Electrochemical Performance of Thin-Film Pt x Y Electrodes in PEMFC

Transcription

1 Electrochemical Performance of Thin-Film Pt x Y Electrodes in PEMFC Björn Eriksson a, Niklas Lindahl b, Björn Wickman b, Rakel Wreland Lindström a, Göran Lindbergh a, Carina Lagergren a a Applied Electrochemistry, School of Chemical Science and Engineering, KTH b Competence Centre for Catalysis, Department of Physics, Chalmers University of Technology

2 Outline Background Platinum alloy catalysts Thin film gas diffusion electrodes Method Sputter deposition Acid pretreatment Electrochemical tests Results Sputter deposition Acid pretreatment Electrochemical tests Conclusions Outlook 2

3 Pt-alloyed catalysts- Better utilization of Pt J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov, Nature Chemistry, 2009, 1,

4 Desired structure Platinum skin on top of Pt 3 Y bulk. Bulk causes strain on Pt-skin N. Lindahl, E. Zamburlini, L. Feng, H. Grönbeck, M. Escudero-Escribano, I. Stephens, I. Chorkendorff, C. Langhammer, B. Wickman, Manuscipt in preparation 4

5 Thin film gas diffusion electrodes Well defined Loading Composition Low loading Low IR-drop Low heat production Low water production Can be tested in full cell setup 5

6 Method 6

7 Sputter deposition Single target co-sputtering with Pt-target and clips of Y-foil. Composition controlled by the fraction of Y-clips on the Pttarget DC magnetron sputtering at 1.5 Å/s. Base pressure < 1.5x10-6 mbar and sputtering in 5 mtorr under 50 cm 3 /min Ar-flow. 60 nm thick catalyst sputtered onto GDL (Carbel CL) 7

8 Acid pretreatment Method: 0.1 M HClO 4 10 min 5 x rinsed with water Dried for 30 min Remove yttrium oxide from surface. Pt-skin Pt 3 Y-bulk Pt 3 Y-bulk 8

9 Cell materials Anode: 3.8 cm 2 with loading of 0.5 mg Pt/cm 2 GDE Cathode: 0.95 cm 2 with loading of 60 nm catalyst Membrane: Nafion 212 9

10 PEMFC electrochemical tests Activation 2000 cycles, V vs SHE, 20 mv/s 5 % H 2 (Ar) / O 2, 80 C Polarization 100 cycles V vs SHE, 20 mv/s 5 % H 2 (Ar) / O 2, 80 C Average of all cycles shown Cyclic voltammetry 20 cycles V vs SHE, 200 mv/s 5 % H 2 (Ar) / N 2, 30 C Last cycle shown CO-stripping 5 cycles V vs SHE, 200mV/s 0.15 V 1 min 5 % H 2 (Ar) /N 2 2 min 5 % H 2 (Ar) / 2 % CO (Ar) 5 min 5 % H 2 (Ar) /N 2 5 cycles 0.15 V-1.2 V vs SHE, 200mV/s First cycle shown 10

11 Results 11

12 SEM of sputtered films Carbel CL Pt x Y sputtered Carbel CL 12

13 Pt x Y acid treatment (XPS-data) Sample Atom % Pt (Y) Pt/Yratio I: As produced 57.1 (42.9) 1.3 II a: Acid Treatment x (9.6) 9.4 II b: Acid Treatment x (9.9) 9.1 II c: Acid Treatment x (9.8) 9.2 Normalized Intensity / a.u Y3d I IIa IIb IIc III III: Acid Treatment x2 + EC tests 94.8 (5.2) Binding Energy / ev

14 SEM analysis after acid pretreatment Pt x Y as produced Pt x Y acid pretreated 14

15 Pt x Y performance (CV) Similar size and position Current density [ma/cm 2 ] Pt -2 PtY PtY acid pretreated Potential [V] Slight decrease in oxygen-reduction peak for Pt x Y Gas: 5% H 2 (Ar) / N V, 200 mv/s, 30 C 15

16 Pt x Y performance (CO-stripping) Current density [ma/cm 2 ] Pt PtY PtY acid pretreated Similar size and position Shoulder could indicate presence of different binding energies Potential [V] Gas: 5% H 2 (Ar) / N 2 / 2% CO (Ar) V, 200 mv/s, 30 C 16

17 Pt x Y performance (mass basis) Potential [V] Pt PtY PtY acid pretreated Higher activity for both Pt x Y samples Mass determined from the deposited amount Current/(mass Platinum) [A/mg Pt ] Gas: 5% H 2 (Ar) / O V-0.3 V, 20 mv/s, 80 C 17

18 Pt x Y performance (ECSA basis) Potential [V] Pt PtY PtY acid pretreated Higher activity for acid pretreated sample ECSA determined from COstripping Current/ECSA [A/cm 2 ] Pt Gas: 5% H 2 (Ar) / O 2 0.9V-0.3V, 20mV/s, 80 C 18

19 Conclusions Successful fabrication of thin film Pt x Y electrodes Acid treatment allows for correct surface structure Successful testing in PEMFC full cell setup Higher activity than pure Pt electrodes ~3 higher at 0.8 V (Mass basis) ~1.7 higher at 0.8 V (ECSA basis) 19

20 Outlook Further characterization of surface and composition Test additional Pt/Y ratios Test stability of PtY electrodes 20

21 Acknowledgments FFI - Strategic Vehicle Research and Innovation STandUp for ENERGY The Danish Council for Strategic Research Knut and Alice Wallenberg Foundation 21