State of the Art of Batteries of the 4th
Generation
N. Wagner, N.A. Cañas, D. Wittmaier and K.A. FriedrichGerman Aerospace Center, Institute for Engineering
Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
8th International Workshop on Impedance Spectroscopy (IWIS)23-25 September, Chemnitz, Germany
Presentation outline
• Introduction and motivation• Definition 4th generation batteries• Examples of batteries and applications
• Metal-Sulfur Batteries• Li-Sulfur and Mg-Sulfur Batteries• Production technique• Characterization
• Metal-Air Batteries• Li-Air and Zn-Air Batteries• Production techniques at the DLR• Characterization
• Outlook
8th IWIS 2015, Norbert Wagner
Novel Battery Concepts – Specific Energy Potentials
Li-Ionhigh E
Pb Li-Ionhigh P
Li/S Li-air
10 100 1000 10000
gasoline(50 % of theoretical max.)
10 100 1 000 10 000Specific Energy / Wh/kg
Y. Mikhaylik et al., Sion Power Corp., ECS presentation, 2009.
USABC targetsLi/S (2009)
Rate Cap.
Lower T
Power Density
Specific Power
Recharge Time
Specific Energy
Energy density
Upper T
Cycle life
Chemistry Cell size Wh/L *theory
Wh/L actual
% achieved
Wh/kg *theory
Wh/kg actual
% achieved
LiFePO4 54208 1980 292 14.8 587 156 26.6LiFePO4 16650 1980 223 11.3 587 113 19.3LiMn2O4 26700 2060 296 14.4 500 109 21.8LiCoO2 18650 2950 570 19.3 1000 250 25
Si-LiMO2Panasonic 18650 2950 919 31.2 1000 252 25.2
8th IWIS 2015, Norbert Wagner
700
600
500
400
300
200
100
0
Spe
cific
Ene
rgy
@ c
ell l
evel
/ W
h kg
-1
203520302025202020152010
Year
150‐175 Wh/kg
175‐240 Wh/kg
> 350 Wh/kg
New SystemsLi‐S, Li‐Air andothers?
Limit of Li‐Ion Technology
Technical Progress: Improvement of Energy Density
Limit ?
Improvement jump
Lithium‐IonAdvanced activematerials
Lithium‐IonImproving existingChemistries
8th IWIS 2015, Norbert Wagner
Electrochemical pairs of Li-ion, post-Li ion and post-Li systems
Gravimetric energy density (Wh/kg)
Li-ion
Ca/CoF3
Chlorides
Mg/CuCl2
Ca/CuCl2
Li/CuCl2
Fluorides
La/CoF3
Ca/CoF3
Li/FeF3
Li/CuF2
LiC6 / NMC
Volu
met
ricen
ergy
dens
ity(W
h/l)
Mg batteries
MetalSulphur
Li/S
Mg/S
Metal-Air
Li/O2
Mg/O2
Zn/O2Na/O2
Na-ion
Hard-C / NaNMC
Li rich fcc materials
Li2VO2F
Li2CrO2F
Electropositive Electronegative
Chemistry of Fuel Cells and Batteries
2H2 + O2 2H2O
Hea
vy
Lig
ht
8th IWIS 2015, Norbert Wagner
Electropositive Electronegative
Chemistry of Fuel Cells and Batteries
2H2 + O2 2H2O2Li + O2 Li2O (Li2O2), LiOH
Hea
vy
Lig
ht
8th IWIS 2015, Norbert Wagner
Electropositive Electronegative
Chemistry of Fuel Cells and Batteries
2H2 + O2 2H2O2Li + O2 Li2O (Li2O2), LiOH16Li + S8 8Li2S8Mg + S8 8MgS
Hea
vy
Lig
ht
8th IWIS 2015, Norbert Wagner
Production and Characterisationof cathodes forLithium-Sulfur andLithium-air batteries
Characterisation ofLi-ion batteries within-situ and ex-situ-methods
Activities of the „Batterietechnik“ team at DLR
Source: N AT U R E | VO L 5 0 7 | 6 M A R C H 2 0 1 4
8th IWIS 2015, Norbert Wagner
Metal-Sulfur Batteries: Overview
Electrochemical Reaction ΔG Voltage Capacity(Cathode)
Energy density
kJ/mol V mAh/g Wh/kg Wh/L
Mg + S ↔ MgS -341.8 1.771 1672 1684 3221
2Li + S ↔ Li2S -439.0 2.275 1672 2654 2856
2Na + 3S ↔ Na2S3 -405.2 2.100 558.4 791.7 1179
2Al + 3S ↔ Al2S3 -213.3 1.106 1672 1184 2676
Zn + S ↔ ZnS -201.3 1.043 1672 573.6 2162
CoO2 + LiC6 ↔ LiCoO2 + C6 -347.4 3.600 273.8 567.8 1901
8th IWIS 2015, Norbert Wagner
Metal-Sulfur Batterie- Summary
Electrochemical Reaction ΔG Voltage Capacity(Cathode)
Energy density
kJ/mol V mAh/g Wh/kg Wh/L
Mg + S ↔ MgS -341.8 1.771 1672 1684 3221
2Li + S ↔ Li2S -439.0 2.275 1672 2654 2856
2Na + 3S ↔ Na2S3 -405.2 2.100 558.4 791.7 1179
2Al + 3S ↔ Al2S3 -213.3 1.106 1672 1184 2676
Zn + S ↔ ZnS -201.3 1.043 1672 573.6 2162
CoO2 + LiC6 ↔ LiCoO2 + C6 -347.4 3.600 273.8 567.8 1901
8th IWIS 2015, Norbert Wagner
‐Formation of Lithium‐Sulfur Battery: Electrochemistrydes in lithium‐sulfur batteries
Polysulfides (Li2Sx) areintermediates in the transition
of S8 to S2-
- gradual dissolution ofsulfur form the cathode
- Self-discharge- Different voltage
plateaus
Y.-S. Su et al., Nature (2013)
Electrolyte: LiPF6 in TEGDME
Cathode production technique at DLR-TT
• Nozzle with extern mixing of air andsuspension
• Cathode mixture: Sulfur or Sulfur/Carbon composite, Carbon Black and PVDF (50:40:10, wt.%). Solvents: Ethanol and DMSO
Suspension–spray machine
Sprayedcathode
5 x 5 cm2
Wet powder spraying for electrode fabrication
1
2
3
Cathode composition50 wt.% Sulfur40 wt.% Carbon Black10 wt.% PVDF
Mixing/Milling
Mixing
Solvent +PVDF
Dissolver
S + CB
Suspension
Wet‐powderspraying Drying
Air‐atomizing external mixing nozzlecontrolled by a 3D axis robot
The axis with the nozzle moves in perpendicular direction (y) to thesubstrate holder
3 times
8th IWIS 2015, Norbert Wagner
8th IWIS 2015, Norbert Wagner
Mixing/Milling Coating Drying
Initial procedure (Cathode I)
Roll mixer‡ Suspension spray In vacuum oven
1) Mix of S, CB and PVDF
(5 rpm, t= 12 h)
2) Mix with solvents†
(5 rpm, t= 12 h)
− Internal mixing nozzle − Coating in one step − Heating plate under
substrate (100 °C)
80 °C (48 h)
New procedure (Cathode II)
Tumbling mixer‡ Suspension spray In vacuum oven
1) Mix of S and CB
(20 rpm, t= 24 h)
2) Dissolution of PVDF in
solvents† (magnet stirring)
3) Mix of S and CB with
dissolution (2)
(20 rpm, t = 24 h)
− External mixing nozzle − Coating in 3 steps or more − No heating plate − Drying between each
sprayed layer
Between sprayed layers,
60 °C (1.5-3 h)
At the end of coating:
60 °C (24 h)
In vacuum in the glove
box
†Solvents: Ethanol/DMSO (50:50 wt.%). ‡In both cases ceramic balls were added in the
mixing tank.
N.A. Cañas, A.L.P. Baltazar, M.A.P. Morais, T.O. Freitag, N. Wagner, K.A. Friedrich, Electrochim. Acta, 157 (2015) 351-358
Influence of cathode fabrication
Influence of cathode fabrication
0.2 C
Optimization of suspension spraying and mixing processes
• Improved dispersion of S particles
• Reduction of S particle size
Cathode I Cathode II
Electrolyte: 1M LiPF6 in TEGDME
0.2 C rate
8th IWIS 2015, Norbert Wagner
Influence of LiNO3 as co‐salt
N. A. Cañas, A. L.P. Baltazar, M.A.P. Morais, T.O. Freitag, N. Wagner, K.A. Friedrich. Electrochimica Acta 157 (2015) 351‐358
Capacity fading and coulombic efficiency is affected by the concentration of the co‐salt
Considering both the capacity fading and the Coloumbic efficiency: the optimal concentration of LiNO3 was found to be 0.75M for this cell configuration/components
Electrolyte= 1M LiPF6 in TEGDME
~100% Coulombic efficiency
8th IWIS 2015, Norbert Wagner
Main in situ and ex situ characterization techniques
0 250 500 750 1000 1250 15000
250
500
750
1000
1250
1500
0 20 40 60 800
20
40
R0 R1//CPE1
R4//CPE4
R3//CPE3
Experimental Fitted
-Z'' /
Ohm
Z' / Ohm
R2//CPE2
60 mHz325 mHz
18 Hz
9 KHz
8th IWIS 2015, Norbert Wagner
20
Objective:• Monitoring of crystalline reaction products of the
cathode• identification of structural changes during cycling
In situ X-Ray diffraction
X-ray radiant tube
VÅNTECdetector
PotentiostatCycling program(Thales)
In-situ cell
1) anode plate2) polymer gasket3) insulator plastic tube4) spring5) stainless steel anode collector6) anode7) separator8) cathode9) cathode plate10) Al-window 11) holes for connecting the banana jacks
N. A. Cañas, S. Wolf, N. Wagner, K. A. Friedrich. J. of Power Sources, 226 (2013) 313‐319.
8th IWIS 2015, Norbert Wagner
21
Spectra collected during discharge
In situ X-Ray diffraction
0 20 40 60 80 100
1.6
2.0
2.4
2.8
20 22 24 26 28 30 32 34 36
0
100
200
300
400
100
80
60
40
20Polys
ulfid
es
- c -- b -- a -
Inte
nsity
/ a.
u
- c -
- b -
- a -
2-theta / °
DOD
/ %
111 (Li2S) 200 (Li2S)
222 (S8)
Vol
tage
/ V
DOD / %
0 10 20 30 40 50 60 70 80 90 1000.0
0.1
0.2
0.3
0.4111 - Li2S
Inte
g. in
tens
ity /
a.u.
Depth of discharge / %
222 - S8
(a)
(b)
0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
1500
Am
orph
ous
area
/ a.
u
Depth of discharge / %
1st discharge
a) Dissolution of sulfur and reduction to soluble polysulfidesb) Soluble polysulfidesc) Li2S formation
N. A. Cañas, S. Wolf, N. Wagner, K. A. Friedrich. J. of Power Sources, 226 (2013) 313‐319.
Quantification of crystalline and amorphous phase
8th IWIS 2015, Norbert Wagner
UV‐vis spectroscopy
References:a) Stoichiometric mixture of Li2S and S8 in TEGDME* b) Li2S in TEGDMEc) S8 in TEGDME
Experimental set‐up
Wavelength /nm
Species (in TEGDME)
245,255, 282 S− (Li2S)
243, 265, 289 cyclo S8
332 S62−
425 S42−
615 S3•−
N. A. Cañas, D. N. Fronczek, N. Wagner, A. Latz, K. A. Friedrich. J. Phys. Chem. C, 2014, 118, 12106–12114.
*TEGDME:Tetraethylene glycol dimethyl ether
Investigation and quantification of reaction intermediates (polysulfides)
8th IWIS 2015, Norbert Wagner
Electrochemical Impedance spectroscopy (EIS)
Investigation of physical and chemical processes during cycling
0 250 500 750 1000 1250 15000
250
500
750
1000
1250
1500
0 20 40 60 800
20
40
R0 R1//CPE1
R4//CPE4
R3//CPE3
Experimental Fitted
-Z''
/ Ohm
Z' / Ohm
R2//CPE2
60 mHz325 mHz
18 Hz
9 KHz
Assignment of processes to the elements of the EC
Model Chemical and physical cause
R0 Ohmic resistance
R1-CPE1 Anode charge transfer
R2-CPE2 Cathode process: charge transfer of sulfur intermediates
R3-CPE3 Cathode process: reaction and formation of S8 and Li2S
R4-CPE4 Diffusion
N. A. Cañas, K. Hirose, B. Pascucci, N. Wagner K. A. Friedrich, R. Hiesgen, Electrochim. Acta, 2013, 97, 42–51.
8th IWIS 2015, Norbert Wagner
ElS during 1st discharging cycle
0 20 40 60 80 1000
500
1000
1500
2000
2500
3000
200004000060000
R3
R4
R3,
R4 /
Ohm
Depth of discharge / %
??
0
20
40
60
80
100 R0
R1
R0,
R1 /
Ohm
0
250
500
750
1000
1250
1500
1750
2000
R2 /
Ohm
(a)
(b)
(c)
0 20 40 60 80 1001.0
1.5
2.0
2.5
3.0
Pot
entia
l / V
Depth of discharge / %
Discharge curve EIS measurements
0 250 500 750 1000 1250 15000
250
500
750
1000
1250
1500
0 25 50 750
25
50 DOD / % 0 27 34 62 81100
-Z'' /
Ohm
Z' / Ohm
-Z'' /
Ohm
Z' / Ohm
R0: Increase of resistance due to dissolution of Li2SxR1: Anodic charage transfer resistance influenced by Li2SxR2: Cathodic charge transfer resistance diminishes with order or polysulfide
R3: Proportional to formation of isolating products (Li2S and S8)
R4: Diffusion hindered by formation of Li2S and S8
8th IWIS 2015, Norbert Wagner
Variation of the equivalent circuit elements during first charging determined by EIS analysis
8th IWIS 2015, Norbert Wagner
Strong discharge
capacity fading
Decrease of cathodic charge
transfer (R2)
No complete conversion to Li2S
ElS during 50 charging/ discharging cycle
New batteries concepts Further cathode improvements
Components
• Electrolyte/sulfur weight ratio: ≤ 3/1
• Mass loading higher than 2 mg cm−2
• Sulfur utilization ≥ 70 %
Different approaches or combination of them:
• Additives: hydrophilic inorganic additives (like MexOy) for adsorption of polysulfides
• Protective layers: ion conductive interlayers for retention of active material
• Binders: replacement of conventional PVDF by ion /electric conductive additive
Guideline for an optimized electrode and cell design:
• Modeling from a single active particle to full battery cells
• Mechanistic studies of degradation processes on both electrodes
8th IWIS 2015, Norbert Wagner
Main companies developing Li/S Batteries in industry
Oxis Energy:• 300 Wh/kg achieved at cell level in 2014• 400 Wh/kg forecast in 2016
http://www.oxisenergy.com/technology/http://www.sionpower.com/http://www.polyplus.com/
Sion Power:• 250 Wh/kg and over 300 full depth of discharge cycles (now)• 600 Wh/kg are in the foreseeable future
Berkeley, USA Tucson, USA Abingdon, UK
Target for commercialization: ca. 500 Wh/kg
8th IWIS 2015, Norbert Wagner
Mg2+
e-
e-
Anode Cathode
discharge
charge
Mg
Good handling and operational safety
No dendrite formation using Mg metal as anode
Naturally abundant low raw material cost (currently Li/25)
Mg/S offers theoretical 4000 Wh/L while the gravimetric capacity is similar to that of LiC6
Sulfur cathode needs non-nucleophilic electrolyte
Li MgAtomic weight 6.9 24.3
Ionic radius 90 pm 86 pm
Ionic charge + 1 + 2
Reduction potential - 3.04 V - 2.37 V
Density 0.53 g/cm3 1.74 g/cm3
Gravimetric capacity 3861 mAh/g 2205 mAh/g
Volumetric capacity 2061 mAh/cm3 3832 mAh/cm3
Li-Sulfur vs. Mg-Sulfur Battery
smaller S22-
would not dissolve !
Approach to eliminate formation of soluble polysulphides
Ultramicroporous carbonmade from coconut shells (inexpensive, scalable).Pore ø 0.6 nm
S8 and soluble S82-
do not fit in pore
Hypothesis:direct transition of S to Li2S2 and Li2S
one reaction step one plateau
50 mass% S loading
e-
e-
Li+No access toelectrolyte
Reduction of polysulfide shuttle
Coconut shell
Poro
us c
arbo
n
Carbon-Sulphurcomposite
Coconut Shell derived CarbonCoconut Shell derived Carbon-Sulphur composite
CSCCSC-S
Synthesis of Coconut Shell derived Carbon-Sulphur (CSC-S) composite
Li W., Yang K., Peng, J. Zhang, Guo, S., Xia, H. Ind. Crop. Prod. 28, 190–198 (2008).
Production of Carbon‐Sulfur Composite 8th IWIS 2015, Norbert Wagner
MotivationWhy Li-air batteries?• Highest theoretical specific energy density (11.425 Wh/kg)
Cathodic reactant, O2 from air, does not have to be stored• Environmental friendliness• Higher safety than Li-ion batteries
(only one of the reactants contained in the battery)• Potentially longer cycle and shelf lives
8th IWIS 2015, Norbert Wagner
Motivation
G. Girishkumar et al., J. Phys. Chem. Lett.,2010, 1, 2193‐2203
Why Li-air batteries?• Highest theoretical specific energy density (11.425 Wh/kg).
Cathodic reactant, O2 from air, does not have to be stored• Environmental friendliness• Higher safety than Li-ion batteries
(only one of the reactants contained in the battery)• Potentially longer cycle and shelf lives
8th IWIS 2015, Norbert Wagner
Li‐air battery:Functional scheme
MetallicLithium
Separator
GasDiffusionElectrode
O2
Electrolyte
LiOH
LiOH
=Lithium‐IonLi+=OxygenO2=Electron e‐=Hydroxide‐IonOH‐
Structure:• Anode,Lithiummetal (foil)• Cathode (Gasdiffusion electrode =GDE)• Separator
Reactions and products:• During discharge:OxygenReduction Reaction
(ORR)• During charging:OxygenEvolutionReaction (OER)• Reaction product:
• organic electrolyte:Li2O,Li2O2• alkaline electrolyte:LiOH
DLR:• Bifunctional Cathode (GDE)with alkaline
electrolyte (LiOH)• Globalreaction:4Li+O2 +2H2O↔4LiOH;
E=3.45V
IWIS 2015, Norbert Wagner
Architectures of Li-air Batteries
2Li+ + O2 + 2e‐ Li2O2 Erev= 2,959 V2Li++2e‐ + (1/2) O2 Li2O Erev= 2,913 V
4Li + O2 + 2H2O 4LiOH (alkaline media) Erev= 3,446 V4Li + O2 + 4H+ 2H2O + 4Li+(acidic media) Erev= 4,274 V
Non-aqueous electrolyte: Aqueous electrolyte:
8th IWIS 2015, Norbert Wagner
Bi-functional Oxygen-Electrodes: Design
• Bi-functional Oxygen-Electrodes = catalizes ORR and OER
• Depending on manufactoring process every electrode consists of:
• Catalyst(s)• Conductive agent (C, Graphit…)• Binder (PTFE, PVdF…)• Substrate (Metal mesh,…)
Function BOE
Catalyst
Active Surface
Cond. agent
Electrolyte
Pore-structure
Design
• Different manufactoring processes used at DLR: Dry Powder Spraying, Reactive Rolling an Mixing, Pressing and APS
Manufactoring of bifunctional gas diffusion electrodes
Electrodes with noble metal and other catalysts can be made with dry power spraying technique
Oxide catalysts (La0.6Ca0.4CoO3…) can be sprayed on for example a
Rhodius substrate with APS
Rhodius substrate
Catalyst layer
Catalyst layer = catalyst+carbon/grap
hite+binder
Graphite GDE substrate
or by pressing the catalyst layer on for example a Sigracet® GDL 35 DC with a hydraulic press
Catalyst layer = catalyst+carbon/grap
hite+binder
Sigracet® GDL35 DC
8th IWIS 2015, Norbert Wagner
Screening of bifunctional catalystsExperimental
• Thin catalyst layers reduce the influence of the electrode structure
• Cyclic Voltammetrie was carried out at a half cell with 1M LiOH (aq.) and25°C and 50°C
• Gas O2, platinum counter electrode (CE), reversible hydrogen reference electrode (RE)
Potential range 0.1V - 1.8V vs. RHE
8th IWIS 2015, Norbert Wagner
Bi-functional Oxygen-Electrodes: IrO2/- and Co3O4/Ag-electrodes
• CV´s electrodes 20 wt. % catalyst (IrO2, Co3O4
• Improved cyclingperformance due touse of IrO2 and Co3O4compared to pure Ag
0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0-150
-100
-50
0
50
100
Cu
rren
t d
ensi
ty [
mA
cm
-2]
Voltage vs. RHE [V]
Co3O
4/Ag
IrO2/Ag
Ag
No IR corr.
max. overpotential 1.5V
2.6V vs. Li/Li+
Current density @ 2.6V vs. Li/Li+ [mA cm-2]
IrO2/Ag 99,7Co3O4/Ag 107
N. Wagner , D. Wittmaier, German Patent Application, 2014
Overview EIS measurement points and CV with 1 mV/s at RT, 1 N LiOH , Ag-GDE
-0,3
-0,25
-0,2
-0,15
-0,1
-0,05
0
0,05
0,1
0,15
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2
Cur
rent
den
sity
/ A
cm
-2
Potential vs. RHE / V
Electrode 1 (high pressure) 25c
Electrode 1 (high pressure) 50c
Electrode 2 (high pressure) 25c
Electrode 2 (low pressure) 50c
EIS measurement point
Electrode 1 (high pressure) 25°C
Electrode 1 (high pressure) 50°C
Electrode 2 (low pressure) 25°C
Electrode 2 (low pressure) 50°C
8th IWIS 2015, Norbert Wagner
Impedance measurements during Oxygen evolutionon Ag-GDE (high pressure), 1 N LiOH, 25°C
1 100 10K
5
10
20
15
50
|Z| /
0
15
30
45
60
75
90
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se| /
o
frequency / Hz
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OCV+100 mV
OCV+300 mV
OCV+500 mVOCV+700 mV
10 20 30 40 50
0
-30
-20
-10
10
Z' /
Z'' /
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bbbbb
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OCV+100 mV
OCV+300 mVOCV+500 mV
OCV+700 mV
8th IWIS 2015, Norbert Wagner
Equivalent circuit used for evaluation of EIS during OCR and OER at different electrodes for Lithium-Air batteries
8th IWIS 2015, Norbert Wagner
mZZe
Current collector GDL
electrolyte pores
porous layer
Zs1 ZsnZsi
ZpnZpiZp1
Z q1 Zqi Zqn
H. Göhr in Electrochemical Applications/97, www.zahner.de
Cylindrical homogeneous porous electrode model (H. Göhr)
Ions (H+, OH -,..)
I I
Por
e
Ele
ctro
de, p
orou
s lay
er
Electrolyte Zq
Zp ZS
Zo
Zn
Current (e-)
8th IWIS 2015, Norbert Wagner
Potential dependency of total resistance duringORR at different electrodes, 1 N LiOH
1
10
100
0 200 400 600 800 1000
Res
ista
nce
/ Ω
Potential OCV minus x / mV
Electrode 1 (high pressure) 25cElectrode 1 (high pressure) 50cElectrode 2 (low pressure) 25cElectrode 2 (low pressure) 50c
Rtotal ORR
8th IWIS 2015, Norbert Wagner
Potential dependency of charge transferresistance during OER
0,01
0,1
1
10
100
100 200 300 400 500 600 700 800
Res
ista
nce
/ Ω
Potential OCV plus x / mV
Electrode 1 (high pressure) 25cElectrode 1 (high pressure) 50cElectrode 2 (high pressure) 25cElectrode 2 (low pressure) 50c
R2 OER (charge transfer)
8th IWIS 2015, Norbert Wagner
Potential dependency of charge transferresistance in oxide layer potential region (OER)
0
0,5
1
1,5
2
2,5
3
3,5
4
100 200 300 400 500 600 700 800
Res
ista
nce
/ Ω
Potential OCV plus x / mV
Electrode 1 (high pressure) 25c
Electrode 1 (high pressure) 50c
Electrode 2 (high pressure) 25c
Electrode 2 (low pressure) 50c
R5 OER (oxide layer)
8th IWIS 2015, Norbert Wagner