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INTRODUCTION

Bimetallic Ru-Pt and Pt-Co fuel cell catalysts prepared by Strong Electrostatic Adsorption and Electroless Deposition.

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INTRODUCTION

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  1. Bimetallic Ru-Pt and Pt-Co fuel cell catalysts prepared by Strong Electrostatic Adsorption and Electroless Deposition John Meynard M. Tengco, AkkaratWongkaew, Yunya Zhang, BaharehAlsadatTavakoli, WeijianDiao, Tayloy R. Garrick, John W. Weidner, John R. Monnier, John R. Regalbuto University of South Carolina AIChE 2016 Meeting 14 November 2016

  2. INTRODUCTION SUPPORTED METAL CATALYSTS- more efficient metal utilization - greater amount of active surface Small Particles more metal atoms exposed (higher dispersion) Large Particles atoms inside are not utilized

  3. INTRODUCTION: STRONG ELECTROSTATIC ADSORPTION (SEA) - Inducing surface charge on support by adjusting pH of impregnating solution - SEA at incipient wetness is also called Charge Enhanced Dry Impregnation (CEDI) anion uptake support pH > PZC O- [Pt(NH3)4]2+ cationic complex cation uptake pH @ PZC OH metal uptake (per support area) [PtCl6]2- anionic complex pH < PZC OH2+ @ PZC pH > PZC pH < PZC support reduction treatment Pt0 [PtCl6]2- support H2O - resulting close packed monolayer of ionic complex (retaining hydration sheaths) with strong interaction with support - decreased mobility of metal atoms result in smaller catalyst particles (compared to simple impregnation)

  4. INTRODUCTION: BIMETALLIC CATALYSTS • Addition of another metal can enhance catalytic activity • Bimetallic Effects • Bifunctional • Electronic • Ensemble • Usual method of co-impregnation does not ensure interaction between component metals vs Using a method that synthesizes a bimetallic catalyst with the required high degree of metal 1 – metal 2 interaction, such as Electroless Deposition can result in better catalysts

  5. INTRODUCTION: ELECTROLESS DEPOSITION (ED) FOR BIMETALLIC CATALYSTS • Targeted deposition of secondary metal on the surface of primary/seed catalyst Immersion of seed catalyst in ED bath Activation of reducing agent (RA) on the surface of seed catalyst Reduction and deposition of secondary metal Catalytic deposition Auto-catalytic deposition - Necessary to have proper combination of reducing agent, metal precursor, and ED conditions

  6. Pt based catalysts for Fuel Cells DMFC: Anode Reaction: CH3OH+ H2O → CO2 + 6H+ + 6e- • Cathode Reaction: 3/2O2 + 6H+ + 6e-  → 3H2O • Cell Reaction: CH3OH+ 3/2O2 → CO2 + 2H2O • Significantly large quantities of Pt used in fuel cells • Poor dispersion gives low S.A., thus the need to increase metal loading

  7. Electroless Deposition of Ru on Pt/C prepared by Strong Electrostatic Adsorption

  8. PRIOR STUDY: BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) Reduction of secondary metal on the surface Activation of reducing agent (RA) on base catalyst Further deposition of secondary metal Reducing Agent: Formic Acid, HCOOH Ru Precursor: Hexaammineruthenium(III) chloride, Ru(NH3)6Cl3 pH condition: Acidic, below PZC of Carbon Support (8.5), to prevent adsorption of [Ru(NH3)6]3+ on carbon surface T. R. Garrick, W. Diao, J. M. Tengco, J. R. Monnier and J. W. Weidner, Elec. Acta., 2016, 195, 106 R. P. Galhenage, K. Xie, W. Diao, J. M. M. Tengco, G. S. Seuser, J. R. Monnier and D. A. Chen, Phys. Chem. Chem. Phys., 2015, 17, 28354 W. Diao, J. M. M. Tengco, J. R. Regalbuto, and J. R. Monnier, ACS Catal., 2015, 5, 5123

  9. PRIOR STUDY: BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on commercial 20% Pt/C catalyst Representative electron micrographs and elemental maps of selected spots of 0.96 ML Ru on Pt/C HAADF-STEM XEDS Maps (C) (D) (A) (B) Pt@Ru/C Ruthenium Platinum 4nm 5nm Ru deposited is in good association with Pt on the surface (Ru and overlaid maps show a “shell”) XRD does not show alloy formation or large Ru phase TPR and XPS also confirm excellent association between component metals

  10. PRIOR STUDY: BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on commercial 20% Pt/C catalyst Mass activities for Methanol Electrooxidation Commercially available Ru-Pt Catalyst composition: 13.2% Pt and 6.8% Ru Peak activity at 50% theoretical surface coverage (Ru/Pt = 1:1)

  11. BASE CATALYST PREPARATION SEA 6.3% Pt/Carbon (Vulcan XC72R)

  12. COMPARISON OF BASE CATALYST PREPARED BY SEA WITH COMMERCIAL CATALYST 20nm Commercial 20% Pt/Carbon (Vulcan XC72) SEA 6.3% Pt/Carbon (Vulcan XC72R) vs. 20nm dN = 1.9nm dXRD = 1.5nm dN = 3.1nm dXRD = 2.5nm

  13. BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on SEA prepared 6.3% Pt/C catalyst Representative electron micrographs and elemental maps of selected spots of 0.50 ML Ru on Pt/C Pt Ru Pt Ru

  14. BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – comparison of Commercial vs SEA prepared base catalyst Mass activities for Methanol Electrooxidation Peak activity, same, at 50% theoretical surface coverage (Ru/Pt = 1:1)

  15. Electroless Deposition of Pt on Co/C prepared by modified Charge Enhanced Dry Impregnation

  16. PRIOR STUDY: Pt ED on Co/C • Co/C prepared by impregnation • Large seed catalyst particles • Large agglomerated bimetallic particles

  17. COBALT SEED CATALYST PREPARATION USING CHARGE ENHANCED DRY IMPREGNATION (CEDI) CEDI method is based on SEA but carried out at incipient wetness (pore filling condition and no excess liquid) Dry Impregnation of Cobalt nitrate with Citric acid on Carbon Acethylene Black (CB1, PZC=3.4) Annealing in He at 250°C for 4hrs, Reduction at 400°C for 1hr Loadings: 2.5% Co/CB1 and 5% Co/CB1 Average particle size from XRD: 1.6nm (for both 2.5% and 5% Co/CB1) HAADF micrograph of 5% Co/CB1 XRD profiles of Co/CB1

  18. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALT Trial deposition curves – Pt ED on Co/CB1 Reducing Agent: Dimethylammineborane (DMAB) Pt Precursor: Chloroplatinic acid, H2PtCl6 pH condition: basic – pH 10, above PZC of carbon support (3.7), to prevent adsorption of [PtCl6]2- on carbon surface Ethylenediammeneadded to improve bath stability Pt:DMAB:EN = 1:5:4 T = 50°C Theoretical Pt coverages used: 1.5ML, 3.0ML Stability test, 1ML Pt (no Co/C) ED test, 1ML Pt (with Co/C) * Loss of Cobalt was observed upon immersion of catalyst in ED bath

  19. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALT X-RAY DIFFRACTION PROFILES OF Co@Pt/CB1 CATALYSTS Representative XRD Deconvolution Peak “shoulders” to the right of Pt peaks suggest alloy formation

  20. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALT Confirmation of Pt-Co alloy from literature Lattice parameter curve for the alloys quenched from 1000°C Darling, A.S., Cobalt-Platinum Alloys: A Critical Review of their Consitution and Properties. Platinum Metals Rev., 1963, 7, (3), 96-104 Pt-Co ED samples

  21. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALT • 3.0ML Pt on 5.0% Cobalt on Carbon Black 1 • Post-reduction at 200°C, 1 hr HAADF-STEM Micrographs

  22. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALT • 3.0ML Pt on 5.0% Cobalt on Carbon Black 1 • Post-reduction at 200°C, 1 hr Elemental (XEDS) Maps Pt Co Pt Co Combined Combined

  23. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITION • ECSA of ED samples low due to large particles formed or from “carbonaceous residue” from ED process

  24. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITION Specific activity O2 saturated 0.1 M HClO4, 5 mV/sec, 1600 rpm, @0.9 V vs RHE.

  25. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITION Mass activity O2 saturated 0.1 M HClO4, 5 mV/sec, 1600 rpm, i @0.9 V vs RHE.

  26. SUMMARY and CONCLUSIONS Smaller, well dispersed, bimetallic nanoparticles of Ru and Pt were made by Electroless Deposition of Ru on Pt/C prepared by Strong Electrostatic Adsorption. Alloyed platinum-cobalt particles have been made by ED of Pt on carbon supported Co. Both ED prepared Ru-Pt and Pt-Co systems show enhanced activity for fuel cell applications. Electroless Deposition is a simple and viable method for the preparation of Bimetallic Catalysts. Coupled with Strong Electrostatic Adsorption, well dispersed bimetallic catalysts can be made.

  27. ACKNOWLEDGEMENTS Regalbuto Group (SEA) Monnier Group (ED) Weidner Groupd (Electrochemistry) ELECTRON MICROSCOPY CENTER ASPIRE Thank you

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