Transcript RuSe ORR catalyst

Ruthenium based non platinum
catalysts for oxygen reduction in
acid solution
Alex Schechter
Ariel University Center
ISRAEL
‫ למקורות אנרגיה מתקדמים‬7-‫הכנס ה‬
26 January 2011
‫אוניברסיטת ת"א‬
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Methanol fueled Electric vehicle
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Fuel
cell
DMFC Concept
Anode
6e-
6e-
Methanol
solution In
Cathode
In Air
– O2
Membrane/
Separator/
Electrolyte
CO2 Out
Water +
Methanol
Residue
6H+
3H2O
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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 phase
Ruthenium 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
Cluster charge transfer Ru2Mo6Se8
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W. Jaegermann, C. Pettenkoffer, N. Alonso-Vante, Th. Schwazlose and H. Tributsch, Ber. Bunsenges. Phys. Chem.,
94,513 (1990)
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Conventional Synthesis methods of RuxLy
(L=S,Se,Te)
Precursors•Ru3CO12, RuCl3
•Elemental S/Se/Te powder
Methods•Reflux 12-48hours in Xylene or ethylene
glycol
•Thermolysis 1200-1700ºC
RuSe catalyst Mechanisms
• Carbonyl – cluster
theory
• The surfaces of Ru
particles are occupied
by small Ru selenide
clusters
M. Bron: J of Electroanalytical Chem 500:510
Tributsch H, Bron M, Hilgendorff M, Schulenburg H, Dorbandt I,Eyert V, Bogdanoff P, Fiechter S (2001) J Appl Electrochem ,31:739
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Objectives
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
Microwave Synthesis of Nano-Catalysts
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C2H4(OH)2  C2H4(OH)O· + H·
H·  H+ + eRu3+ +3e-  Ru Eo= 0.703V
H2SeO3 + 4H+ + 4e-  Se + 3H2O Eo= 0.74V
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Electron Microscopy of RuxSey
HRSEM
TEM
Carbon
Nano-catalyst
RuCl3 : elemental Se powder 2:1 (molar)
EDX Mapping
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Ru2Se from Se powder
Se-L
Ru-L
pt1
93.94
6.06
pt2
20.36
79.64
pt3
14.23
85.77
pt4
92.90
7.10
Ru2Se from H2SeO3
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
Simultaneous DSC /TGA analysis (Ru2Se)
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H2SeO3
Se powder
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Quantitative Analysis of Se Powder in RuxSey
Tm  221C
H f  80
J
gr
Melting Se
3.3% elemental Se
In Ru:Se 2:1 (33%Se)  Ru2Se17.3 (EDX) + 3.3%Se (STA) + 12.4%Se washed
XRD patterns of RuxSey nano-catalysts
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Elemental Se powder
H2SeO3
RuSe2 210
RuSe2 321
Ru2Se
Ru 101, Se 102
Se 100
Ru 002
Se 110
Ru 100
Se 200
Se 201
Se 112
2θ
RuSe2
Ru 112
Ru 110
Se 210
RuSe2 111
(a.u
Intensity(a.u)
Intensity
Intensity (a.u)
Ru10Se
Se 101
RuSe2 311
Ru10Se
Ru2Se
RuSe2 210
RuSe2 311
RuSe2 111
RuSe2 321
Ru 103
2θ θ
RuSe2
Rotating Ring Disc Electrode (RRDE)
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The Levich equation:
The Koutecky-Levich equation:
iL  0.62nFD2 3 1 61 2Co
1 1 1 1
1
   
i id ik ik B1 2
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Current Amp cm-2 x10-4
MoxRuySez
Current Amp cm-2 x10-4
LSV of O2 reduction on RDE
N2
O2 0 rpm
O2 300 rpm
O2 600 rpm
O2 900 rpm
O2 1200 rpm
O2 1800 rpm
O2 2400 rpm
O2 3000 rpm
RuxSey
RRDE result of Ru80Se20
2.50E-06
2.00E-06
Current A/cm2
Current I R [A]
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Ring
1.50E-06
1.00E-06
5.00E-07
2.00E-04
0.00E+00
0.00E+00
Current ID [A]
-2.00E-04
Disc
-4.00E-04
2400 rpm
1800 rpm
1200 rpm
600 rpm
-6.00E-04
300 rpm
200 rpm
100 rpm
50 rpm
-8.00E-04
-1.00E-03
-1.20E-03
0
0.1
0.2
0.3
0.4
0.5
0.6
Potential [V vs. NHE]
0.7
0.8
0.9
1
Tafel plots of O2 reduction on Ru2Se and Pt
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-3
-0.25
-0.2
-0.15
-0.1
-0.05
0
-2.5
-0.25
-3
0.05
-0.2
-0.15
-0.1
-0.05
-3.5
b=112 mV/decade
RuxSey
-4.5
b=87 mV/decade
b=91 mV/decade
-4
log ik, A
log , A
-4
-5
-3.5
-4.5
Pt
-5
-5.5
b=61 mV/decade
-6
-5.5
-6.5
-7
-6
overpotential, V
RDE electrodes in 0.5M H2SO4 solution. Scan rate=2 mV/sec, ω=1800 rpm.
overpotential, V
0
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ik and B (@E=200 mV) values calculated
from the Koutecky-Levich plots
Nano
catalyst
RuxSey
RuxSy
RuxTey
MoxRuySez
MoxRuySz
MoxRuyTez
ik (A/cm2)
B (A/rpm-1/2)
0.0278
0.0133
0.0091
0.0022
0.0036
0.0118
0.000149
0.000314
0.000164
0.000094
0.000124
0.000156
Hydrogen Peroxide Oxidation on RRDE Pt ring
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1.4
1.2
RuxSeyDisk
% ir/id
Current microAmp/cm2
(a)
PtDisk
1
0.8
0.6
0.4
0.8
Potential [V vs. Ag/AgCl]
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Tafel slopes vs. Se molar percent (EDX) in RuxSey (H2SeO3)
η = 50-125 mV
η = 125-200 mV
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Exchange current density vs. Se molar percent
in RuxSey (H2SeO3)
η = 50-125 mV
η = 125-200 mV
Se content affect the number of active sites and not in
the activation energy
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1
ORR Mechanism
2 
3

Ox  m e 
 Re d
k2
Ox  ( m  n )e  
Int
I d x  1 ( x  1)k 


Ir
N
N1 2
x(k1,k2)
k3
Int  ne 

Re d
Only (2): k1=0, k30  I d I r  1 N
Only (1)&(2): k3=0
k1
Only (2)&(3): x=0  I d I r  1 N  2k  N1 2
I d I r  ( x  1) N
All reactions
A. Damjanovic, M. A. Genshaw, and J. O’M. Bockris, J. Chem. Phys., 45, 4057 (1966)
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Rough Surfaces in RRDE-ORR Mechanism Study
Kinetic constants of ORR on Ru2Se
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0.004
k1
rate constant
mole/sec
Rate constants
0.0035
0.003
0.0025
k3
0.002
0.0015
0.001
k2
0.0005
0
250
300
350
400
450
E, mV vs Ag/AgCl
k1
k2
k3
500
550
600
650
oxygen reduction on Ru2Se versus Pt in the
Presence of methanol @0.4 V
1
Pt/C
0.8
Disk Current, mA/cm2
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Ru2Se/C
Oxygen Reduction
0.6
0.4
0.2
0
-0.2
Methanol Oxidation
-0.4
0
0.5
1
1.5
2
2.5
Methanol Concentration, mol/l
3
3.5
4
Ru2Se/C Electrode in 1M MeOH/5M H3PO4 at 60°C
Current Amp/cm2
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1st day
4th day
7th day
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Stability of ORR Activity of Ru2Se Catalyst
Pt
Ru 2Se (powder Se)
Ru2Se (H 2SeO 3)
Measured at 0.3 V ,during storage in 5M H3PO4 solution @ 60C
P, mW/cm2
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Fuel cell Testing in
DMFC: Pt versus RuxSey
10
9
8
7
6
5
4
3
2
1
0
Pt
RuxSey
0
0.05
0.1
0.15
I, A
0.2
0.25
0.7
0.6
E, V
0.5
0.4
Pt
0.3
0.2
RuxSey
0.1
0
0
0.05
0.1
0.15
I, A
0.2
0.25
0.3
•Conditions: T= 25oC, 1M
CH3OH, air 150 ml/min
0.3
State of the art comparison
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P, mW/g catalyst
Power Per Gram of Cathode Catalyst
200
180
160
140
120
100
80
60
40
20
0
Pt
RuxSey
0
0.05
0.1
0.15
I, A
0.2
0.25
0.3
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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