Ruthenium based non platinum catalysts for oxygen reduction

in acid solution

Alex SchechterAriel University Center

ISRAEL למקורות אנרגיה מתקדמים7הכנס ה-

26 January 2011אוניברסיטת ת"א

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Fuel cell

Methanol fueled Electric vehiclee-e-

DMFC Concept

Membrane/ Separator/ Electrolyte

6e- 6e-

In Air – O2

Water + Methanol Residue

3H2O

CO2 Out

Methanol solution In

6H+

Anode Cathode

Pt Short Comings in PEMFC and DMFC

1. Slow oxygen reduction kinetics is the main contributor to efficiency loses (70%) in H2/Air PEMFC

2. Pt is Pt alloys show the best performance but very high cost (USD/oz 1651 Oct. 2010), estimated 0.8g/kW mostly in the cathode

1. In DMFC ,Pt poisoning by methanol (“crossover”) further decrease ORR rate, increase the over potential and cathode loading by a factor of~ 10

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Promissing Non-Pt catalyst

• Oxide based catalyst• Macro cycles (M=Co ,Fe, Mn)

• Chevrel phaseRuthenium chevrel phases with Se, S, Te and N

Wolf Vielstich: Handbook of Fuel Cells

Alonso-Vante N, Bogdanoff P, Tributsch H (2000) J Catal190:240

e-e-

Cluster charge transfer Ru2Mo6Se8

W. Jaegermann, C. Pettenkoffer, N. Alonso-Vante, Th. Schwazlose and H. Tributsch, Ber. Bunsenges. Phys. Chem., 94,513 (1990)

e-e-

Precursors- •Ru3CO12, RuCl3

•Elemental S/Se/Te powder

Methods- •Reflux 12-48hours in Xylene or ethylene glycol•Thermolysis 1200-1700ºC

Conventional Synthesis methods of RuxLy (L=S,Se,Te) e-e-

RuSe catalyst Mechanisms

• Carbonyl – cluster theory

• The surfaces of Ru particles are occupied by small Ru selenide clusters

M. Bron: J of Electroanalytical Chem 500:510Tributsch H, Bron M, Hilgendorff M, Schulenburg H, Dorbandt I,Eyert V, Bogdanoff P, Fiechter S (2001) J Appl Electrochem ,31:739

1. Find an effective method of preparing RuxSey

2. Characterize these materials

3. Study oxygen reduction reaction (ORR) on RuxSey in aspects related to fuel cells

Objectives

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e-e-

Microwave Synthesis of Nano-Catalysts

C2H4(OH)2 C2H4(OH)O· + H·H· H+ + e-

Ru3+ +3e- Ru Eo= 0.703VH2SeO3 + 4H+ + 4e- Se + 3H2O Eo= 0.74V

Electron Microscopy of RuxSey

HRSEM TEM

RuCl3 : elemental Se powder 2:1 (molar)

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Carbon

Nano-catalyst

Se-L Ru-L

pt1 93.94 6.06

pt2 20.36 79.64

pt3 14.23 85.77

pt4 92.90 7.10

Se-L Ru-L

pt1 32.23 66.77

pt2 35.12 64.88

pt3 35.19 64.81

Ru and Se values are given in atomic percent

Ru2Se from Se powder Ru2Se from H2SeO3

EDX Mapping e-e-

Simultaneous DSC /TGA analysis (Ru2Se)

Se powder

H2SeO3

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e-e- Quantitative Analysis of Se Powder in RuxSey

3.3% elemental Se

Melting Se

221 80m f

JT C H

gr

In Ru:Se 2:1 (33%Se) Ru2Se17.3 (EDX) + 3.3%Se (STA) + 12.4%Se washed

Inte

nsity

(a.u

)2θ2θ

Inte

nsity

(a.u

)

Se 100

Se 101

Se 110Se 200

Se 201Se 112 Se 210

Ru 100

Ru 002

Ru 101, Se 102

Ru 112 Ru 110

Ru 103

RuSe2 111

RuSe2 210 RuSe2 311

RuSe2 321

Ru2Se

RuSe2

Ru10Se

Elemental Se powder H2SeO3

XRD patterns of RuxSey nano-catalysts e-e-

Inte

nsit

y (a

.uθ

RuSe2 321

RuSe2 311

RuSe2 111

RuSe2 210

Ru10Se

Ru2Se

RuSe2

Rotating Ring Disc Electrode (RRDE)

The Koutecky-Levich equation: 21

11111

Biiii kkd

oL CnFDi 21613262.0 The Levich equation:

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e-e-

RuxSey

N2

O2 0 rpm

O2 300 rpm

O2 600 rpm

O2 900 rpmO2 1200 rpm

O2 1800 rpm

O2 2400 rpmO2 3000 rpm

MoxRuySez Curr

ent A

mp

cm-2

x10

-4

Curr

ent A

mp

cm-2

x10

-4

LSV of O2 reduction on RDE

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

Cu

rren

t I R

[A

]

-1.20E-03

-1.00E-03

-8.00E-04

-6.00E-04

-4.00E-04

-2.00E-04

0.00E+00

2.00E-04

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Potential [V vs. NHE]

Cu

rre

nt

I D [A

]

2400 rpm

1800 rpm

1200 rpm

600 rpm

300 rpm

200 rpm

100 rpm

50 rpm

RRDE result of Ru80Se20

Ring

DiscCur

rent

A/c

m2

e-e-

-6

-5.5

-5

-4.5

-4

-3.5

-3

-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05

log

, A

overpotential, V-7

-6.5

-6

-5.5

-5

-4.5

-4

-3.5

-3

-2.5

-0.25 -0.2 -0.15 -0.1 -0.05 0

log

ik, A

overpotential, V

b=61 mV/decade

b=112 mV/decade

b=87 mV/decade

b=91 mV/decade

RuxSey Pt

RDE electrodes in 0.5M H2SO4 solution. Scan rate=2 mV/sec, ω=1800 rpm.

e-e-Tafel plots of O2 reduction on Ru2Se and Pt

ik and B (@E=200 mV) values calculated from the Koutecky-Levich plots

Nano catalyst

ik (A/cm2)B (A/rpm-1/2)

RuxSey0.02780.000149

RuxSy0.01330.000314

RuxTey0.00910.000164

MoxRuySez0.00220.000094

MoxRuySz0.00360.000124

MoxRuyTez0.01180.000156

e-e-

RuxSey

Pt

RuxSey

Pt

(a) (b)RuxSey

Pt

RuxSey

Pt

(a) (b)

e-e-

Hydrogen Peroxide Oxidation on RRDE Pt ring

Potential [V vs. Ag/AgCl]

Cu

rren

t m

icro

Am

p/c

m2

Disk

Disk

η = 50-125 mV η = 125-200 mV

Tafel slopes vs. Se molar percent (EDX) in RuxSey (H2SeO3)e-e-

η = 50-125 mV η = 125-200 mV

Exchange current density vs. Se molar percent in RuxSey (H2SeO3)

e-e-

Se content affect the number of active sites and not in the activation energy

NII rd 1

21

)1(1

N

kx

N

x

I

I

r

d

Only (2)&(3): x=0 2121 NkNII rd

Only (1)&(2): k3=0 NxII rd )1( All reactions

e-e- dmeOx k Re1 1

IntenmOx k 2)(2

dneInt k Re3 3

x(k1,k2)

A. Damjanovic, M. A. Genshaw, and J. O’M. Bockris, J. Chem. Phys., 45, 4057 (1966)

ORR Mechanism

Rough Surfaces in RRDE-ORR Mechanism Study e-e-

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

250 300 350 400 450 500 550 600 650

rate

co

nst

ant

E, mV vs Ag/AgCl

k1 k2 k3

e-e-

Kinetic constants of ORR on Ru2SeRa

te c

onst

ants

mol

e/se

c

k1

k2

k3

Methanol Oxidation

Oxygen Reduction

oxygen reduction on Ru2Se versus Pt in the Presence of methanol @0.4 V

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Ru2Se/C Electrode in 1M MeOH/5M H3PO4 at 60°C

1st day

4th day

7th day

Curr

ent A

mp/

cm2

e-e-

Stability of ORR Activity of Ru2Se Catalyste-e-

Measured at 0.3 V ,during storage in 5M H3PO4 solution @ 60C

Pt

Ru 2Se (powder Se)Ru2 Se (H2SeO3(

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Fuel cell Testing in DMFC: Pt versus RuxSey

•Conditions: T= 25oC, 1M CH3OH, air 150 ml/min

0123456789

10

0 0.05 0.1 0.15 0.2 0.25 0.3

P, m

W/c

m2

I, A

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.05 0.1 0.15 0.2 0.25 0.3

E, V

I, A

Pt

RuxSey

RuxSey

Pt

020406080

100120140160180200

0 0.05 0.1 0.15 0.2 0.25 0.3

P, m

W/g

cat

alys

t

I, A

RuxSey

Pt

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Power Per Gram of Cathode Catalyst

State of the art comparison

Summary RuxSey synthesis can be controlled by microwave

Optimum ORR kinetics is seen in Ru2Se (~35% Se)

Mostly 4e- oxygen reaction occur, distinctly at high over potential

Unlike previous reports – RuSe presents high stability and excellent methanol tolerance

Further inmprovment of catalytic performance is required to compete with Pt.

Acknowledgments

Dr. Hanan Teller

Dr. Oleg Stanevsky

Dr. Maria Rylov

Mr. Phillip Hoffhimer

Mr. Avinoam Burnstien

Mrs. Mietal Gor

Mr. Victor Moltenan

Mr. Rami Kriger

Funding: Israeli Ministry of National Infrastructures

Thank You

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