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 e- Methanol fueled Electric vehicle e- Fuel cell DMFC Concept Anode 6e- 6e- Methanol solution In Cathode In Air – O2 Membrane/ Separator/ Electrolyte CO2 Out Water + Methanol Residue 6H+ 3H2O e- 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 e- 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 e- W. Jaegermann, C. Pettenkoffer, N. Alonso-Vante, Th. Schwazlose and H. Tributsch, Ber. Bunsenges. Phys. Chem., 94,513 (1990) e- 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 e- 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 e- C2H4(OH)2 C2H4(OH)O· + H· H· H+ + eRu3+ +3e- Ru Eo= 0.703V H2SeO3 + 4H+ + 4e- Se + 3H2O Eo= 0.74V e- Electron Microscopy of RuxSey HRSEM TEM Carbon Nano-catalyst RuCl3 : elemental Se powder 2:1 (molar) EDX Mapping e- 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) e- H2SeO3 Se powder e- Quantitative Analysis of Se Powder in RuxSey Tm 221C 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 e- 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) e- The Levich equation: The Koutecky-Levich equation: iL 0.62nFD2 3 1 61 2Co 1 1 1 1 1 i id ik ik B1 2 e- 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] e- 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 e- -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 e- 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 e- 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] e- Tafel slopes vs. Se molar percent (EDX) in RuxSey (H2SeO3) η = 50-125 mV η = 125-200 mV e- 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 e- 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 N1 2 x(k1,k2) k3 Int ne Re d Only (2): k1=0, k30 I d I r 1 N Only (1)&(2): k3=0 k1 Only (2)&(3): x=0 I d I r 1 N 2k N1 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) e- Rough Surfaces in RRDE-ORR Mechanism Study Kinetic constants of ORR on Ru2Se e- 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 e- 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 e- 1st day 4th day 7th day e- 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 e- 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 e- 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 e-