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EGEE 420: Fuel Cells, Lecture Notes
N/A
92
Science
Undergraduate 3
02/05/2011

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Term
President GWB announced the Hydrogen Fuel Initiative (HFI) in ___
Definition
2003
Term
Energy Policy Act of 2005: title VII: Spark M. Matsunaga H2 Act...
Definition
authorized $3.2 B for H2 and fuel cell tech.
Term
Advanced Energy Initiative in 2006...
Definition
was passed to accelerate research for renewable technologies
Term
The development of hydrogen and fuel cell technologies has been
___ well-supported by the U.S. government.
Definition
reasonably
Term
Who said, "Yes, my friend, I believe that water will one day serve as our fuel, that the
hydrogen and oxygen which compose it... will supply an inexhaustible source of heat and light... I believe that when the coal mines have been exhausted,
we will both heat and be heated with water. Water is the coal of the future"?
Definition
Jules Verne in The Mysterious Island
Term
Sir William Grove discovered fuel and electrolytic cells in ___
Definition
1839
Term
the main fuel cell feature is...
Definition
a possibility to directly convert chemical energy of a fuel to electricity with a possible cogeneration of heat
Term
Hydrogen can reliably be used to store the electrical energy because...
Definition
...it is a good energy carrier
Term
molecular hydrogen is ___ in nature
Definition
not naturally found
Term
hydrogen technology needs ___ gov't support to develop
Definition
substantial
Term
gov't support of H2 tech
Definition
was good but then decreased for 2008-09
now it is recovering
Term
hydrogen technology and infrastructure is in the ___ stage of the development.
Definition
early
Term
main feature of fuel cells
Definition
1. fundamentally different way of generating electricity from a variety of fuels
2. converts the chemical energy of a fuel to electricity and heat
3. technology is easily scalable (1 W - several MW)
Term
fuel cell efficiency
Definition
electrical efficiency: up to 50%
total efficiency (elec. + thermal): up to 80%
Term
electrolytic cells are also called ___ and ___
Definition
electrolysis cells
electrolyzers
Term
main features of electrolytic cells
Definition
1. efficiency of making H2 from electricity is near 100%
2. engineering principles of fuel and electrolytic cells are very similar
2. tech. is well-developed
Term
PEM fuel cell means
Definition
proton exchange membrane fuel cell
polymer-electrolyte membrane fuel cell
Term
PEMFC diagram
Definition
!!!!!!!!
Term
PEM electrolyzer diagram
Definition
!!!!!!!
Term
PEMEC vs. PEMFC
Definition
1. main components are essentially the same
2. cathode and anode positions are switched
3. for PEMEC, the PEM can be a porous ceramic or polymeric diaphragm
Term
PEMEC and PEMFC cathode and anode
Definition
PEMFC: H2 goes by the anode
O2 goes by the cathode
PEMEC: H2 goes by the cathode
O2 goes by the anode
Term
stationary PEMFCs
Definition
production in the USA is very limited because of high cost
(solid oxide FCs are cheaper)
Term
Fuel cell-powered cell phones...
Definition
are not available yet
Term
fuel cell-powered chargers...
Definition
are available and affordable
Term
fuel cell-powered cars...
Definition
1. can be leased in California
2. use reformers that convert gasoline to H2 for the fuel cell
3. electric-gasoline-fuel cell combo car will be on the market soon
Term
H2 fuel stations for cars...
Definition
there are 200 in the world
there are 3 in Pennsylvania
there is 1 at PSU
Term
challenges of FCs and ECs
Definition
1. cost of cells is high
2. infrastructure should be developed
3. durability should be improved
4. cost of H2 is high
5. right now, the electricity to power electrolysis comes from fossil fuels
Term
fuel cell components
Definition
1. ion conductive membrane
2. electrodes
3. bipolar plates
Term
hydrogen is weird because...
Definition
...it does not fit easily into the periodic table
1. it has one valance e- but is not a metal at room temp. like the alkali metals
2. it needs one e- to complete its valence shell like the halogens
Term
CODATA list of SI units
Definition
length: m
mass: kg
time: s
current: Ampere
temp.: Kelvin
quantity: mol
luminosity: candela
pressure: Pa = N/m^2
energy: J = N*m
power: W = J/s
potential: V = W/A
charge: C = s*A
Term
critcal T and P for H2
Definition
Tcrit: 32.95 K
Pcrit: 12.7 atm = 1287 kPa
Term
hydrogen isotopes
Definition
H - hydrogen
H(2)=D - dueterium
H(3)=T - tritium
Term
nuclear fusion of hydrogen makes ___
Definition
helium
Term
use of H2 in industry
Definition
1. H2 + CO -> methanol feedstock
2. H2 + non-hydrogenated FAs -> hydrogenated FAs
3. H2 + metal ion -> metals
4. H2 + N2 -> NH3 (fertilizer + plastics)
5. -> rocket fuel + fuel cells
Term
reactivity of hydrogen
Definition
relatively low for H2, but atomic hydrogen is very reactive
need a catalyst split H2 to 2 H
Term
molecular compounds of hydrogen
Definition
can be e- precise, e- rich, or e- poor
Term
saline hydrides
Definition
nonconducting, crystalline solids
Term
metallic hydrides
Definition
nonstoichiometric, electrically conducting solids
Term
e- precise compound
Definition
all valence e- of the central atom are engaged in bonds
Term
e- rich compound
Definition
there are more e- pairs on the central atom than are used in bonds
Term
e- deficient compound
Definition
there are too few e- to write a proper Lewis diagram for the molecule
Term
Reactivity of a hydrogen compound
depends on...
Definition
its electron structure
Term
s-block hydrogen compounds are ___
Definition
saline hydrides
Term
d- and f-block hydrogen compounds are ___
Definition
metallic hydrides
Term
p-block hydrogen compounds...
Definition
vary in their properties and stability
Term
properties of water are...
Definition
useful in the understanding of hydrogen technologies, fuel cells, and electrolytic systems
Term
hydrogen economy is to be developed, the following components are needed:
Definition
production, delivery, use, storage, education, codes
and standards, safety, technical validation, fuel cell vehicles
Term
In this class, use 273.15 K (all five digits)
Definition
also answers should have 4 sigdigs
Term
the historic trend of hydrocarbon fuel use suggests...
Definition
...that we progressively
move towards fuels with lower carbon content
Term
electrochemical cell
Definition
1. made of two electrodes connected by an electrolyte
2. usually oxidation is placed on the left and reduction on the right, for clockwise e- flow
Term
electrode compartment
Definition
an electrode and its electrolyte
(two electrodes may share the same compartment)
Term
salt bridge
Definition
1. a tube containing a concentrated electrolyte solution that completes the electrical circuit
2. used when the two electrolytes are different; it links the two electrode compartments
Term
galvanic cell
Definition
electrochemical cell that uses a spontaneous chemical rxn to produce electricity
Term
electrolytic cell
Definition
electrochemical cell that uses electricity to drive a non-spontaneous chemical rxn
Term
redox and cathode & anode
Definition
cathode- reduction takes place
anode- oxidation takes place
AOIL-CRIG
Term
cathode & anode polarity
Definition
galvanic cell: cathode is + and anode is -
electrolytic cell: cathode is - and anode is +
Term
IUPAC rules for constructing electrochemical diagrams
Definition
Cu(s)|Zn(s)|ZnSO4(aq)||CuSO4(aq)|Cu(s)
Term
total galvanic cell rxn
Definition
Cu(s)|Zn(s)|ZnSO4(aq)||CuSO4(aq)|Cu(s)
total rxn = (right half rxn)-(left half rxn)
left: Zn2+(aq) + 2e- = Zn(s)
right: Cu2+(aq) + 2e- = Cu(s)
total: Cu2+(aq) + Zn(s) = Cu(s) + Zn2+(aq)
Term
cell potential difference
Definition
Cu(s)|Zn(s)|ZnSO4(aq)||CuSO4(aq)|Cu(s)
total pot. dif. = (right pot.)-(left pot.)
left: Zn2+(aq) + 2e- = Zn(s) -> -0.76
right: Cu2+(aq) + 2e- = Cu(s) -> 0.34
total pot. dif. = 0.34 - -0.76 = 1.10 V
Term
for a galvanic cell...
Definition
positive pot. dif. means oxidation takes place (anode) on the left and reduction (cathode) on the right
negative pot. dif. means the opposite
Term
writing half rxns: on what side do you put e-?
Definition
for red: always put e- on the left side
for ox: always put e- on the right side
Term
Daniell cell
Definition
Zn and Cu electrodes
electrodes are separated so that ZnSO4 and CuSO4 don't mix
the electrode compartments are joined by a salt bridge, which usually has KCl
Term
KCl is usually used in the Daniell cell salt bridge because...
Definition
...because K+ and Cl- conduct electricity almost equally -> symmetry -> no accumulation of liquid junction potential (potential at ends of salt bridge)
Term
Nernst equation
Definition
E = Eo - (RT/vF)lnQ
ex, E = Eo - (RT/2F)ln(aCuaZn2+/aZnaCu2+)
Term
it's impossible to measure the potential of a single electrode, so...
Definition
...we define an electrode as zero, the standard hydrogen electrode (SHE), and measure potentials relative to that
Term
how to measure potentials using a SHE
Definition

put the SHE on the left and the electrode you want to measure on the right

measure the potential

then use Eo = ΔrGo/(vF)

where ΔrGo = (ΣprodviΔfGio) - (ΣreacviΔfGio)

*be careful using this method at elevated temps!

Term
Electrochemical Series CRC Handbook 89.pdf
Definition
3 tables listing standard reduction potentials, E° values, at STP
-Table 1: alphabetical list of the elements, according to symbol
-Table 2: list of reduction rxns that have (+) E° values, in increasing order
-Table 3: list of reduction rxns that have (-) E° values, in increasingly negative order
Term
Standard Thermo Properties of Chemical Substances CRC Handbook 89.pdf
Definition
This table gives the standard state chemical thermo properties of ~2500 substances in the crystal, liquid, and gas states
the properties listed are DELTAHfo, DELTAfGo, So, and Cp
Term
Thermo Properties of Aq Systems CRC Handbook 89.pdf
Definition
This table contains standard state thermo properties of ions and neutral species in aq. solution
It includes enthalpy and Gibbs energy of formation, entropy, and heat capacity
order: cations, anions, neutral species
Term
Thermo Properties as a Function of Temp CRC Handbook 89.pdf
Definition
The thermodynamic properties Cp°(T), S°(T), H°(T)-H°(Tr), -[G°(T)-H°(Tr)]/T and formation properties Δf H°(T), ΔfG°(T), log Kf°(T) are tabulated as functions of temp from 298.15 to 1500 K for 80 substances in the standard state
Term
Ex. Calculate potential diff. of a galvanic cell at STP
method 1
Definition

Cu(s)|Zn(s)|ZnSO4(aq)||CuSO4(aq)|Cu(s)

rxn = (right rxn) - (left rxn)

Eo = (Cu2+ + 2e- -Cu(s)) - (Zn2+ + 2e- -Zn(s))

Eo = 0.34 - -0.76 -> 1.10 V

 

 

 

Term
Ex. Calculate potential diff. of a galvanic cell at STP
method 2
Definition

Cu(s)|Zn(s)|ZnSO4(aq)||CuSO4(aq)|Cu(s)

rxn = (right rxn) - (left rxn)

ΔrGo = Cu2+ + Zn(s) - Cu(s) - Zn2+

ΔrGo = ΔfGoCu2+ + ΔfGoZn(s) - ΔfGoCu(s) - ΔfGoZn2+

 ΔrGo = -147.1 + 0 – 65.5 – 0 -> -212.6 kJ/mol

Eo = -ΔrGo/(vF) = -(-212.6k)-/(2*96485)

Eo = 1.10 V

Term
pressure dependence of Eo...
Definition
is defined by the volume of the rxn*
Term
temperature dependence of Eo...
Definition
is defined by the entropy of the rxn*
Term
calculating DELTArGo at elevated T and P
Definition
4 options:
1. Use the Gibbs energy of formation that are already calculated at elevated temperatures (CRC tables) and use Eo = -DELAtrGo/(vF)
2. if >150 C, use most accurate eqn
3. if <150 C, use approx. eqn
4. if <75 C, use most approx. eqn (see slide 5.7)
Term
the background of the equilibrium electrochemistry is ___
Definition
thermodynamics ((chemical equilibrium and solution thermodynamics)
Term
to calculate potential difference of an electrochemical cell, you need ___ and ___
Definition
standard electrode potentials
activities (activity coeffs and concentrations)
Term
to calculate the standard electrode potentials at elevated T or P...
Definition
additional thermodynamic properties are needed
Term
are higher T and P good for fuel cells?
Definition
higher T is good as long as the material isn't compromised
higher P is good, but it costs too much (usually use 5 atm, max)
*but for electrolyzers, P about 20 atm is ok because you would pressurize the H2 anyway
Term
what is the meaning of the activity coeff?
Definition
shows how far you deviate from ideal concentration
Term
for a pure substance, activity is always ___
Definition
1
Term
activity
Definition
a = (conc.)/(standard conc.)*(activity coeff)
Term
If the anode (red.) is on the left and the cathode (ox.) is on the right, electron flow is ___
Definition
clockwise
Term
exchange current density is defined as...
Definition
the rate where the anodic and cathodic rates are equal
Term
typical value for alpha (transfer coeff.) is ___
Definition
0.5
Term
a large exchange current density (fast rxn) is ___
Definition
over 1E-6
Term
as io increases, reversibility ___
Definition
decreases
Term
alpha indicates...
Definition
the symmetry of the barrier to the rxn
Term
Tafel plot shows...
Definition
io
alpha
Term
3-electrode electrochem. cell is used to...
Definition
study single electrodes
Term
3-electrode electrochem. cell terms
counter electrode
working electrode
reference electrode
Definition
counter- the electrode together with the working electrode
working- the electrode you want to study
reference- the electrode in the test tube thing
Term
concentration polarization is aka ___
Definition
concentration overpotential
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