob. 6.75PCh. 6 - Prob. 6.76PCh. 6 - Acetaldehyde is synthesized by the catalytic...Ch. 6 - Dehydration of natural gas is necessary to prevent...Ch. 6 - A two-unit process is used to separate H2S from a...Ch. 6 - Prob. 6.80PCh. 6 - Prob. 6.81PCh. 6 - Prob. 6.82PCh. 6 - Prob. 6.83PCh. 6 - A solution containing 100 lbm KNO3/100 Ibm H2O at...Ch. 6 - A 10.0 wt% aqueous solution of sodium chloride is...Ch. 6 - Potassium dichromate (K2Cr2O7) is to be recovered...Ch. 6 - Prob. 6.87PCh. 6 - Prob. 6.88PCh. 6 - Sodium bicarbonate is synthesized by reacting...Ch. 6 - An ore containing 90 wt% MgSO4(H2O and the balance...Ch. 6 - An aqueous waste stream leaving a process contains...Ch. 6 - A solution of diphenyl (MW = 154.2) in benzene is...Ch. 6 - An aqueous solution of urea (MW = 60.06) freezes...Ch. 6 - Prob. 6.94PCh. 6 - Derive Equation 6.54 for the boiling-point...Ch. 6 - Prob. 6.96PCh. 6 - A stream of 5.00 wt% oleic acid in cottonseed oil...Ch. 6 - Benzene and hexane are being considered as...Ch. 6 - Acetone is lo be extracted with n-hexane from a...Ch. 6 - Prob. 6.100PCh. 6 - Prob. 6.101PCh. 6 - Five kilograms of a 30 wt% acetone70% water...Ch. 6 - An aqueous acetone solution is fed at a rate of...Ch. 6 - Prob. 6.104PCh. 6 - Prob. 6.105PCh. 6 - Air at 25°C and 1 atm with a relative humidity of...Ch. 6 - Prob. 6.107PCh. 6 - Prob. 6.108PCh. 6 - Various amounts of activated carbon were added to...

Additional Engineering Textbook Solutions

Find more solutions based on key concepts
Knowledge Booster
Background pattern image
Chemical Engineering
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, chemical-engineering and related others by exploring similar questions and additional content below.
Recommended textbooks for you
Text book image
Introduction to Chemical Engineering Thermodynami...
Chemical Engineering
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:McGraw-Hill Education
Text book image
Elementary Principles of Chemical Processes, Bind...
Chemical Engineering
Author:Richard M. Felder, Ronald W. Rousseau, Lisa G. Bullard
Text book image
Elements of Chemical Reaction Engineering (5th Ed...
Chemical Engineering
Author:H. Scott Fogler
Publisher:Prentice Hall
Text book image
Process Dynamics and Control, 4e
Chemical Engineering
Text book image
Industrial Plastics: Theory and Applications
Chemical Engineering
Author:Lokensgard, Erik
Publisher:Delmar Cengage Learning
Text book image
Unit Operations of Chemical Engineering
Chemical Engineering
Author:Warren McCabe, Julian C. Smith, Peter Harriott
Publisher:McGraw-Hill Companies, The
Mod-01 Lec-23 Degrees of freedom analysis; Author: nptelhrd;https://www.youtube.com/watch?v=c4h85JjrkzQ;License: Standard YouTube License, CC-BY
Introduction to Degrees of Freedom; Author: LearnChemE;https://www.youtube.com/watch?v=tW1ft4y5fQY;License: Standard Youtube License