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Shannon Boettcher – Electrochemical Energy Storage 1
Electrochemical Energy Storage: Design Principles for Oxygen Electrocatalysts
and Aqueous Supercapacitors
Shannon W. Boettcher Asst. Prof. of Chemistry University of Oregon Eugene, USA
Boettcher Solar Materials and Electrochemistry Laboratory
Motivation: Powering the planet
Solar is the only renewable source capable of providing 20-50 TW of power worldwide.
3 TW
*Lewis, MRS Bulletin, (32) 808 2007.
Wind < 4 TW Biomass < 5 TW Hydro < 1.5 TW Geothermal < 1 TW Solar ~ 120,000 TW
Worldwide potential*:
Global power consumption: ~18 TW
Shannon Boettcher – Electrochemical Energy Storage 2
Shannon Boettcher – Electrochemical Energy Storage 3
Cost of solar energy must be reduced. We must store that energy.
Solar Electricity > 11 ¢ per kWh (sunny climate, large installation) Industrial Electricity ~ 5-10 ¢ per kWh
Solar Energy Challenges
Shannon Boettcher – Electrochemical Energy Storage 4
Solar Materials and Electrochemistry Lab solar fuels electrochemical capacitors
scalable III-V semiconductors for PV
2H2O O2
O Ni ?
OER active site design?
interface theory
aq. low-T synthesis of functional films precise precursors
Fe
Shannon Boettcher – Electrochemical Energy Storage 5
Solar fuels synthesis using semiconductors and electrocatalysts
solution n-type SC
solution p-type SC
Walter, M.; Warren, E.; McKone, J.; Boettcher, S. W.; Qixi, M.; Santori, L.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446-6473.
Shannon Boettcher – Electrochemical Energy Storage 6
Oxygen electrocatalysis has broad importance
solar water splitting
air-breathing batteries
fuel-cells (ORR)
http://protononsite.com/
large scale electrolysis
Shannon Boettcher – Electrochemical Energy Storage 7
From Wang et al., Electrochimica Acta, 2005, 50, 2059–2064
Need for well-defined systems and clean measurements
Smith, R.D.L. et al. Science, 2013, 340, 60.
Designed for maximum current per geometric area Dark colored – poorly suited for integrating in solar fuels systems
What is the role of composition, conductivity, and porosity? What is the surface-active component? Complicated!
O2
h+
Shannon Boettcher – Electrochemical Energy Storage 8
How do we design well-defined catalysts? What determines their activity?
Kerisha Williams
James Ranney
(Dr.) Lena Trotochaud
Team Catalyst c. 2011
Shannon Boettcher – Electrochemical Energy Storage 9
Solution-processed ultra-thin film catalysts
Advantages for fundamental study:
• Catalyst electrical conductivity (largely) irrelevant • Film composition controlled
exactly by precursor solution • Mass known • Surface area controlled • Facile gas and ion transport
~50 wt% surfactant ~ 0.05 M metal nitrate ethanol
spin-casting
E-QCM
Trotochaud, L.; Ranney, J.K.; Williams, K.N.; Boettcher, S.W. J. Am. Chem. Soc., 2012, 134, 17253.
100 nm NiOx
= Film
E-QCM
Shannon Boettcher – Electrochemical Energy Storage 10
Initial target: Ni-Co-O
1. Trasatti, S.; Lodi, G. In Electrodes of Conductive Metallic Oxides; Trasatti, S., Ed.; Elsevier: Amsterdam, 1981; Vol. B, p 521-626. 2. Rasiyah, P.; Tseung, A. C. C. A mechanistic study of oxygen evolution on NiCo2O4 J. Electrochem.Soc. 1983, 130,2384-2386.
Mixing Co and Ni oxides reported = better performance. electronic? chemical? morphological?
* Indicates bonded to the surface H2O → *OH → *O + H2O → *OOH → O2
* Indicates bonded to the surface (see Rossmeisl, Norskov, etc.)
Shannon Boettcher – Electrochemical Energy Storage 11
Oxygen evolution with NixCo1-xOy films
1Rasiyah, P.; Tseung, A. C. C. A mechanistic study of oxygen evolution on NiCo2O4 J. Electrochem.Soc. 1983, 130,2384-2386.
Performance increases with increasing Ni content. No synergistic effect apparent. Apparent activity of “plain NiO” very high. Why?
- steady-state (> 15-30 min/step), 1 M KOH (99.999%) -Hg|HgO 1 M KOH reference (0.929 V vs. RHE at pH 14 or 0.112 V vs. NHE) - Rs 2-3 Ω via AC impedance
NiCo2O4 20 μm film,1 pH 14
Teff = 2-3 nm Performance increases with increasing Ni content. No synergistic effect apparent. Apparent activity of “plain NiO” very high. Why?
Shannon Boettcher – Electrochemical Energy Storage 12
Samples containing NiO evolve as a function of time
in-situ formation of a NiOOH?
?
Corrigan, D. A.; Bendert,. J. Electrochem. Soc. 1988, 135, C156-C156.
NiOx
1M 99.999% KOH, 20 mV s-1
0.3 V vs. Hg|HgO
Shannon Boettcher – Electrochemical Energy Storage 13
XPS analysis confirms transition to Ni(OH)2/NiOOH
Grosvenor, A. P.; Biesinger, M. C.; Smart, R. S.; McIntyre, N. S. New interpretations of XPS spectra of nickel metal and oxides. Surf. Sci. 2006, 600, 1771-1779.
O 1s Ni 2p
NiO
Ni(OH)2 Ni2O3
NiO
Shannon Boettcher – Electrochemical Energy Storage 14
Co substitution suppresses transformation to oxyhydroxide
1M 99.999% KOH, 20 mV s-1
Alloying with Co suppresses formation of Ni(OH)2 / NiOOH during conditioning.
sample e- per metal e- per Ni CoOx 0.04 n/a
Ni0.25Co0.75Ox 0.07 0.27 Ni0.5Co0.5Ox 0.31 0.63
Ni0.75Co0.25Ox 0.61 0.82 NiOx 1.0 1.0
CV curves collected after 6 hr conditioning: # Ni measured with QCM
Shannon Boettcher – Electrochemical Energy Storage 15
In-situ phase transformation
Rock Salt (NiO) catalysis limited to surface
Brucite/Hydrotalcite (e.g. M(OH)2/MOOH) catalysis throughout bulk – “3D”
Spinel (e.g. Co3O4) catalysis limited to surface
X
Active structure:
Shannon Boettcher – Electrochemical Energy Storage 16
Ni(OH)2 electrochemistry studied extensively for alkaline batteries
Corrigan, D.A. J. Electrochem. Soc. 1987, 134, 377. Corrigan, D.A.; Bendert, R.M. J. Electrochem. Soc. 1989, 136, 723.
Fe is incorporated into electrochemically conditioned
NiOOH films
Dennis Corrigan: – Ni(OH)2 films cathodically
electrodeposited • Fe increases OER activity
– Fe added intentionally – or Fe impurities in
electrolyte
Electrochemically Conditioned Sample
EPMA Fe/(Ni+Co)
XPS Fe/(Ni+Co)
CoOx 0 0 Ni0.5Co0.5Ox 0.034 0.11
NiOx 0.18 0.14 NiOx, electrolyzed
KOH 0.035 0.079
Shannon Boettcher – Electrochemical Energy Storage 17
Thin-film OER catalyst quantitative comparison using an EQCM
sample
η @ J = 1 mA cm-2
(mV)
Tafel Slope (mV
dec-1) A g-1 TOF
(sec-1)
MnOx 512 49 ± 3 1.3 0.0003
FeOx 409 51 ± 3 4.5 0.0009
CoOx 395 49 ± 1 7.6 0.0016
IrOx 381 42 ± 1 24.2 0.014 (Fe)
Ni0.5Co0.5Ox 321 35 ± 2 273 0.056
NiOx (Fe) 300 29 ± 0.4 773 0.17
Fe0.1Ni0.9 Ox 297 30 ± 1 1009 0.21
at η = 300 mV
• Fe:NiOOH >10x more active an IrO2 and >100x more active than CoOx • Highest activity OER known in basic media. Why???
TOF = # O2 produced per metal per second
Trotochaud, L.; Ranney, J.K.; Williams, K.N.; Boettcher, S.W. J. Am. Chem. Soc., 2012, 134, 17253. Corrigan, D.A. J. Electrochem. Soc. 1987, 134, 377.
E-QCM
2 nm film: 10 mA cm-2 η = 336 mV
The role of Fe in NiOOH
• Crystal structure and (dis)order? • “Energetics” of electronic states, i.e. “d-band” position? • Film electronic conductivity?
Smith, R.D.L. et al. Science, 2013, 340, 60. Smith, R.D.L. et al. J. Am. Chem. Soc. 2013, 135, 11580. Corrigan, D.A. J. Electrochem Soc., 1987, 134, 377. Corrigan, D.A.; Bendert, R.M. J. Electrochem. Soc. 1989, 136, 723.
Louie, M.W.; Bell, A.T. J. Am. Chem. Soc., 2013, 135, 12329.
Active site between the
sheets?
Shannon Boettcher – Electrochemical Energy Storage 18
E(Ni2+/3+)
shifts with [Fe]
Minimizing Fe Impurities
Corrigan, D.A. J. Electrochem Soc., 1987, 134, 377. Trotochaud, L.; Young, S.L.; Ranney, J.K.; Boettcher, S.W. Submitted.
Activity increase with each cycle
Glassy C (GC) rotating disk electrode Teflon cell, TraceSelect KOH (< 36 ppb Fe) 99.999% Ni(NO3)2·6H2O
1500 rpm
No applied potential required for Fe incorporation
X-ray photoelectron spectroscopy Need to use Mg X-ray source
Shannon Boettcher – Electrochemical Energy Storage 19
Electrolyte Purification
• Precipitate Ni(OH)2 – TraceSelect KOH and 99.999% Ni(NO3)2·6H2O
• Wash/centrifuge/decant • Add electrolyte and shake…
No Fe after 300 CV cycles
Trotochaud, L.; Young, S.L.; Ranney, J.K.; Boettcher, S.W. J. Am. Chem. Soc. 2014.
Shannon Boettcher – Electrochemical Energy Storage 20
Role of 3D structure?
from Godwin, I.J.; Lyons, M.E.G. Electrochem. Commun. 2013, 32, 39. Louie, M.W.; Bell, A.T. J. Am. Chem. Soc., 2013, 135, 12329.
Is β-NiOOH actually more active? Previous reports contain Fe?
α/γ β/β
Shannon Boettcher – Electrochemical Energy Storage 21
“Crystallized” Ni(Fe)OOH
Trotochaud, L.; Young, S.L.; Ranney, J.K.; Boettcher, S.W. Submitted.
Shannon Boettcher – Electrochemical Energy Storage 22 Trotochaud, Young, Ranney, Boettcher, S.W. J. Am. Chem. Soc. 2014.
Peaks shift with crystallization of β-NiOH2 - activity increases
No significant change in OER activity with crystallization
aged in 40 °C 1M KOH, CV 10 mV s-1 every 5 min
Fe-Free NiOOH after crystallization
Trotochaud, L.; Young, S.L.; Ranney, J.K.; Boettcher, S.W. Submitted.
activity decreases
• New peak formation – minimal peak shift • No increase in activity • NiOOH very poor OER catalyst without Fe
Shannon Boettcher – Electrochemical Energy Storage 23
Aging and crystallinity
• Aging increases long-range order • Fe co-deposition gives larger inter-sheet spacing
Order and sheet spacing apparently not (strongly) related to activity.
Shannon Boettcher – Electrochemical Energy Storage 24
Does Fe change electronic conductivity under OER conditions?
Trotochaud, L.; Young, S.L.; Ranney, J.K.; Boettcher, S.W. Submitted.
Not important mechanism for activity enhancement
VNldwIcond
∆=σ
For 100 nm NiOOH film at 10 mA cm-2,
<1 mV drop
# electrodes electrode length
film thickness
gap spacing
bare
Shannon Boettcher – Electrochemical Energy Storage 25
2 μm
Other mixed metal oxyhydroxides?
Shannon Boettcher – Electrochemical Energy Storage 26 Michaela Burke
(Fe)CoOOH
Burke, Kast, Trotochaud, Boettcher, near submission to JACS 2014.
OER onset near conductivity onset for FeOOH
Fe = %
FeOOH (Fe)CoOOH
CoOOH
OER mechanism in (oxy)hydroxides
• NiOOH bad OER catalyst – low activity • FeOOH has low conductivity thus low apparent activity • Fe active site likely; modulated by NiOOH / CoOOH
electrically conductive “porous” framework
Shannon Boettcher – Electrochemical Energy Storage 27
O2 4OH-
O Ni or Co
Fe OH
* See also recent theory / XAS from Norskov, Bell
• Conductive NiOOH/CoOOH = strongly coupled cations; delocalized electrons
A revised volcano plot
Shannon Boettcher – Electrochemical Energy Storage 28
Previous Trend: Ni > Co > Fe > Mn “oxophilicity” of cation
Real Trend: NiFe > CoFe > Fe > Co > Ni Exact opposite
Subbaraman and Markovic, et. al. Nat. Mater. 2012, 11, 550.
Michaela Burke Lisa Enman
Chris Gabor Adam Batchellor Qui Hui Jacyln Kellon
- Design better catalysts - Integration with AEM
Shannon Boettcher – Electrochemical Energy Storage
Semiconductor-catalyst interfaces
Lin, Boettcher, Nature Mater. 13 (1), 81, 2014.
light
Φb
Φb,eff
different Jo,cat
ener
gy
position Mills, Lin, Boettcher Phys. Rev. Lett. 112, 148304, 2014.
T.J. Mills Fuding Lin
29
Shannon Boettcher – Electrochemical Energy Storage 30
Part II: Redox-enhanced electrochemical double layer
capacitors
Sangeun Chun
Galen Stucky Brian Evanko David Ji
Xingfeng Wang
Shannon Boettcher – Electrochemical Energy Storage 31
Traditional electrochemical double-layer capacitors
Pros: power, cycle-ability Cons: carbon cost, flammable electrolyte, low specific/volumetric energy
Simon, Gogotsi, Nat Mater 2008, 7, 845.
www.maxwell.com
+ − + −
+ − + − + − + − + − + − − +
target
electrolyte
energy = 1/2CV2
Shannon Boettcher – Electrochemical Energy Storage 32
• Merits (vs. EDLC) − electrolyte weight as active component − increased capacity / specific energy − use of aqueous electrolytes with high solubility (limited by low V) • Challenges − self-discharge − maintain cycleability and high power
separator
current collector
+ −
Lu, Beguin, Frackowiak, Supercapacitor: Materials, Systems and Applications, Wiley, 2013
Concept: Redox-enhanced supercapacitor
Shannon Boettcher – Electrochemical Energy Storage 33
Redox electrolyte “design principles”
• use aqueous electrolyte (safety, cost) • need different redox processes at negative and positive electrodes • formal potentials near solvent window (energy) • high solubility (energy) • fast kinetics (power) • stable (cyclability) • design for slow self discharge??
separator
current collector
+ −
Lu, Beguin, Frackowiak, Supercapacitor: Materials, Systems and Applications, Wiley, 2013
Shannon Boettcher – Electrochemical Energy Storage 34
Potential redox couple species
MV = methyl viologen
Need: - high solubility - large ΔV btw. couples - fast kinetics - slow self discharge
Shannon Boettcher – Electrochemical Energy Storage 35
Three electrode cell design
Epoxy insulating layer
Glassy carbon (current collector)
Ni bar N2 purge
10 mg per electrode, ~220 um thick - Activated carbon prepared by standard
CO2 activation process - Electrode pellet - AC (85 %) : PTFE (10 %) : Acetylene black (5 wt.%)
Shannon Boettcher – Electrochemical Energy Storage 36
Control inert electrolyte
C = Q/V energy = 1/2CV2
Charging 1 A/g
Discharging −1 A/g
Shannon Boettcher – Electrochemical Energy Storage 37
Halogen electrolytes for positive electrode
Three electrode Swage-lock cell used to monitor both electrode processes simultaneously.
capacitive
faradaic
3I- → I3- + 2e- 3Br- → Br3- + 2e-
charging at 1 A/g
Shannon Boettcher – Electrochemical Energy Storage 38
Self-discharge dynamics
• I- and Br- show slow self-discharge rate (specific absorption) • Fe(CN)6
4-/Fe(CN)63- redox couple shows fast self-discharge
• Co(bpy)32+/Co(bpy)3
3+ extremely fast self-discharge (electrostatics)
3Br- → Br3
- + 2e-
* 1 M K2SO4
Weber et. al. J Appl Electrochem 41, 1137-1164 (2011).
Shannon Boettcher – Electrochemical Energy Storage 39
Redox electrolytes for positive electrode
MV = methyl viologen
• MV+ specific absorption slowing self-discharge?
Shannon Boettcher – Electrochemical Energy Storage 40
Combined redox electrolytes 1 M KBr/0.1 M MVCl2
• capacitive and faradaic responses evident on both electrodes • potentials separated by ~1.4 V – ideal in aq. electrolyte
Shannon Boettcher – Electrochemical Energy Storage 41
Combined redox electrolytes
• competitive over short times with non-aqueous cells
• replace methyl with heptyl – decreases self discharge dramatically
N+ N+2Br
-
HV2+
Shannon Boettcher – Electrochemical Energy Storage 42
Power – energy – stability
N+ N+
OO
OO
2Br-
enhanced stability and solubility:
Chun, S.; Evanko, B.; Wang, X.; Ji, X.; Stucky, G.D.; Boettcher, S.W. In prep for Nature Communications. 2014.
Shannon Boettcher – Electrochemical Energy Storage 43
Nernstian electrochemical model
Brian Evanko
• symmetric electrodes, no separator • agreement with experimental data • improved performance possible
*
Shannon Boettcher – Electrochemical Energy Storage 44
Summary: Redox Supercapactiors
Brian Evanko
Sangeun Chun
• redox-active electrolyte = additional capacity
• electrostatics and specific absorption critical to prevent internal shunting
• record performance of ~15 Wh kg-1 for aq. redox capacitor
• >2000 cycles with heptyl-viologen • useful niche between capacitor and
battery?
Shannon Boettcher – Electrochemical Energy Storage 45
Acknowledgements
Dr. Fuding Lin T.J. Mills
Theory and Simulation Interfaces
Basic Energy Sciences Solar Photochemistry
OER Catalysis:
Young Professor Program
CSVT GaAs PV: Redox Capacitors:
Thin Films:
Interfaces:
(Dr.) Lena Trotochaud
Oxygen Catalysis
Michaela Burke
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