„Energy Storage“
Storage of (electrical) Energy, Fuel Cells & E-Mobility
Prof. Dr. Gerhard Illing
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How to use these slides …
The following slides do not represent a complete "script",
but should mainly reflect the contents of the lecture.
The slides will be supplemented, revised and edited as the lecture progresses.
The slides are supplemented by calculations, pictures and texts in the lecture.
It is always possible that errors have crept in - if you discover one,
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Part “Fuel Cells”
Main topics
• Characteristics of the different types of fuel cells
• Thermodynamics and electrochemistry
• Materials used in fuel cells
• Technical concepts / technical implementation
• Hydrogen as energy carrier / storage of hydrogen
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Part “Energy Storage”
Main topics
• What is energy
• Important terms and definitions
• Physical equations for calculation
• Energy storage: task, characteristics, classification and benefits
• Examples of typical energy storage devices
• Further examples and applications (student presentations)
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Energy
Statements on the concept of energy:
Energy is "the (principal) ability to perform (useful) work"
Energy can be regarded as a measured variable that can appear in
different ways, but whose numerical value always remains the same
Energy: any combination of physical quantities resulting in the unit
“ kg ∙ m²/ s² ".
Energy, work and heat are energetically equivalent to each other and can
be transformed into each other
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Energy
The term "energy" was introduced around 1850 by Lord Kelvin (*1824,
†1907)
Energy: word of Greek origin: "en" in, "ergos" work
SI unit of energy: Joule, unit symbol "J", named after James Joule (*1818,
†1889)
Definition: 1 J, work required to lift an item by 1 m with a weight of 1 N
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Force / Heat, Energy, Work
Term
Force
Work
Symbol
Unit
F
N (Newton)
N = kg · m · s-2
F=m∙a
W
J (Joule)
N∙m
J=N∙m=
kg · m2 · s-2
W=F·s
Unit equation
Physical
equation
In physics is force (F) the product of mass (m) x acceleration (a).
work (W) is performed when a force is applied to a body along a path: Work
is the product of force (F) X distance (s).
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Force / Heat, Energy, Work
Term
Symbol
Unit
Force
F
N (Newton)
N = kg · m · s-2
F=m∙a
Heat
Energy
Work
Q
E
W
J (Joule)
W∙s
N∙m
J=N∙m=
W∙s=
kg · m2 · s-2
Q = m ∙ c ∙ ΔT
E=U∙I∙t
W=F·s
Watt (W)
W = J ∙ s-1 =
kg · m2 ·s-3
P = W ∙ t-1
Leistung
ሶ
P (= 𝐐)
Unit equation
Physical
equation
Heat, work and (electrical) energy are equivalent!
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Force, Work (=Energy), Power
In physics force (F) is the product of mass (m) x acceleration (a).
Work (W) is performed when a force is applied to an object along a
path: work is the product of force (F) X distance (s).
Power (P) describes how much work (W) is done per unit of time (t) or
how much energy is used per unit of time
P = ΔW / Δt
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Force / Heat, Energy, Work / Power
Term
Symbol
Unit
Force
F
N (Newton)
N = kg · m · s-2
F=m∙a
Heat
Energy
Work
Q
E
W
J (Joule)
W∙s
N∙m
J=N∙m=
W∙s=
kg · m2 · s-2
Q = m ∙ c ∙ ΔT
E=U∙I∙t
W=F·s
Power
ሶ
P (= 𝐐)
Watt (W)
W = J ∙ s-1 =
kg · m2 ·s-3
P = W ∙ t-1
Unit equation
Physical
equation
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Different types of energy
In calculations different symbols are used for energy: E, W, Q (or U and H), G.
Type of
energy
W (= Ekin)
Equation
Description
W=F·s
Work
Kinetic energy (movement
of objects and fluids)
W (= Ekin)
W = 0,5 ∙ m ∙
Erot
E = 0,5 ∙ J ∙ ω2
Rotation energy
Epot
ED
E=m∙g∙z
E = 0,5 ∙ D ∙ s2
Potential energy
Tension energy
Hr (= Qr)
H = m ∙ hr
Reaction heat
Hv
H = m ∙ hv
Evaporation heat
W (= Eel)
E=U∙I∙t
Electrical energy
v2
ER
Friction Energy
E=µ∙F∙s
Energieerhaltungssatz:
Q (= Eth)
Q = m ∙ c ∙ ΔT
G
G=H–T∙S
ER
ERel
E=h∙f
Heat
Chemical energy (free
enthalpy)
Energy of radiation
E = m ∙ c2
Relativistic mass-E context
Term
Symbol
Unit
Hight
Heat capacity
Reaction enthalpy,
spezific
Evaporation
enthalpy, specific
Voltage
Current
z
c
m
J ∙ kg-1 ∙ K-1
hr
J ∙ kg-1
hv
J ∙ kg-1
U
I
V
A
Velocity
Accelertion
v
a
m ∙ s-1
m · s-2
Gravity constant
g
9,81 m · s-2
Distance
s
m
Friction coefficiant
µ
-
Suspension constant
D
N ∙ m-1
Moment of inertia
J
kg ∙ m2
Angular velocity
ω
s-1
Planck's constant
h
6.62607015 * 10-34 J s
Frequency
f
s-1
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Stored energy released into the environment …
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Ideal gas law
The thermodynamic state of the gas can be clearly determined by the pressure, temperature and
volume using the ideal gas equation.
p · V = n · R · T = (m / M) · R · T = ρ · V · (R / M) · T = m · Ri · T = ρ · V · Ri · T
Symbol
Equation
Name
(Factor) Unit
p0
Normal pressure
101325 Pa
T0
Normal temperature
273,15 K
V
Volume
m³
n
Number of moles
mol
R
Univ. gas constant
8,314 J · mol-1· K-1
Ri
Ri = R / M
Spec. gas constant
J · kg-1 · K-1
ρ
ρ = m · V-1
Density
kg ∙ m-³
M
M=m/n
Molar mass
kg ∙ mol-1
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Prefix symbols: Decimal multiples or parts of units
Prefix
Symbol
Power of ten
Factor
milli
m
10-3
0,001
mW, power laser class 2
kilo
k
103
1.000
kW, power of an electrical heater
Mega
M
106
1.000.000
Giga
G
109
1.000.000.000
Tera
T
1012
Example
MW, power of medium sized wind turbine
GW, power of a nuclear power plant
1.000.000.000.000 TW, currently used electrical power worldwide
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Energy can be expressed in the units “J” or in “kWh”:
Conversion
1J
1W·s
1 W ∙ 3600 s = 3,6 ∙ 103 Ws (= J)
3600 Ws = 3600 Ws / 3600 s/h = 1 Wh
3,6 ∙ 103 ∙ 103 J = 3,6 ∙ 103 kJ
1 kWh
1J
2,778 ∙ 10-7 kWh
103 J = 1 kJ
2,778 ∙ 10-4 kWh
106 J = 1 MJ
0,278 kWh
(1J
0,239 cal )
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„Fuel Cells“
winter term 2023 / 2024
G. Illing
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Elektrolysis …
Platinumelektrode
+
+
Deluted
sulphuric
acid
Hydrogen
=
and Oxygen
Elektrolysis of water
Anode
Cathode
Oxidation
Reduction
Energy conversion: electric -> chemical
“forced” reaction
Free Energy: ΔRG > 0, endergonic (energy demanding)
Voltage:
ΔU < 0
(- pole)
(+ pole)
Reduction
total
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Elektrolysis of water
Anode
Cathode
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Fuel Cell …
Deluted
Platinum/O2 (+) +
sulphuric acid
Platinum/H2 (-)
=
Water
The first Fuel Cell …
Sulphuric
Platinum +
+ el. Current
acid
The first Fuel Cell
Christan Friedrich Schönbein (1799-1886) and Sir William Grove (1811-1896) discovered
that the electrolysis process is reversible. In 1839 Grove developed the first fuel cell.
Source: Wikipedia
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The first Fuel-Cell
In 1839 the fuel cell was "invented".
e-
Platinum
electrode
O2
e-
} ΔU
Grove experimented with the
electrolysis of water to hydrogen and
oxygen.
He discovered that this process could
also be reversed.
H2
This first fuel cell (galvanic gas
battery) consisted of glass tubes
containing platinum electrodes
immersed in sulphuric acid.
Sulfuric
acid
H3O+
H+
The platinum electrodes were flushed
with hydrogen and oxygen.
Source: Wikipedia
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The first Fuel-Cell
Electrolizer
Platinum
electrode
Sulfuric
acid
He discovered that this
process could also be
reversed.
H2
This first fuel cell (galvanic
gas battery) consisted of
glass tubes containing
platinum electrodes
immersed in sulphuric acid.
The platinum electrodes
were flushed with hydrogen
and oxygen.
Picture above, contemporary representation:
several "fuel cells" connected in series serve to provide electrical energy for electrolysis
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Conventional power generation / fuel-cell
conventional
power generation
fuel-cell principle
chemical energy
of fuel
thermal
energy
conversion in three
steps (indirectly)
direct
conversion
kinetic
energy
electrical
energy
In energy technology, the term fuel cell is used to describe an energy conversion system in which chemically bound energy of a fuel and an
oxidant can be continuously converted directly into electrical energy. The most widespread use of hydrogen as fuel and oxygen as oxidant is the
most common. By combining other reaction partners, there are further possibilities to realize fuel cells. The technical challenges lie in corrosion
phenomena on the electrodes and in the stability of the materials used, as well as in the complexity of the electrochemical processes.
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H2 / O2 – Fuel-Cell
Free Enthalpy can be used as electrical energy:
∆G = -237.31 kJ/mol , if...the partial reactions are separated from each other.
Related to 1 mol H2:
Anode (- pole)
H2
-> 2H+ + 2e
Oxidation
0V
Cathode (+ pole)
0,5O2 + 2e + 2H+
-> H2O
Reduction
1,23V
total
H2 + 0,5 O2
-> H2O
1,23V
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H2 / O2 – Fuel-Cell (and battery)
Kathode
Anode
Reduction
Oxidation
Energy conversion: E chemical -> E elektric
“self-running” reaction
Free Energy: ΔRG < 0, exergonic (energy generating)
Voltage:
ΔU > 0
(- pole)
(+ pole)
Reduction
total
O2 + 4e + 4H+ -> 2H2O
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Visions
Jules Verne (1828 - 1905) wrote about the fuel cell in 1870:
"Water is the coal of the future. The energy of tomorrow is water, which has been
separated by electric current.
The elements of water broken down in this way, hydrogen and oxygen, will secure the
Earth's energy supply for the foreseeable future".
Bildquelle: Wikipedia
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Visions
However, Friedrich Wilhelm Ostwald (1853-1932),
director of the first chair of physical chemistry in
Leipzig, recognised the potential of Grove's fuel
cell as early as 1887:
"If we have a galvanic element which directly
supplies electrical energy from coal and the
oxygen in the air [...], then we are facing a
technical revolution, against which the steam
engine must disappear.
Bildquelle: Wikipedia
Just think how [...] the appearance of our
industrial sites will change! No more smoke, no
more soot, no more steam engine, no more
fire..." .
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2023 reality ?!?
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