operando ir and raman spectroscopy of the catalyst ionomer

Neili Loupea, Jonathan Doana, Ryan Crusea, Nicholas Dimakisb, Khaldoon Abu-Hakmehc, SeungSoon Jangc, William A Goddard IIId, Eugene S. Smotkina

a: Department of Chemistry and Chemical Biology b: Department of PhysicsNortheastern University University of Texas Rio Grande Valley Boston, MA 02115 Edinburg, TX [email protected]

c: School of Materials Science and Engineering d: Materials and Process Simulation CenterGeorgia Institute of Technology California Institute of TechnologyAtlanta, GA 30332 Pasadena, CA 91125

Operando IR and Raman Spectroscopy of the Catalyst Ionomer Interface

DOE Catalysis Working Group MeetingArgonne National Laboratory, Building 241/D172Wednesday, July 27. 2016

1

mailto:[email protected]

Overview

2

1. Operando spectroscopy fuel cells (IR, XAS, Raman)2. Why operando?

Structural changes during catalysis (XAS case study)3. IR spectroscopy of catalyst ionomer interface

Molecular orbital explanation of COads Stark tuningStark tuning: Probe for interfacial co-adsorption and electrocatalysis

4. IR spectroscopy in proximity to the catalyst/ionomer interfaceShort chain, 3M and Nafion membranes

Band assignments in terms of exchange site local symmetryC1 (sulfonic acid) and C3V (sulfonate) local symmetry modesHydration dependent distribution of per site λ (waters/exchange site).

Molecular dynamics modeling and state of hydration IR spectroscopy5. Fuel cell operando Raman spectroscopy (Case study: Non-PGM catalyst)

Membrane exchange site transition from C1 to C3V symmetry during ORRNo Stark tuning of Fe-O stretching modeCatalysis hypothesized as due to 14 ppm Pt contaminant

3

Operando IR and Raman spectroscopy

4

Operando direct methanol fuel cell X-ray absorption spectroscopy: A case study exemplifying the need for operando measurements.

-0.66

-0.64

-0.62

-0.6

-0.58

-0.56

21750 22250 22750 23250Energy, eV

Abs

orpt

ion

Expulsion of CO2 bubble

Formation of CO2 bubble.

CO2 phase-out was mitigated by application of a backpressure to the methanol anode.

S Stoupin et al. Pt and Ru X-ray Absorption Spectroscopy of PtRu Anode Catalysts in Operating Direct Methanol Fuel Cells J Phys Chem B, 110, 9932 -9938, (2006)

0.0

0.5

1.0

22080 22120 22160 22200Energy, eV

Nor

mal

ized

abs

orpt

ion

Ru oxide Ru oxide hydrate

Fresh JM

Ru metal (blue)

Ru in operating PtRuJM electrode (red)

Operando DMFC anode is always metallic

ACS San Francisco – September 14, 2006

Johnson Matthey PtRu (1:1) structural changes during catalysis

As received PtRu (1:1)

• Ru oxidation ~58%• N = 5.6• [Ru]/[Pt] = 0.44• Pt-O bonds present• Ru-O bonds ~2.8 avg

Operando PtRu (1:1)

• Ru oxidation ~15%• N = 8.2• [Ru]/[Pt] = 0.50• No Pt-O bonds• Ru-O bonds ~0.24 avg

S Stoupin et al., J.Phys Chem B, 110, 9932 (2006).

Vibrational Spectroscopy of the Pt/ionomer interface

6

I Kendrick et al. Elucidating the Ionomer-Electrified Metal Interface, J.Am. Chem. Soc., 132 (49), 17611–17616 (2010)

Co-adsorbates include sulfonate exchange site and the –CF3 group.

7

Stark Tuning: Potential dependent COads stretching frequencies.Higher electrode Fermi levels = Reduced CO stretching frequencies.

B. Hammer, O. H. Nielsen and J. K. Norskov, Catalysis Letters, 1997, 46, 31-35

Stark tuning: From model surfaces to fuel cell Pt/ionomer interfaces

Model surfacesR Liu et al. Potential-Dependent Infrared Absorption Spectroscopy of Adsorbed CO andX-ray Photoelectron Spectroscopy of Arc-Melted Single-Phase Pt, PtRu, PtOs, PtRuOs,and Ru Electrodes, J. Phys. Chem. B, 104 (15), 3518–3531 (2000)V Stamenkovic et al. Vibrational Properties of CO at the Pt(111)−Solution Interface: theAnomalous Stark-Tuning Slope, JPC B, 109, 678-680 (2005)

MEA Catalyst ionomer interfacesI Kendrick et al. Elucidating the Ionomer-Electrified Metal Interface, J. Am. Chem. Soc.,132 (49), 17611–17616 (2010)S E Evarts et al. Ensemble Site Requirements for Oxidative Adsorption of Methanol andEthanol on Pt Membrane Electrode Assemblies, ACS Catalysis, 2, 701 (2012)I Kendrick et al. Operando Infrared Spectroscopy of the Fuel Cell Membrane Electrode Assembly Nafion-Platinum Interface, International Journal of Hydrogen Energy, 39, 6, 2751-2755 (2014)

8

Potential (mV) Potential (mV) Potential (mV)

Wav

enum

ber (

cm-1

)

30o C 50o C 70o C

9

COads Stark tuning on Pt/Nafion interfaces


Wav

enum

ber (

cm-1

)

30o C 50o C 70o C

Operando Stark tuning at MEA Pt-COads /Nafion interfaces

10


Wav

enum

ber (

cm-1

)

30o C 50o C 70o C

11



Wav

enum

ber (

cm-1

)

30o C 50o C 70o C


12

13

Operando COads Stark tuning elucidates site specific (potential dependent) adsorption sites.

Adsorption potential100 mV




14

1400 1200 1000

1414 cm-1

SO3H νas, COC νas

905 cm-1

SO3H νs, COC νs

1057 cm-1

COC νas, SO3-1 νs

970 cm-1

SO3-1 νs, COC νas,

1400 1300 1200 1100 1000 900

CF2

CF2CF

CF2CF2

OCF2

CF2

(BB) (BB)

(4)

(3)(2)

(1)

CF2

CF2S

O

O

O

M NX

Short Side Chain

3M

Nafion

CF2

CF2CF

CF2CF2

OCF2

F2C

(BB) (BB)

(2)

(1)

S

O

O

O

M NX

Nafion

CF2

CF2CF

CF2CF2

OCF2

CFOF3C

(BB) (BB)

(B) (4)

(3) (2)(1)

(A)

CF2CF2

M

SO O

O

M NX

1400 1200 1000

910 cm-1

SO3H νs, COC-A νs

1414 cm-1

SO3H νas, COC-A νas

1061 cm-1

COC-A νas, SO3-1 νs

970 cm-1

SO3-1 νs, COC-A νas

1400 1300 1200 1100 1000 900

1400 1200 1000

1060 cm-1

SO3-1 νs, COC vs

1412 cm-1

SO3H νas926 cm-1

SO3H νs, COC νs

991 cm-1

SO3-1 νs, COC vas

1400 1300 1200 1100 1000 900

Wavenumber (cm-1)

Hydration dependent IR spectra: Short chain, Nafion & 3M membranes

C3v local symmetry C1 local symmetry

983* (969) cm-1 : SO3- vs, COC-A vas

1059* (1061) cm-1 : COC-A vas, SO3- vs

786* (910) cm-1 : SO3H vs, COC-A vs

1405* (1414) cm-1 : SO3H vas, COC-A vas

Kendrick, I.; Yakaboski, A.; Kingston, E.; Doan, J.; Dimakis, N.; Smotkin, E. S. J. Polym. Sci. Pt. B-Polym. Phys. 2013, 51, 1329.

C3v,LF

C3v,HF C1,HF

C1,LF

15

Nafion exchange-site normal mode animations

Kendrick, I., et al., Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells. Journal of The Electrochemical Society, 2016. 163(4): p. H3152-H3159.

16

Normal mode animation snapshots (C3V): Dissociated exchange sites.

Kendrick, I., et al., Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells. Journal of The Electrochemical Society, 2016. 163(4): p. H3152-H3159.

17

Normal mode animation snapshots (C1): Associated exchange sites.

Freq

uenc

y λavg = 3

λlocal

λavg = 10 λavg = 15

1400 1200 1000 8001400 1200 1000 800 1400 1200 1000 800

Dehydrated Hydrated

Wavenumber (cm-1)

1414 cm-1

SO3H νas, COC-A νas

1061 cm-1

COC-A νas, SO3-1 νs

970 cm-1

SO3-1 νs, COC-A νas

910 cm-1

SO3H νs, COC-A νs

EW ∼ 1100 g32 oligomers 10 side chains separated by 14 -CF2- monomers320 exchange sites

18

RamanInfrared

Wavenumber (cm-1)

1066 cm-1969 cm-1

C1 band 910 cm-1

C3V bands

1200 1000 800

1100 mV

1000 mV

900 mV

800 mV

700 mV600 mV

500 mV

400 mV

300 mV

200 mV

100 mV

0 mV

1200 1100 1000 900 800

Operando spectroscopy: Transitioning between hydration (C3V) and dehydration (C1).

19

C3VC1

Nafion dehydration: C1 modes negatively correlated to C3V modes.

DFT build-up of the exchange site solvation sphere.Transitioning from C1 to C3V local symmetry

Webber et al. Mechanically Coupled Internal Coordinates of Ionomer Vibrational Modes, Macromolecules, 43, 5500-5502 (2010)Kendrick et al. Theoretical and experimental infrared spectra of hydrated and dehydrated Nafion Journal of Polymer Science Part B: Polymer Physics, 51, 18, pp. 1329–1334 (2013)

C1

C3V

• An initial cubic MD box was constructed with side lengths of ∼80 Å (shrank to 75 Å, during preliminary relaxation process)

• (Nafion with ∼20 wt % (H2O, H3O+)• Nafion EWs close to 1100 g/mol

• 32 independent oligomers 10 side chains separated by 14 -CF2- monomers

• 4800 H2O molecules• 320 H3O+ ions

• MD contained total 37,504 atoms. • Effective level of hydration λ= 15.

Karo, J., et al., Molecular Dynamics Modeling of Proton Transport in Nation and HyltonNanostructures. Journal of Physical Chemistry B, 2010. 114(18): p. 6056-6064.

21

Nafion Molecular Dynamics

22

320 S centered10 Å cubes

λlocal =15

λlocal =4

λlocal =0

λavg =15

λlocal =40

λlocal =10

Nafion molecular dynamics: At any λave a λ distribution exists.

Nafion hydration (C3V)/dehydration (C1) of the exchange site environment

• The C1 and C3V group modes involve the same side-chain functional groups (Triflate/COC group modes (C3V) or triflic acid/COC group modes (C1)).

• The C1 and C3V modes do not coexist at extreme states of hydration.

• C1 and C3V modes do coexist at intermediate state-of-hydration and there is a distribution of per site λvalues.

23

Local symmetry

Group Mode Assignment DFT (cm-1) Transmission (cm-1)

HydratedDOW-[H]

C3v,LF SO3-1 νs, COC νas, 923* 970

C3v,HF COC νas, SO3-1 νs 1051* 1057

DehydratedDOW-[H]

C1,LF SO3H νs, COC νs 777* 905C1,MF COC νs , SO3H νas 960* 1001C1,HF SO3H νas, COC νas 1396* 1414

HydratedNafion-[H]

C3ν,LF SO3-1 νs, COC-A νas 983* 969

COC-B νas, CF3 δu, SO3-νs

973* 983

C3v,HF COC-A νas, SO3-1 νs 1059* 1061

DehydratedNafion-[H]

C1,LF SO3H νs, COC-A νs 786* 910CF3 δu, COC-B vas 981* 983

C1,MF CF3 δu, COC-B δs, COC-A ρr, SO3H νas 986* 999sC1,HF SO3H νas, COC-A νas 1405* 1414

Hydrated 3M-[H]

C3v,LF SO3-1 νs, COC vas 975* 991

SO3-1 νs, SC CC v, COC δs 980* 1012

C3v,HF SO3-1 νs, COC vs 1014* 1060

Dehydrated3M-[H]

C1,LF SO3H νs, COC νs 791* 926COC vas 984* 1012

C1,MF COC δs, SO3H νas 1009* 1031C1,HF SO3H νas 1395* 1412

Symmetric stretching, νs; Asymmetric stretching, νas; Wagging, ω; Bending, δs; Umbrella bending, δu; Rocking, ρr;Backbone, BB; Side Chain, SC; Calculated value *

24

IR band assignments of short chain, 3M and Nafion in terms of exchange site local symmetry (manuscript in preparation).

25

Ionomer vibrational band assignments in terms of exchange site local symmetry, and as group modes, are essential for the interpreting operando Raman spectroscopy of the fuel cell catalytic layer.

Operando Raman Spectroscopy of the fuel cell ionomer/Pt interface of a non-PGM catalysts: A case study.

26

Operando confocal Raman micro-spectroscopy depth profiling to select focal point for fuel cell study.

Kendrick et al. Operando Raman Micro-Spectroscopy of Polymer Electrolyte Fuel Cells Journal of The Electrochemical Society, 163 (4) H3152-H3159 (2016)Loupe et al., Twenty years of operando IR, X-ray absorption, and Raman spectroscopy: Direct methanol and hydrogen fuel cells, Catalysis Today, In press, doi:10.1016/j.cattod.2016.06.012

Fuel cell polarization curve

27

C1

C3V

C1+C3V

Fe-Nx/C cathode catalyst operating under O2

C (no Fe) cathode catalyst operating under O2

Fe-Nx/C cathode catalyst operating under N2

631 cm-1

600 cm-1

564 cm-1

631 cm-1

600 cm-1

564 cm-1 631 cm-1

600 cm-1

564 cm-1

0 mV

100 mV

200 mV

300 mV

400 mV

500 mV

600 mV700 mV

800 mV

900 mV

1000 mV

1100 mV

Average

Kendrick Raman cell. Potential-dependent Raman spectra (650 to 550 cm-1) of the Fe-Nx/C cathode catalyst operating under O2 (left), under N2 (middle), and under O2 after Fe removal (right). Absence of Stark tuning of the Fe-O peak at 564 cm-1 confirms Fe-O is not an electrocatalytic site. Analysis of as-received catalyst showed 13.5 ppm Pt.

Operando Raman Micro-Spectroscopy of PEM fuel cell.

Conclusions

• This is the first demonstration of operando Raman spectroscopy of a fuel cell with flowing reactant streams over a standard MEA structure and controlled temperature.

• Stark tuning of the Fe-O site in a non-PGM catalyst was not observed in the operando Raman (i.e., Fe-O peaks were invariant with potential). Catalysis was likely due to Pt contaminant assessed at 13.5 ppm.

• Local symmetry based assignments of short chain, 3M and Nafion vibrational group modes (C1 vs. C3V) enables elucidation of shift of the λ per site distribution with state of hydration. This explains the gradual shift of ionomer spectra from C1 to (C1 + C3V) to C3V characteristics representing fully dehydrated, partially hydrated and totally hydrated exchange site environments respectively.

28

Thanks

Thanks to funding from:NuVant Systems Inc.US Department of Energy EERE (DE-EE-0000459)Army Research Office (W911NF-12-1-0346)

Neili Loupe (NEU): Vibrational band assignments, and IR spectroscopyJonathan Doan (NEU): Vibrational band assignments and IR spectroscopyRyan Cruse (NEU): Per site λ analysisMatthew Ingargiola (NEU): Per site λ analysis Nicholas Dimakis (UT-RGV) : DFT Normal mode analysisKhaldoon Abu-Hakmeh (Georgia Tech): MD simulations of λ = 3, 10 and 15Seung Soon Jang (Georgia Tech): MD simulations of λ = 3, 10 and 15Max Diem (NEU): Raman spectroscopyIan Kendrick (NEU): IR and Raman spectroscopyWilliam A. Goddard III (Cal Tech): MD simulations and use of his X3LYP functional for DFT build-up of hydration sphere.

29

Supplemental slides

The following slides are supplemental slides that were not shown at the CWG.

30

C3v local symmetry C1 local symmetry

1051* (1057) cm-1 : COC vas, SO3- vs

777* (905) cm-1 : SO3H vs, COC vs

C3v,LF

C3v,HF C1,HF

C1,LF

31

Short Side-Chain exchange-site normal modes

923* (970) cm-1 : SO3- vs, COC vas

1396* (1414) cm-1 : SO3H vas, COC vas

C3v local symmetry

975* (991) cm-1 : SO3- vs, COC vas

1014* (1060) cm-1 : SO3-1 νs, COC vs 1395* (1412) cm-1 : SO3H vas

C3v,LF

C3v,HF C1,HF

C1,LF

32

3M PFSA exchange-site normal modesC1 local symmetry

791* (926) cm-1 : SO3H vs, COC vs

The metal-oxygen bond dissociation energy (Do 298 K (M-O)) in diatomic molecules versus group. Periods are determined by symbols.

Face centered cubic (FCC) phase compositions in the PtRuOs system.

Ley diagram

33

C3v,HFC1,HF C1,LF C3v,LF

State-of-hydration dependent IR spectra

34

CF2

CF2CF

CF2CF2

OCF2

CF2

(BB) (BB)

(4)

(3)(2)

(1)

CF2

CF2S

O

O

O

M NX

Short Side Chain

3M

Nafion

CF2

CF2CF

CF2CF2

OCF2

F2C

(BB) (BB)

(2)

(1)

S

O

O

O

M NX

Nafion

CF2

CF2CF

CF2CF2

OCF2

CFOF3C

(BB) (BB)

(B) (4)

(3) (2)(1)

(A)

CF2CF2

M

SO O

O

M NX

operando ir and raman spectroscopy of the catalyst ionomer

Documents