John Meynard M Tengco Akkarat Wongkaew Yunya Zhang Bahareh Alsadat Tavakoli Weijian Diao Tayloy R Garrick John W Weidner John R Monnier John R ID: 1042119
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1. Bimetallic Ru-Pt and Pt-Co fuel cell catalysts prepared by Strong Electrostatic Adsorption and Electroless DepositionJohn Meynard M. Tengco, Akkarat Wongkaew, Yunya Zhang, Bahareh Alsadat Tavakoli, Weijian Diao, Tayloy R. Garrick, John W. Weidner, John R. Monnier, John R. RegalbutoUniversity of South CarolinaACS Fall 2016 Meeting24 August 20161
2. INTRODUCTIONSUPPORTED METAL CATALYSTS- more efficient metal utilization- greater amount of active surfaceLarge Particlesatoms inside are not utilizedSmall Particlesmore metal atoms exposed (higher dispersion)2
3. - Inducing surface charge on support by adjusting pH of impregnating solution- SEA at incipient wetness is also called Charge Enhanced Dry Impregnation (CEDI)supportOHOH2+O-pH > PZCpH @ PZCpH < PZC[PtCl6]2-anionic complex[Pt(NH3)4]2+cationic complexmetal uptake (per support area)@ PZCpH > PZCpH < PZCcation uptakeanion uptakesupport[PtCl6]2-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)supportreduction treatmentPt0INTRODUCTION: STRONG ELECTROSTATIC ADSORPTION (SEA)3
4. INTRODUCTION: BIMETALLIC CATALYSTSvsUsing 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 catalystsAddition of another metal can enhance catalytic activityBimetallic EffectsBifunctionalElectronicEnsembleUsual method of co-impregnation does not ensure interaction between component metals4
5. Targeted deposition of secondary metal on the surface of primary/seed catalystImmersion of seed catalyst in ED bathActivation of reducing agent (RA) on the surface of seed catalystReduction and deposition of secondary metal Catalytic depositionAuto-catalytic deposition- Necessary to have proper combination of reducing agent, metal precursor, and ED conditionsINTRODUCTION: ELECTROLESS DEPOSITION (ED) FOR BIMETALLIC CATALYSTS5
6. Pt based catalysts for Fuel CellsDMFC:Anode Reaction: CH3OH+ H2O → CO2 + 6H+ + 6e-Cathode Reaction: 3/2O2 + 6H+ + 6e- → 3H2OCell Reaction: CH3OH+ 3/2O2 → CO2 + 2H2O6Significantly large quantities of Pt used in fuel cellsPoor dispersion gives low S.A., thus the need to increase metal loading
7. Electroless Deposition of Ru on Pt/C prepared by Strong Electrostatic Adsorption7
8. Activation of reducing agent (RA) on base catalystReduction of secondary metal on the surfaceFurther deposition of secondary metalReducing Agent: Formic Acid, HCOOHRu Precursor: Hexaammineruthenium(III) chloride, Ru(NH3)6Cl3pH condition: Acidic, below PZC of Carbon Support (8.5), to prevent adsorption of [Ru(NH3)6]3+ on carbon surface8PRIOR STUDY:BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED)T. R. Garrick, W. Diao, J. M. Tengco, J. R. Monnier and J. W. Weidner, Elec. Acta., 2016, 195, 106R. 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, 28354W. Diao, J. M. M. Tengco, J. R. Regalbuto, and J. R. Monnier, ACS Catal., 2015, 5, 5123
9. HAADF-STEMXEDS MapsPlatinumRutheniumPt@Ru/C(A)(B)(C)(D)5nm4nmRu 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 phaseTPR and XPS also confirm excellent association between component metalsRepresentative electron micrographs and elemental maps of selected spots of 0.96 ML Ru on Pt/C9PRIOR STUDY:BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on commercial 20% Pt/C catalyst
10. PRIOR STUDY:BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on commercial 20% Pt/C catalystCommercially available Ru-Pt Catalyst composition: 13.2% Pt and 6.8% RuPeak activity at 50% theoretical surface coverage (Ru/Pt = 1:1)Mass activities for Methanol Electrooxidation10
11. SEA 6.3% Pt/Carbon (Vulcan XC72R)STEM Number Average Size1.93 nmX-Ray Diffraction Size1.5 nmBASE CATALYST PREPARATION11
12. SEA 6.3% Pt/Carbon (Vulcan XC72R) vs.Commercial 20% Pt/Carbon (Vulcan XC72)20nm20nmdN = 1.9nmdXRD = 1.5nmdN = 3.1nmdXRD = 2.5nmCOMPARISON OF BASE CATALYST PREPARED BY SEA WITH COMMERCIAL CATALYST12
13. BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – on SEA prepared 6.3% Pt/C catalystRepresentative electron micrographs and elemental maps of selected spots of 0.50 ML Ru on Pt/CPtRuPtRu13
14. BIMETALLIC Pt@Ru/XC72R PREPARED BY ELECTROLESS DEPOSITION (ED) – comparison of Commercial vs SEA prepared base catalystMass activities for Methanol Electrooxidation14Peak 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 Impregnation15
16. Co/C prepared by impregnationLarge seed catalyst particlesLarge agglomerated bimetallic particlesPRIOR STUDY: Pt ED on Co/C
17. 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 1hrLoadings: 2.5% Co/CB1 and 5% Co/CB1Average particle size from XRD: 1.6nm(for both 2.5% and 5% Co/CB1)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)HAADF micrograph of 5% Co/CB1XRD profiles of Co/CB117
18. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALTCatalystPt θ(theo)Co wt %before ED(nominal)metal loading after ED (wt %)PtCo*A1.52.56.70.9B3.02.512.21.2C1.55.012.62.4D3.05.022.22.6Reducing Agent: Dimethylammineborane (DMAB)Pt Precursor: Chloroplatinic acid, H2PtCl6pH condition: basic – pH 10, above PZC of carbon support (3.7), to prevent adsorption of [PtCl6]2- on carbon surfaceEthylenediammene added to improve bath stabilityPt:DMAB:EN = 1:5:4T = 50°CTheoretical Pt coverages used:1.5ML, 3.0ML* Loss of Cobalt was observed upon immersion of catalyst in ED bathStability test, 1ML Pt (no Co/C)ED test, 1ML Pt (with Co/C)Trial deposition curves – Pt ED on Co/CB118
19. ELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALTX-RAY DIFFRACTION PROFILES OF Co@Pt/CB1 CATALYSTSPeak “shoulders” to the right of Pt peaks suggest alloy formation19Representative XRD Deconvolution
20. CatalystNominalMonodisperseCoverage of Pt (ML)Initial Coloading (%)Pt LoadingCo loadingXRDwt%atom%wt%atom%alloy (Pt-Co) phasenon-alloyed Pt size (nm)latticeparameter (Å)size(nm)A1.52.56.770.10.929.93.852.611.8B32.512.275.61.224.43.872.38.9C1.5512.661.52.438.53.852.311.0D3522.271.92.628.13.882.310.6
21. Darling, A.S., Cobalt-Platinum Alloys: A Critical Review of their Consitution and Properties. Platinum Metals Rev., 1963, 7, (3), 96-104Confirmation of Pt-Co alloy from literatureELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALTCatalystCo bulkatom %Bulkatomic Pt/CoAlloy Lattice Param. (Å)A29.92.343.85B24.43.103.87C38.51.603.85D28.12.553.8821Lattice parameter curve for the alloys quenched from 1000°CPt-Co ED samples
22. 3.0ML Pt on 5.0% Cobalt on Carbon Black 1Post-reduction at 200°C, 1 hrELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALTHAADF-STEM Micrographs22
23. 3.0ML Pt on 5.0% Cobalt on Carbon Black 1Post-reduction at 200°C, 1 hrELECTROLESS DEPOSITION OF PLATINUM ON CARBON SUPPORTED COBALTPtCoCombinedPtCoCombinedElemental (XEDS) Maps23
24. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITIONECSA of ED samples low due to large particles formed or from “carbonaceous residue” from ED process24
25. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITIONSpecific activityO2 saturated 0.1 M HClO4, 5 mV/sec, 1600 rpm, @0.9 V vs RHE. 25
26. BIMETALLIC Co@Pt/CB1 PREPARED BY ELECTROLESS DEPOSITIONMass activityO2 saturated 0.1 M HClO4, 5 mV/sec, 1600 rpm, i @0.9 V vs RHE. 26
27. SUMMARY and CONCLUSIONSSmaller, 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
28. Thank you28ACKNOWLEDGEMENTSASPIREELECTRON MICROSCOPY CENTERRegalbuto Group (SEA)Monnier Group (ED)Weidner Groupd (Electrochemistry)