Fuel Cell. Byungwoo Park. Department of Materials Science and Engineering Seoul National University.

Transcription

1 Fuel Cell Byungwoo Park Department of Materials Science and Engineering Seoul National University 1

2 Environment-Friendly Power Sources Laptop Samsung SDI Power Sources for the Next Generation Cellular Phone LG Chem. Fuel Cell Yejun LEV Hyundai Motor PMP Samsung SDI 2

3 Fuel Cell (PEMFC: η = 83% / DMFC: η = 97% at 298 K) Hydrogen (PEMFC) Methanol + Water (DMFC) Load e - e - H + Catalysts Catalysts E cat Oxygen or Air Φ Carbon Dioxide (DMFC) E ano Anode Membrane (Nafion) Cathode Water Heat 2H 2 4H + + 4e - E ano = 0 V (Hydrogen Oxidation) CH 3 OH + H 2 O CO 2 + 6H + + 6e - E ano = 0.05 V (Methanol Oxidation) PEMFC (1.23 V) DMFC (1.18 V) O 2 + 4H + + 4e - 2H 2 O E cat = 1.23 V (Oxygen Reduction) 3/2O 2 + 6H + + 6e - 3H 2 O E cat = 1.23 V (Oxygen Reduction) Goals: - Catalytic Activity Stability Fuel Cell Yejun Nanostructured Materials 3

4 Produced electrical energy ΔG (T 1 ) Maximum efficiency possible = Χ 100% (Thermodynamic efficiency) ΔH (T 1 ) Total enthalpy produced during a chemical reaction ΔG = ΔH - TΔS Thermodynamic Efficiency = 100% at 0 K. Change in Gibbs free energy J. Larminie and A. Dicks Fuel cell systems Explained, p. 25, (2000). Change in Enthalpy H 2 O (g) kj/mol [Δ f H ( K)] kj/mol [H ( K) H (0 K)] H 2 O (l) kj/mol [Δ f H ( K)] kj/mol [H ( K) H (0 K)] Fuel Cell Yejun D. R. Lide, CRC Handbook of Chemistry and Physics, p. 5-2 (2000).

5 Types of Fuel Cells Electrolyte Operating Temperature Charge Carrier Catalyst Power SOFC (Solid Oxide Fuel Cell) Ceramic (YSZ) 1000 C O 2- Perovskites MW MCFC (Molten Carbonate Fuel Cell) PAFC (Phosphoric Acid Fuel Cell) Immobilized Liquid Molten Carbonate Immobilized Liquid Phosphoric Acid 650 C CO 3 2- Ni MW 200 C H + Pt kw PEMFC (Proton Exchange Membrane Fuel Cell) Ion Exchange Membrane (Nafion) 80 C H + or OH - Pt kw-w DMFC (Direct Methanol Fuel Cell) + DAFC Ion Exchange Membrane (Nafion) C H + or OH - Pt, Pt-Ru W (Direct Alcohol Fuel Cell) Fuel Cell Chunjoong 5

6 Fuel-Cell Components ~1960 Anode Cathode Nafion Membrane Hydrophilic Hydrophobic U. Stimming s Group, Technische Universität München Fuel Cells (2001). Fuel Cell Yejun 6

7 Fuel Cell Chunjoong 7

8 State of Understanding for Nafion Polymer Structure CF 2 CF 2 CF CF 2 x O y - Difficult synthetic process hydrophobic CF 2 - Poor conductivity at high temperature - Methanol crossover - High material cost hydrophilic m CF O CF 3 CF 2 SO 3 - H + x=5, y=1000 m=0~3 K. A. Mauritz s group, The University of Southern Mississippi Chem. Rev. (2004). Fuel Cell Chunjoong 8

9 The Role of Electrocatalyst The use of electrocatalysts serves faster kinetic paths. Two ways to get over the energy hill Free Energy Reactants 1) The use of catalysts. 2) Raising the temperature. Products Reaction Progress W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). Fuel Cell Chunjoong 9

10 Electrocatalysts: Supplying Different Paths by Total-Energy Calculation Uncatalyzed Reaction Reactants Products Catalyzed Reaction Reactants Products Intermediate 1 Intermediate 2 Potential Energy Y Coordinate Transition State Reactants Reactants Fuel Cell Chunjoong Products X Coordinate Transition State Products Reaction Coordinate Potential Energy Reactants Intermediate 1 Y Coordinate Products Intermediate 1 Products Reaction Coordinate X Coordinate Reactants Intermediate 2 Reactants Intermediate 2 Products Reaction Coordinate W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). 10

11 Reactions on Pt Catalysts Hydrogen Oxidation Water Oxidation Pt-H Pt + H + + e - Pt-H 2 O Pt-OH + H + + e - Pt-OH Pt-O + H + + e Pt (110) W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). Pt (110) Pt (100) Current Density (μa/cm 2 ) Pt (110) Pt (100) Pt (100) Current Density (μa/cm 2 ) Pt (111) -150 Hydrogen Reduction Pt + H + + e - Pt-H Potential (V) vs. NHE Oxygen Reduction Pt-O + H + + e - Pt-OH Pt-OH + H + + e - Pt-H 2 O Potential (V) vs. NHE Surface Orientation Dependency (Single Crystal) Fuel Cell Chunjoong 11

12 Hydrogen Oxidation Reaction (HOR) vs. Metal-Hydrogen Bonding Energy Exchange current Exchange current is determined by M-H bonding strength. W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). Fuel Cell Chunjoong 12

13 Oxygen-Reduction Reaction (ORR) and Tafel Slope Rotating Disk Electrodes K. E. Swider-Lyons Group, Naval Research Laboratory J. Electrochem. Soc. (2004). Tafel Slope log i = log i o βnf/rtη Tafel slope Double layer Electrode Diffusion layer Bulk solution Convection i: current density i 0 : exchange current density F: Faraday constant n: the number of electrons involved in the reaction β: symmetry constant η: overpotential Fuel Cell Yejun 13

14 Reaction Mechanisms of ORR W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). δ - H + δ - δ - H + Four-Electron Process H + δ - H H δ - H + O 2 δ- First Adsorption 2O δ- Second Adsorption (Oxygen dissociation) 4-electron reduction of oxygen to water O 2 + 4e - + 4H + 2H 2 O E 0 = V vs. NHE δ - O 2 δ- First adsorption H H δ - + Two-Electron Process 2-electron reduction of oxygen to peroxide (H 2 O 2 ) Fuel Cell Chunjoong and Yejun 14

15 Reaction Mechanisms of ORR ORR pathway is more complex than HOR. Mechanisms are not known exactly. W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). Fuel Cell Chunjoong 15

16 Mechanisms of Methanol Oxidation CH 3 OH + H 2 O CO 2 + 6H + + 6e - E = 0.05 V -H -H CH 3 OH CH 2 OH CHOH COH CH 2 O CHO (HCHO) -H CO HCOOH COOH CO 2 -H +OH -H Fuel Cell Yejun 16

17 CO Tolerant Catalyst Bimetallic Function (CH 3 OH) ad (CO) ad + 4H + + 4e - Ru + H 2 O (OH) ad + H + + e- Pt(CO) ad + Ru(OH) ad CO 2 + H + + e - W. Vielstich, A. Lamm, and H. A. Gasteiger Handbook of Fuel Cells, John Wiley & Sons Ltd (2003). Fuel Cell Chunjoong 17

18 PtRu Catalysts for Enhanced CO Oxidation 1. Bifunctional Effect O C H O Ru provides active OH in the low potential (<0.3 V) Pt-CO + Ru-OH Pt + Ru + CO 2 + H + + e - Pt Ru Watanabe s Group, J. Electroanal. Chem. 60, 267 (1975). Cairns s Group, J. Phys. Chem. 97, (1993). 2. Electronic Effect O C Reduction in density of states on the Fermi level Reduce the bonding energy between CO and Pt Pt Ru Rameshand s Group, Chem. Mater. 1, 391 (1989). Wiekowski s Group, J. Phys. Chem. 98, 5074 (1994). e - Fuel Cell Yejun 18

19 High-Efficiency Catalysts for Oxygen Reduction Nanostructure-Tailored Catalysts N. M. Markovic s Group, Argonne National Lab. Nature Mater. (2007). Fuel Cell Chunjoong 19

20 Fuel Cell Yejun 20

21 Comparison of Several Pt 3 M Alloys N. M. Markovic s Group, Argonne National Lab. Nature Mater. (2007). Pt 3 Co Nanoparticle Fuel Cell Yejun 21

22 Vital Role of Moisture in the Catalytic Activity Activation of oxygen by water Masakazu Date s Group, AIST (Japan) Angew. Chem. Int. Ed. (2004). (p): interface, (s): support, (g): gas Fuel Cell Yejun 22

23 CO Oxidation Experiments with O 2 and partial H 2 O Fuel Cell Yejun 23

24 Fuel Cell Yejun 24

25 Tin-Oxide Supported Au Nanoparticle Catalysts SnO x ~ partly amorphous ~ alkaline nature Au ~ 1.7 nm No peroxide 0.2V K. E. Swider-Lyons Group, Naval Research Laboratory J. Electrochem. Soc. (2006). Fuel Cell Yejun 25

26 Modifying Catalytic Reactivity by Surface Dealloying Peter Strasser s Group, University of Houston J. Am. Chem. Soc. (2007). Fuel Cell Yejun 26

27 Fuel Cell Yejun 27

28 Alternative Fuels Fuel Cell Yejun 28

29 Alternative Fuels Mark S. Wrighton's Group, Massachusetts Institute of Technology J. Phys. Chem. B (1998). Requirements - Low to no toxicity - Facility to store and handle safely - High energy density - Oxidation potential close to the H + /H 2 couple Fuel Cell Yejun 29

30 Alternative Fuels Mark S. Wrighton's Group, Massachusetts Institute of Technology J. Phys. Chem. B (1998). Fuel Cell Yejun 30

31 Fuel Cell Yejun 31

32 Pt-Ru vs. Pt-Sn Mark S. Wrighton's Group, Massachusetts Institute of Technology Langmuir (1993). Fuel Cell Yejun 32

33 Nanoporous Pt-Based Catalysts PtO 2 Nanoporous Pt 200 nm 30 nm 4Li + RuO 2 Ru:2Li 2 O Ru:2Li 2 O RuO 2 (Nanoporous) + 4Li 4Li + PtO 2 Pt:2Li 2 O Pt:2Li 2 O + 4H + Pt (Nanoporous) + 4Li + + 2H 2 O Electrochemically synthesized nanoporous Pt showed the enhanced catalytic activities. Y.-S. Hu and Y.-G. Guo et al. Max-Planck Institute Nature Mat. (2006). Fuel Cell Chunjoong 33

34 Fuel Cell Chunjoong 34

35 Nanocomposite Materials Nanocomposite Materials: - Metal nanoparticles + metal-oxide matrix - Physical, chemical, and catalytic properties are different from bulk materials. Platinum/Metal-Oxide Nanocomposite Catalysts: - Pt/WO 3, Pt/RuO 2, etc. - Enhanced catalytic activity (Physical effects and/or Catalytic effects) Sung s Group, SNU Appl. Phys. Lett. (2002). Fuel Cell Chunjoong 35

36 Fuel Cell Chunjoong 36

37 Metal Phosphate Li-Ion Battery Catalyst My Group, Angew. Chem. Int. Ed. (2003) Wang s Group, Tokyo Institute of Technology J. Catal. (1997). Hydrous FePO 4 : - Reasonable Proton Conductivity (~10-4 S/cm) - Good Acidic/Thermal Stability (Anti-Corrosion Additives) - Partial Oxidation Catalysts (CH 4 CH 3 OH) - Enhanced CO Oxidation by Bifunctional Mechanisms (Pt-CO + M-OH Pt + M + CO 2 + H + + e - ) Fuel Cell Chunjoong 37

38 Wang s Group, Tokyo Institute of Technology J. Catal. (1997). Fuel Cell Chunjoong 38

39 Pt-Fe-P-O Alloy K. E. Swider-Lyons Group, Naval Research Lab. J. Electrochem. Soc. (2004). Fuel Cell Chunjoong 39

40 Possible Abilities of FePO 4 Pt C O Fe P H O C Pt O H P O Fe O FePO 4 xh 2 O Hydrous FePO 4 : - Reasonable electron and proton conductivity - Enhanced CO oxidation by bifunctional mechanism (Pt-CO + M-OH Pt + M + CO 2 + H + + e - ) Fuel Cell Yuhong 40

41 Nanostructured Pt-FePO 4 Thin-Film Electrode Co-Sputtering System Pt FePO 4 (a) Pt (200) Fe/Pt = 0.12 Pt (111) FePO 4 Pt (111) 5 nm (111) (b) (200) Fe/Pt = 0.27 ITO-Coated Glass FePO 4 Pt (111) (220) Pt (200) (311) Metal/Metal-Phosphate Nanocomposites Control of Nanostructures (111) (200) Pt (111) B. Lee, C. Kim, Y. Park, T.-G. Kim, and B. Park Electrochem. Solid-State Lett. 9, E27 (2006). (220) (311) 5 nm Fuel Cell Byungjoo 41

42 Increased Active Surface Area 0.4 Current Density (ma/cm 2 ) Pt Pt-FePO 4 (Fe/Pt = 0.12) Pt-FePO 4 (Fe/Pt = 0.27) Potential (V) vs. NHE Shaded Area: Oxidation of hydrogen adsorbed on Pt Cyclic voltammetry in 0.5 M H 2 SO 4 at 50 mv/s Fuel Cell Byungjoo 42

43 Enhanced Methanol Oxidation 0.6 Current Density (ma/cm 2 ) Pt Pt-FePO 4 (Fe/Pt = 0.12) Pt-FePO 4 (Fe/Pt = 0.27) Increased Activity by FePO 4 /Pt Ratio Potential (V) vs. NHE Pt-FePO 4 nanocomposite electrodes: - Higher current density for methanol oxidation Increased active surface area of Pt nanophases Enhanced activity of Pt by the possible ability of FePO 4 matrix Fuel Cell Byungjoo 43

44 Steady-State Activities of Nanostructured Thin Films Current Density (ma/cm 2 ) Pt-FePO 4 (Fe/Pt = 0.27) Pt-FePO 4 (Fe/Pt = 0.12) Pt Summary Time (sec) Electrode Active surface area Pt-FePO 4 Nanocomposites: - High steady-state activity - Low decay rate As the atomic ratio (Fe/Pt) increases, the steady-state activity is enhanced. Effective transfer of protons Improved CO oxidation Current density at 0.3 V Current density at 0.3 V at 300 sec Pt-FePO 4 (Fe/Pt = 0.27) 5.7 cm μa/cm 2 53 μa/cm 2 Pt-FePO 4 (Fe/Pt = 0.12) 3.6 cm 2 70 μa/cm 2 13 μa/cm 2 Pt 2.5 cm 2 35 μa/cm 2 2 μa/cm 2 Fuel Cell Byungjoo 44

45 Iron Phosphate/Pt Thin-Film Nanostructures (b) Fe/Pt = 0.27 (111) (200) FePO 4 matrix (220) (311) Pt (200) FePO 4 Pt (111) 3 nm (111) (200) Pt (111) (220) (311) 5 nm Pt B. Lee, Ph.D. Thesis at SNU (2007) Pt active layer: ~3 layers of Pt nanoparticles Effective thickness of FePO 4 : ~10 nm Distance between Pt nanoparticles: 1-2 nm FePO 4 shows reasonable electron conductivity. B. Lee, C. Kim, Y. Park, T.-G. Kim, and B. Park Electrochem. Solid-State Lett. 9, E27 (2006). Fuel Cell Byungjoo 45

46 Suggested Mechanisms of Enhanced CO Oxidation 1. Electronic Effect O C Pt FePO 4 Reduction in density of states on the Fermi level Reduced bonding energy between CO and Pt Goodenough s Group, Univ. of Texas at Austin, Chem. Mater. (1989). Wiekowski s Group, UIUC, J. Phys. Chem. (1994). e - 2. Bifunctional Effect O H C O Metal phosphate provides active OH. Pt-CO + FePO 4 -OH Pt + FePO 4 + CO 2 + H + + e - Pt FePO 4 Watanabe s Group, Yamanashi Univ., J. Electroanal. Chem. (1975). Cairns s Group, Lawrence Berkeley Lab., J. Phys. Chem. (1993). Fuel Cell Byungjoo 46

47 Current Issues in Pt Catalysts Poor Stability during Long-Term Operation Slow Oxygen-Reduction Kinetics Easy Poisoning by Pollutants High Cost Nanostructured Catalysts - Nanocomposites - Nanoporous Materials Fuel Cell Chunjoong 47

48 Instabilities of Fuel Cells during Long-Term Operation Pristine Pt/C 10 nm % Pt Surface Area Surface Area Loss Dissolution Ostwald Ripening Loss Agglomeration Cycled Pt/C 0 Membrane Electrochemical Active Area ~10 μm Cathode Diffusion Media The Significant Electrochemical Active Area Loss: Agglomeration and Dissolution of Pt Nanoparticles 10 nm Instability of Pt/C Electrocatalysts in PEMFC Y. Shao-Horn s Group (MIT), J. Electrochem. Soc. (2005). Fuel Cell Chunjoong 48

49 Fuel Cell Chunjoong 49

50 Instability of Pt Catalysts Pt PtO PtO 2 xh 2 O Accelerated cycling in this work Pt + H 2 O PtO + 2H + + 2e - E = 0.98 V Anode On Off On Cathode Pt Pt e - E = 1.18 V V (vs. NHE) Pt Dissolution at the Cathode - Stable at a Wide Potential Range - Abrupt Potential Change at the On/Off Operation Dissolution of Pt Mathematical Model of Platinum Movement in PEM Fuel Cells UTC Fuel Cells, J. Electrochem. Soc. (2003) Pt dissolution in this work was accelerated with the repeated cycling. ( V, 500 mv/s for 1000 cycles) Fuel Cell Chunjoong 50

51 Synthesis of FePO 4 -Pt/C Nanocomposites Fe(NO 3 ) 3 9H 2 O (NH 4 ) 2 HPO 4 20 wt. % Pt/C (E-TEK Co.) Distilled Water ~ph 2 Solution Drying and Annealing FePO 4 /Pt/C Nanocomposites with Various Conditions ~15 nm 1/2O 2 + H 2 H 2 O ~2.6 nm FePO 4 Pt FePO 4 Pt FePO 4 Pt FePO 4 Carbon Surface Fuel Cell Chunjoong 51

52 Nanostructures of FePO 4 /Pt/C Nanocomposites TEM Images (220) (111) (311) (200) EDS Mapping Pt (111) Pt (200) Pt Fe FePO 4 and Pt nanoparticles are well dispersed. C. Kim, B. Lee, Y. Park, J. Lee, H. Kim, and B. Park Appl. Phys. Lett. 91, (2007). Fuel Cell Chunjoong 52

53 XPS of FePO 4 -Pt/C Nanocomposites XPS of Pt Intensity (arb. unit) Pt 0 Pt 2+ Pt 0 4f 5/2 4f 7/2 4f 7/ Binding Energy (ev) FePO 4 (0.1 mm)-pt/c FePO 4 (1 mm)-pt/c FePO 4 (10 mm)-pt/c Pt/C (FePO 4 : Pt = 1 : 1) Slight Peak Shift of Pt in FePO 4 -Pt/C Nanocomposites Zero-Valent Metallic Pt Phase Charge Transfer of Pt The Largest Interfacial Contacts in FePO 4 (0.1 mm)-pt/c Fuel Cell Chunjoong 53

54 Electrocatalytic Properties of FePO 4 /Pt/C Nanocomposites : 1 3 : 1 1 : 1 Pt/C 0.0 Current (ma/mg) : 1 5 : 1 1 : 1 Pt/C Potential (V) vs. NHE After 1000 Cycles FePO 4 /Pt ratio of 1 and 3 showed the best enhanced long-term stabilities. Current Density (ma/cm 2 ) Pt/C FePO 4 : Pt/C = 1 : 1 FePO 4 : Pt/C = 3 : 1 FePO 4 : Pt/C = 5 : 1 (FePO mm) The Decreased Loss of Electrochemical Active Area More Conserved Oxygen-Reduction Reaction Pt/C 5 : 1 3 : 1 1 : 1 Pt/C 5 : 1 3 : 1 1 : Potential (V) vs. NHE Fuel Cell Chunjoong 54

55 Agglomeration after 1000 Cycles TEM of Pt/C after 1000 cycles TEM of FePO 4 /Pt/C after 1000 cycles Initial Pt/C Agglomerated Pt Nanoparticles ( ~10 nm) 30 nm Similar Nanoparticle Size to the Initial Stage Synthetic Concentration of FePO 4 Molar Ratio (FePO 4 : Pt) Electrochemical Surface Area 1 Dissolution of Pt (at. %) 2 Pt/C 0 : 1 41% 18% 1 ESA: Measured by Hydrogen Desorption (from initial 100%) FePO 4 (0.1 mm)/pt/c 1 : 1 53% 4% 3 : 1 71% 3% 5 : 1 50% 11% 2 Dissolution into Electrolyte (by ICP) FePO 4 (1 mm)/pt/c 1 : 1 47% 6% FePO 4 (10 mm)/pt/c 1 : 1 46% 14% Fuel Cell Chunjoong 55

56 Suggested Mechanisms for Enhanced Stability I 1. Stabilization of Pt by the modification of the electronic structures due to the charge transfer with FePO 4. Au cluster Electron-poor Pt nanoparticles by Au clusters exhibited the enhanced stabilities. Stabilization of Platinum Oxygen-Reduction Electrocatalysts Using Gold Clusters R. R. Adzic s Group, Science (2007). Pt e - Au cluster Fuel Cell Chunjoong 56

57 Suggested Mechanisms for Enhanced Stability I Au cluster e - Electron-rich Au clusters showed the enhanced catalytic properties. Charging Effects on Bonding and Catalyzed Oxidation of CO on Au 8 Clusters on MgO U. Landman s Group, Science (2005). Fuel Cell Chunjoong 57

58 Suggested Mechanisms for Enhanced Stability II 2. FePO 4 nanoparticles can passivate the active paths for the agglomeration of Pt nanoparticles. Pt Agglomerates Pt nanoparticles can migrate easily through etched carbon surface and agglomerate into larger Pt. Pt Highly Oriented Pyrolytic Graphite Stability of Pt-Catalyzed Highly Oriented Pyrolytic Graphite Against Hydrogen Peroxide in Acid Solution Z. Ogumi s Group, J. Electrochem Soc. (2006). Fuel Cell Chunjoong 58

59 Stability of Pt-Catalyzed Highly Oriented Pyrolytic Graphite Against Hydrogen Peroxide in Acid Solution Z. Ogumi s Group, J. Electrochem Soc. (2006). Fuel Cell Chunjoong 59

60 Motivation: Problems of Ru Crossover Degradation of electrode performance by long-term operations: - Dissolution of noble metal-based catalysts - Agglomeration of catalyst nanoparticles For PtRu catalyst in DMFC Anode: - Ru Crossover from PtRu Anode to Pt Cathode [Zeleney s Group, Los Alamos National Lab., J. Electrochem. Soc. (2004)] Impacts of Ru Dissolution: - Methanol Oxidation - Membrane Performance - Oxygen Reduction Need to Block Ru Crossover Fuel Cell Yejun 60

61 Motivation: Ru Oxidation Potential and DMFC Operating Potential Pt(OH) 2 Ru Pt Ru(OH) 3 PtO 2 xh 2 O RuO 2 2H 2 O Ru + 3H 2 O Ru(OH) 3 + 3H + + 3e - E = V Measurement Cycling Accelerated Cycling Pt + 2H 2 O Pt(OH) 2 + 2H + + 2e - E = V DMFC Anode On Off Ru Ru e - E = V Potential (V vs. NHE) Ru dissolution of PtRu: - Abrupt high potential is applied to DMFC anode when fuel cell is turned off. [dupont Inc., J. Phys. Chem. B (2004)] Investigation of Ru dissolution in this work with the accelerated potential cycling (200 cycles, V) Ru + can be reduced within the DMFC operating-potential ranges. Fuel Cell Joonhyeon 61

62 Motivation: Metal-Phosphate Coating PtRu H + CH 3 OH O Fe P H Hydrous and Porous FePO 4 : Channel of H + and CH 3 OH P Fe P Fe PtRu H + CH 3 OH (111) (b) (200) Fe/Pt = 0.27 FePO 4 xh 2 O FePO 4 (220) (311) FePO Pt (200) 4 Pt (111) PtRu H + CH 3 OH (111) (200) Pt (111) (220) (311) My Group Fuel Cell Yejun Electrochem. Solid-State Lett. (2006) nm

63 Fuel Cell Yejun 63

64 Motivation: Change of Voltammogram due to Ru Deposition on Pt Cyclic voltammogram of Pt in Ru + -dissolved electrolyte: Spontaneous Ru deposition on Pt Kucernak s Group, Imperial College of Science Technology, J. Phys. Chem. B (2002). Ru Deposition on Pt Surface: The Loss of Pt Nature Fuel Cell Yejun 64

65 FePO 4 Coating Layer for Blocking Ru Crossover Uncoated FePO 4 -coated PtRu Electrolyte Concentration of Ru PtRu FePO 4 Electrolyte Concentration of Ru 5 nm Before 200 accelerated cycles ESA (per 1 cm 2 sample) ESA (per 1 cm 2 sample) After 200 accelerated cycles Ru dissolution into electrolyte (per 1 cm 2 sample) (normalized by ESA) Uncoated 0.60 cm cm ± 0.39 ppb/cm ± 0.65 ppb/cm 2 FePO 4 -coated (5 nm) 1.05 cm cm ± 0.44 ppb/cm ± 0.42 ppb/cm 2 FePO 4 -coated (20 nm) 1.08 cm cm ± 0.44 ppb/cm ± 0.41 ppb/cm 2 Considering exposed PtRu surface area, the dissolved Ru species were retained within FePO 4 -coated layer. Fuel Cell Yejun 65

66 Oxygen-Reduction Activity of Modified Au Catalyst Various Au/AlPO 4 nanocomposites were synthesized: ~10 nm gold crystallites were aggregated with the interposed AlPO 4. The transfer of electron density from AlPO 4 to Au: Controlling the Au catalytic activities with the modification of electronic structure. Y. Park, B. Lee, C. Kim, J. Kim, S. Nam, Y. Oh, and B. Park, J. Phys. Chem. C (2010). Fuel Cell Yejun 67

67 Conclusions Nanoscale Interface Control - Compositions? - Nanostructures? - Mechanisms?

68