electrochemical microcalorimetry - kit
TRANSCRIPT
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
1 Rolf Schuster
Electrochemical Microcalorimetry
Kai Etzel, Katrin Bickel and Rolf SchusterPhysical Chemistry, Karlsruhe Institute of Technology, Germany
-Thermodynamics and kinetics of electrochemical reactions
10 nm
research interests:
-Surfaces in vacuum and electrochemical environment structure, phase transition, ordering processes‚electronic structure‘, scanning tunneling spectroscopy
metal deposition, H-adsorption/evolution
-Electrochemical microstructuring
(electrochemical STM, XPS, …)
(electrochemical STM, microcalorimetry, surface plasmon resonance,…)
Tem
pera
ture
[mK
]
Time [s]
0
-0.30 0.1 0.2
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
2 Rolf Schuster
Electrochemical Microcalorimetry
Kai Etzel, Katrin Bickel and Rolf SchusterPhysical Chemistry, Karlsruhe Institute of Technology, Germany
Historical: E. J. Mills, „On Electrostriction“, Proc. Roy. Soc. Lond. 26, 504 (1877)
E. Bouty, „Sur un phénomène analogue au phénomène de Peltier“,Comptes Rendus 89, 146 (1879)
Cu-deposition⇒ decreasing temperature
Cu-dissolution⇒ increasing temperature
Cu2+
SO42-
Cu-plated
„electrochemical Peltier heats“
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
3 Rolf Schuster
What do we learn from electrochemical microcalorimetry?
In „conventional“ calorimetry:
;STHGq RRRm Δ−=Δ−Δ=⇒
;Hq Rm Δ= p,T = const.
In electrochemical calorimetry:electrical work: ( );, STHGFzw RRRmel Δ−Δ−=Δ−=⋅⋅= φ
from the ‚chemical reaction‘heat transfer from surrounding
We measure the reaction entropy, ΔRS, (if we are close to equilibrium).
Ostwald (1903)
-stoechiometry of the reaction, i.e. hints on elementary steps-entropies of hydration, i.e., involvement of solvent water -phase transitions and surface entropies
in addition: irreversible heat due to chemical reactions, i.e., complexation, crystallization,...
⇒
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
4 Rolf Schuster
Can we achieve „monolayer sensitivity“?
Use thin electrode/sensor assembly with low heat capacity
Use pulsed electrochemical reactions:-fast enough to avoid heat loss into the electrolyte (and uptake of Joule heat
from the electrolyte)-slow enough to ensure thermal equilibration of the electrode/sensor assembly
potentiostat/galvanostat
+
-
charge amplifier
electrolyte
reference electrode
Au-foil
metalizedPVDF-foil
p 100 mbar≈
potentialpulse
temperaturesignalsocket
counter electrode
C. E. Borroni-Bird, and D. A. King, Rev. Sci. Instr. 62 (1991) 2177.J. T. Stuckless, N. A. Frei, and C. T. Campbell, Rev. Sci. Instr. 69 (1998) 2427.
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
5 Rolf Schuster
20x10-3
100
E [V
]
100x10-3806040200t [s]
0.80.40.0I [
mA
]
0.120.080.040.00
ΔT [a
rb. u
nits
]
Cu dissolution from a Cu-layer (≈ 300 ML) on a 50 µm Au foil
(0.5 M CuSO4 / 5mM H2SO4)
potential
current
temperature
10 ms dissolution at η = 20 mV
current set to zero after 10 ms
2.5·10-6 C/cm2 ≅ 0.04 ML Cu
00 <Δ⇒>Δ ST entropy gain due to Cu-dissolution!?
No: entropy loss due to water bonding in the hydration shell
21 1
( )122 JK molabs
Cu aqs +
− −≈ −
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Cu deposition/dissolution on Cu-bulk Ag deposition/dissolution on Ag-bulk20mM Cu(ClO4)2 / 1M HClO4 20mM AgClO4 / 1M HClO450 µm Au-foil +Cu 50 µm Au-foil + Ag
11)( molJK1222
−−−≈+abs
aqCus 11)( molJK51 −−+≈+
absaqAgs
-0.180-0.172E
[V]
0.300.250.200.150.100.050.00t [s]
-2.5
0.0
I [m
A]
1.00.80.60.40.20.0ΔT
[arb
. uni
ts]
-0.168-0.160
E [V
]
0.300.250.200.150.100.050.00t [s]
2.5
0.0I [m
A]
-1.0-0.8-0.6-0.4-0.20.0
ΔT [a
rb. u
nits
]
-0.600-0.592
E [V
]
0.300.250.200.150.100.050.00t [s]
-1.0
0.0I [
mA
]
-60x10-3-40-20
0
ΔT [a
rb. u
nits
]
-0.590-0.582
E [V
]
0.300.200.100.00t [s]
1.0
0.0I [m
A]
60x10-3
4020
0
ΔT
[arb
. uni
ts]
Cu dissolution: ΔRS < 0 Ag dissolution: ΔRS > 0
dominated by water bonding in the hydration shell
dominated by production of ions
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
7 Rolf Schuster
Polycrystalline Au in 10 mM CuSO4 / 0.1 M H2SO4
-200
-100
0
100
j /(µ
A/c
m²)
0.50.40.30.20.10.0
E /V
Cu UPDCu bulk
Cu bulk deposition vs. Cu underpotential deposition (UPD)
0.40.30.2E
/V
-25
0
j /(m
A/c
m²)
-100
-50
0
ΔT
/a. u
.
-0.2
0.0
E /V
100806040200t /ms
-25
0
j /(m
A/c
m²)
80604020
0ΔT
/a. u
.
Same net reaction Cu2+ + 2e- → Cu !?
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
8 Rolf Schuster
0.3Cu2+ + 0.3SO42- →
0.3Cu2+ad + 0.3 SO4
2-ad
Compatible with:Sabs(Cu2+) ≈ -128 J/KmolSabs(SO4
2-) ≈ 1 J/Kmol
Cu depositon on Cu bulk
Cu UPD formation
Microscopic processes
Cu2+ + 2e- → Cu
reve
rsib
lehe
at (µ
J/cm
2 )(c
orre
cted
for o
verp
oten
tial)
-25
-20
-15
-10
-5
0
-400 -300 -200 -100 0
conversion /(µC/cm²)
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0ML of Cu(111)
heat, due to
heat, due to anion coadsorption:
ΔRS helps in identifying reaction pathways and side reactions!
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
9 Rolf Schuster
First test experiments on charging/discharging LiCoO2
in cooperation with Heino Sommer and Petr Novák, Paul Scherrer Institut
-15
-10
-5
0
5
10
15
curre
nt d
ensi
ty /
mA
cm
-2
2.01.51.00.50.0
Potential vs. Pt / V
scan rate: 5 mV/s
charging: LiCo(III)O2 → ‚Co(IV)O2‘ + Li+ + e-
discharging: ‚Co(IV)O2‘+ Li+ + e- → LiCo(III)O2
LiCoO2 in dimethyl-carbonate /ethylene-carbonate, LiPF6
1 2 3
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
10 Rolf Schuster
0.300.280.26E
[V]
100x10-3806040200t [s]
-0.20-0.100.00
I [m
A]
-15-10-505
ΔT
[arb
. uni
ts]
0.340.32E
[V]
100x10-3806040200t [s]
0.15
0.00I [m
A]
302010
0
ΔT
[arb
. uni
ts]
Charging and discharging of slightly charged LiCoO2
We measure reversible heat effects, i.e., ΔRS
conversion ca. 2·1013 e-/cm2
(c.f., a Au(111) surface has 1.4·1015 atoms/cm2)
in cooperation with Heino Sommer and Petr Novák, Paul Scherrer Institut
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
11 Rolf Schuster
40
30
20
10
0
-10heat
/ co
nver
sion
[kJ/
eq]
0.30.20.10.0-0.1-0.2
pulse amplitude [V]
COLD
COLD
WARM
WARM
Φ = 0.3V, slightly charged
Φ = 0.5V, moderately chargedΦ = 1V, strongly charged
in cooperation with Heino Sommer and Petr Novák, Paul Scherrer Institut
- We can measure heat effects and determine the reversible heat, i.e., ΔRS.- Charging, i.e., Li+ formation leads to warming, i.e., ΔRS < 0.- The heat per equivalent dependens on the state of charge of the electrode - ΔRS < 0 !? Explicable by:
stong solvation of Li+ in dimethyl-carbonate /ethylene-carbonate (?)or side reactions (decomposition of LiCoO2, coadsorption prosesses,…)
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Institute of Physical Chemistry,
Physical Chemistry of Condensed Matter
12 Rolf Schuster
Future work on Li-ion batteries
- ΔRS for different states of charge of the electrode
- relyable calibration
- ΔRS for Li+ + e- → Li on Li-electrodes, dependence on the electrolyte
- effect of charging and discharging cycles on ΔRS
- ‚ideas‘ on elementary steps of the charging/discharging process
- ΔRS for Li+ + e- → Li upon intercalation of graphite / formation of the SEI