Pt-free Direct Ethanol Fuell Cells

Transcription

1 Pt-free Direct Ethanol Fuell Cells Viktor HACKER, Astrid HOFER, Merit BODNER, Christoph GRIMMER, Alexander SCHENK 8 th A3PS Conference Eco-Mobility 2013 Strategies, R&D-Funding Programs and Projects of Industry, Research and Public Authorities for the Development and Market Introduction of Alternative Propulsion Systems and Fuels in cooperation with

2 Introduction ICVT Content Fundamentals Direct Alcohol Fuel Cells Advantages Applications Fuels Workings principle Celland flow fielddesignforliquid fuels Development of Pt free anode catalysts for alkaline direct ethanol fuel cells Pt-free vs. Pt catalysts Conclusion 2

3 CEET BZ V. Hacker 3

4 Direct alcohol fuel cells direct use of alcohols in fuel cells opportunity to avoid efficiency losses from fuel processing, the production of hydrogen the state of aggregation is liquid at standard conditions easier storage and handling allows further use of the traditional fuel infrastructure energy density is comparable to gasoline 4

5 simple system set up low temperatures portable applications Applications DAFC off grid power supply for electronic devices mobile phones laptops camping power outputs up to 100 W so far only DMFC systems available 5

6 Direct fuel cells 6

7 Direct fuel cells Power to Fuel Hydrogen Storage 7

8 Feedstock Sucrose containing feedstocks, Bioethanol e.g. sweetsorghum, sugarbeetand cane etc. Starchy materials, e.g. wheat, corn, potatoes etc. Lignocellulosic biomass, e.g. wood, grass, strawetc. 1 st generation about 90% of all ethanol is derived from the first two classes by fermentation, the rest is produced synthetically Highly developed fermentation processes Low sugar yield per hectare World production of bioethanol 2006: 39 billion L Estimationfor2015: 100 billionl 1. Generation Bioethanol 2. Generation Bioethanol Source: N. Sarkar, S.K. Ghosh, S. Bannerjee, K. Aikat, Renewable Energy 37 (2011)

9 2 nd generation Bioethanol Lignocellulosic materials most abundant feedstock in world No rivalry between food and fuel production Difficult conversion to ethanol 9

10 Direct Ethanol Fuel Cells H 2 + ½O 2 H 2 O Elektrolyt H 2 2 H + + 2e - 2 H + + ½O 2 + 2e - H 2 O 10

11 Direct Ethanol Fuel Cell Complex reaction mechanism Insufficient electrocatalysts 12 electrons per molecule Complete oxidation involves C-C bond breakage Pt is poisoned by reaction intermediates PtRu and PtSn catalysts High Pt loadings high performance loss Source: S. C. S. Lai and M. T. M. Koper, Faraday Discuss.,2008, 140,

12 Alkaline Direct Ethanol Fuel Cells Improved reaction kinetics of the ethanol oxidation reaction compared to the acidic cells Inexpensive metals such as Ni can be used Neutralisation reaction of OH-avoided by the use of polymer electrolytes Anion-exchange-membrane analogous to the protonexchange-membrane 12

13 Cell design for liquid fuels design of a passive and semipassive DEFC cathode: Pt/C, anode: PtRu/C, hydrocarbon type commercial membrane operation at room temperature (25+/-2 C) Ni foam as backing layer graphite composite bipolar plates grid type, single serpentine cathode: Pt/C, anode PtRu/C, both sides SSFF Voltage [V] 1,2 3, ,5 0,8 2 0,6 0,4 1 0,2 0, Current density [ma/cm²] 1,5 Power density [mw/cm²] activ passive 13

14 Direct Ethanol Fuel Cells H 2 + ½O 2 H 2 O Elektrolyt H 2 2 H + + 2e - 2 H + + ½O 2 + 2e - H 2 O 14

15 Motivation Developmentof a PGM (platinumgroupmetal) free anode catalyst for the EOR (ethanol oxidation reaction) Average price of pgmmetals, Au and Ni ( ) 15

16 Support material chemicaldeposition on 3 different types of carbon - Vulcan XC72 - thermally pretreated Vulcan XC72 - acid treated Vulcan XC72 highestpeakcurrentdensity on Au/Cox, lower onset potential on Au/Ctherm 16

17 Synthesis two phase synthesis yields in a clearly higher active surface area the start of the EOR is strongly shifted to lower potentials (0,5 V). currents from the EOR do not result in a distinct peak but in a plateau highest current density is nearly 4-fold potential range is doubled 1 ] mḡ cm A [m 0 sity n e d t-200 n re u C-400 Au/Ctherm Au/Ctherm2 0 0,5 1 1,5 1 ] 400 mḡ cm A [m 200 sity n e d 100 t n re u C 0 Au/Ctherm Au/Ctherm2 0 0,5 1 1,5-600 Potential vs. RHE [V] -100 Potential vs. RHE [V] 17

18 Bimetallic catalysts EOR on gold: - low onset potential (0,5 V) - low current densities - high stability EOR on nickel - very high onset potential (1,4 V) - high current densities bimetallic catalysts: main features of both metals remain -1 ] cm A [m 200 sity n e d t n re 100 u C -2 mg 0 AuNi/Cthermon AuNi/Ctherm2co AuNi/Ctherm2ga AuNi/Cox2co AuNi/Ctherm2on AuNi/Cox2on 0 0,5 1 1,5 2 Potential [V] 1 ] mḡ 2- cm [A sity n 200 e d t n re u 0 C -200 Au/Ctherm2 Ni/Ctherm2 AuNi/Ctherm2gal 0 0,5 1 1,5 2 Potential vs. RHE [V] limiting current densities in the potential range of 0,4 V 1,8V current densities after 20 min polarisation 18

19 Pt vs. Pt-free catalysts 19

20 High catalytic activity In both cases Pt vs. Pt-free catalysts But Pt-free catalysts: Low of density of active sites Poor stability (in acidic environment) For high energy density applications Platinum still catalyst of choice Reduction of platinum loading Platinum transition metal alloys 20

21 PtM/C cocatalysts M = Ti, V, Cr, Cu, Fe, Ni, Co Activity Improvement Pt-Pt distance Roughening d-band energy Suppression of Pt-OH ads Reduction of Platinum loading of about one third without loss of performance S. Chen, W. Sheng, N. Yabuuchi, P.J. Ferreira, L.F. Allard, Y. Shao-horn, Journal of Physical Chemistry C 113 (2009) S. Mukerjee, Journal of The Electrochemical Society 142 (1995) V. Stamenkovic, T. Schmidt, The Journal of Physical Chemistry B 106 (2002) V. Stamenkovic, B.S. Mun, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Rossmeisl, J. Greeley, J.K. Norskov, Angewandte Chemie 118 (2006) Repulsive interaction between Pt- OH und Co-O -species Cobalt acts as sacrifice element 21

22 DuraPEM - Stable and Active ORR Catalysts for HT PEMFCs A straightforward and scalable PtCo/C cocatalyst preparation method with stability increasing post-preparation treatments has been developed. Increased stability and activity of PtCo/C cocatalysts over the standard Pt/C catalysts has been achieved. Long-term operation in a HT-PEM single cell is currently in progress. 22

23 Conclusion Pt-free 23

24 Conclusion Pt-free o Ni and Au are highly active towards the catalysis of the EOR. o o o Enhancement of catalytic properties by -modification of the support material -adaption of the catalyst preparation method. Lower EOR onset potential by higher active gold surface. broader active potential range with bimetallic catalysts. 1 ] 2- mḡ cm [A sity n 200 e d t n re u 0 C -200 Au/Ctherm2 Ni/Ctherm2 AuNi/Ctherm2gal 0 0,5 1 1,5 2 Potential vs. RHE [V] o reduced EOR onset potential, higher current densities at 50% reduced gold loading. 24

25 Thank you! funded within the Austrian Klima- und Energiefonds and performed within the program NEUE ENERGIEN