1. Ariel University Center
Ruthenium based non platinum catalysts for oxygen reduction in acid solution
Alex Schechter
Ariel University Center
ISRAEL
הכנס ה-7 למקורות אנרגיה מתקדמים
26 January 2011
אוניברסיטת ת"א

2. Methanol fueled Electric vehicle
Fuel cell

3. Membrane/ Separator/ Electrolyte
DMFC Concept
Membrane/ Separator/ Electrolyte
6e-
In Air – O2
Water + Methanol Residue
3H2O
CO2 Out
Methanol solution In
6H+
Anode
Cathode

4. Pt Short Comings in PEMFC and DMFC
Slow oxygen reduction kinetics is the main contributor to efficiency loses (70%) in H2/Air PEMFC
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
In DMFC ,Pt poisoning by methanol (“crossover”) further decrease ORR rate, increase the over potential and cathode loading by a factor of~ 10

5. Promissing Non-Pt catalyst
Oxide based catalyst
Macro cycles (M=Co ,Fe, Mn)
Chevrel phase
Ruthenium chevrel phases
with Se, S, Te and N
Oxide based mainly for SOFC
Macro cycles: The structure can be compared to the one of the functional group of chlorophyll or hemoglobin. Newer days they were heat treated to improve the stability and the ORR activity. Than embedded metallic catalytically active centers are formed
Chevrel phases:
Generally referred as “ternary molybdenum chalcogenides” but named after the scientist Chevrel
General structure MxMo6X8 (M = Fe, Cu, Ag…, X = Se, S, Te)
Electro catalytic properties first discovered by Alonso-Vante & Tributsch in 1986 → Show good performance and selectivity!
→ Based on these Chevrel phases the nanostructured RuSe cluster catalyst which we deal with developed → Mainly RuxSey/C catalyst but also RuxSzSey/C
→ There from now on the presentation is only about Ru-catalyst
Wolf Vielstich: Handbook of Fuel Cells
Alonso-Vante N, Bogdanoff P, Tributsch H (2000) J Catal190:240

6. Cluster charge transfer Ru2Mo6Se8
W. Jaegermann, C. Pettenkoffer, N. Alonso-Vante, Th. Schwazlose and H. Tributsch, Ber. Bunsenges. Phys. Chem., 94,513 (1990)

7. 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 ºC

8. RuSe catalyst Mechanisms
Carbonyl – cluster theory
The surfaces of Ru particles are occupied by small Ru selenide clusters
Theory: Selenium acts as a electron bridge and a changing Tafel slope also indicates a modification in structure.
Theory: For low Se contents (<40%) → at higher concentrations hexagonal Ru cores are covered by laminar structures of Ru selenide shells
→ but generally the processes are not understood in detail so far
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

9. Objectives Find an effective method of preparing RuxSey
Characterize these materials
Study oxygen reduction reaction (ORR) on RuxSey in aspects related to fuel cells

10. Microwave Synthesis of Nano-Catalysts
C2H4(OH)2  C2H4(OH)O· + H·
H·  H+ + e-
Ru3+ +3e-  Ru Eo= 0.703V
H2SeO3 + 4H+ + 4e-  Se + 3H2O Eo= 0.74V

11. Electron Microscopy of RuxSey
HRSEM
TEM
RuCl3 : elemental Se powder 2:1 (molar)

12. Ru and Se values are given in atomic percent
EDX Mapping
Ru2Se from Se powder
Ru2Se from H2SeO3
Ru and Se values are given in atomic percent

13. Simultaneous DSC /TGA analysis (Ru2Se)
H2SeO3
Se powder

14. In Ru:Se 2:1 (33%Se)  Ru2Se17.3 (EDX) + 3.3%Se (STA) + 12.4%Se washed
Quantitative Analysis of Se Powder in RuxSey
Melting Se
3.3% elemental Se
In Ru:Se 2:1 (33%Se)  Ru2Se17.3 (EDX) + 3.3%Se (STA) %Se washed

15. XRD patterns of RuxSey nano-catalysts
Elemental Se powder
H2SeO3
RuSe2 321
RuSe2 311
RuSe2 111
RuSe2 210
Ru10Se
Ru10Se
Ru2Se
Ru2Se
RuSe2
RuSe2

16. Rotating Ring Disc Electrode (RRDE)
The Levich equation:
The Koutecky-Levich equation:

17. LSV of O2 reduction on RDE
RuxSey N2
O2 0 rpm
O2 300 rpm
O2 600 rpm
O2 900 rpm
O rpm
O rpm
O rpm
O rpm
Current Amp cm-2 x10-4
MoxRuySez
Current Amp cm-2 x10-4

18. RRDE result of Ru80Se20
Ring
Current A/cm2
Disc

19. Tafel plots of O2 reduction on Ru2Se and Pt
RDE electrodes in 0.5M H2SO4 solution. Scan rate=2 mV/sec, ω=1800 rpm.

20. ik and B (@E=200 mV) values calculated from the Koutecky-Levich plots
Nano catalyst
ik (A/cm2)
B (A/rpm-1/2)
RuxSey
0.0278
RuxSy
0.0133
RuxTey
0.0091
MoxRuySez
0.0022
MoxRuySz
0.0036
MoxRuyTez
0.0118

21. Hydrogen Peroxide Oxidation on RRDE Pt ring
Disk
Current microAmp/cm2
Disk
Potential [V vs. Ag/AgCl]

22. Tafel slopes vs. Se molar percent (EDX) in RuxSey (H2SeO3)
η = mV
η = mV

23. Exchange current density vs. Se molar percent in RuxSey (H2SeO3)
η = mV
η = mV
Se content affect the number of active sites and not in the activation energy

24. ORR Mechanism x(k1,k2) Only (2)&(3): x=0  Only (2): k1=0, k30 
All reactions
A. Damjanovic, M. A. Genshaw, and J. O’M. Bockris, J. Chem. Phys., 45, 4057 (1966)

25. Rough Surfaces in RRDE-ORR Mechanism Study

26. Kinetic constants of ORR on Ru2Se
Rate constants mole/sec k2

27. oxygen reduction on Ru2Se versus Pt in the Presence of methanol @0.4 V
Methanol Oxidation

28. Ru2Se/C Electrode in 1M MeOH/5M H3PO4 at 60°C
1st day
Current Amp/cm2
4th day
7th day

29. Stability of ORR Activity of Ru2Se CatalystPt Ru 2
Se (powder Se)
Se (H
SeO 3 )
Measured at 0.3 V ,during storage in 5M H3PO4 60C

30. Fuel cell Testing in DMFC: Pt versus RuxSey
Conditions: T= 25oC, 1M CH3OH, air 150 ml/min

31. State of the art comparison
Power Per Gram of Cathode Catalyst Pt
RuxSey

32. 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.

33. 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

34. Thank You