Fuel cells, myths and facts. PhD candidate Ole-Erich Haas

Transcription

1 Fuel cells, myths and facts PhD candidate Ole-Erich aas 1

2 Outline Fuel cell, history and general principle Fuel cell types and chemical systems PEM fuel cells for transport sector Polymer membranes Electrodes and catalysts Myths 2

3 Fuel cell history, new or old? Mond & Langer [coined Fuel Cell] SOFC Westinghouse MCFC Broes & Ketelaar William Grove AFC Bacon PEMFC PAFC GE s Membrane FC DMFC s 1930 s 1950 s 1970 s Now

4 Fuel cells general principle Fuel cells convert chemical energy to electric energy and heat Combination of internal combustion engine and battery More efficient than combustion, due to higher energy grade > 4

5 Fuel cells general principle e - e - Unused Fuel Out Oxidant In Electron production Electron consumption 5 Fuel In Anode Electrolyte Cathode Unused Oxidant Out

6 Fuel cell types and chemical systems Fuel Cell Type Common Electrolyte Operating Temp. C Fuel Applications Advantages Power Density Alkaline (AFC) Aqueous solution KO Pure 2 Military Space Fast electrode reactions, can use several catalysts igh 6 UTC, 12 kw stack

7 Fuel cell types and chemical systems Fuel Cell Type Common Electrolyte Operating Temp. C Fuel Applications Advantages Power Density Phosphoric Acid (PAFC) Phosphoric acid in a SiC matrix Stationary power production Improved CO tolerance, long lifetime Low kw UTC PureCell 200, installed power stations, PAFC

8 Fuel cell types and chemical systems Fuel Cell Type Common Electrolyte Operating Temp. C Fuel Applications Advantages Power Density Molten Carbonate (MCFC) Liquid solution of, Li, Na, K carbonates Reform ing of fossil fuel 2 Large power stations, continuous power CO tolerant, many fuels, high temperature waste heat, high CP eff. Low kw hybrid, MCFC

9 Fuel cell types and chemical systems Fuel Cell Type Common Electrolyte Operating Temp. C Fuel Applications Advantages Power Density Solid Oxide (SOFC) Yttria stabilized zirconia Reforming of fossil fuel 2 Large power stations, continuous power CO tolerant, many fuels, high temperature waste heat, high CP eff. Medium kw hybrid, SOFC

10 Fuel cell types and chemical systems Fuel Cell Type Common Electrolyte Operating Temp. C Fuel Applications Advantages Power Density Polymer Electrolyte Membrane (PEM) Solid organic polymer Transportation Power backup systems Low temperature, high power density, quick start-up ighest kw (134 hp) onda FCX Clarity

11 PEM Fuel cell for transport sector Reduce dependence of fossil fuels Use PEM fuel cell to open for 2 11

12 ydrogen economy Where does 2 come from? 2 from natural gas Shift to electrolysis Fossil fuels 85% of current world energy, IEA Must invest in renewable energy sources 12 wind hydro geo

13 PEM Fuel cell for transport sector Fuel cell system closest to our everyday life Introduced in transport sector to reduce dependence on fossil fuel 13

14 PEM Fuel Cell for transport sector ow conversion of chemicals happen Transport in the electrodes Transport in the catalyst layer, membrane Water management 14

15 PEM Fuel Cell for transport sector Important improvements: Membranes with better stability, conductivity, water, temperature Catalyst, higher surface area, activity, stability Support materials, conductivity, stability, water transport Meet targets for lifetime, stationary, 5000 transport 15

16 Status of PEM technology Polymer membranes, mechanical strength Lifetime under cyclic conditions, about 2000 h Degrade by swelling and chemical degrading Support materials, chemically stabilized Micromoulds, Nafion 112 Swelling/drying cycles 3 times less degradation 16

17 Status of PEM technology Polymer membranes, mechanical strength Fluorine release used as measure of degradation 3 membranes in the same test, Nafion as the reference Improvements in stability from different approaches 17

18 Status of PEM technology Electrodes and catalyst, Pt on Carbon Lifetime of the catalyst layer mainly related to the growth of Pt particles and carbon corrosion Pt stable under 0.7 V Startup/shutdown, above 0.7 V Pt dissolves Migrates to membrane Redeposit on larger Pt particles 18

19 Status of PEM technology Catalysts, Progress New alloys increase stability of catalyst, Co, Au, Ni, Cr, Ir Improved catalyst stability 19

20 Status of PEM technology Electrodes and catalyst, Pt on Carbon Lifetime of the catalyst layer mainly related to the growth of Pt particles and carbon corrosion C stable under 0.7 V Startup/shutdown, above 0.7 V C corrodes, CO 2 Reduced conductivity Catalyst layer and electrode 20

21 Status of PEM technology Electrode material, Progress Support stability increase New materials Pretreatments 21 Improved support stability

22 Status of PEM technology Overall issues of PEM fuel cells More expensive than competing technologies Actual price depends on production numbers Lifetime lower than competing technology Need research on lifetime issues, performance is good 22 - P. Mock, Journal of Power Sources, 190, (2009),

23 Status of PEM technology Why keep on trying? Research improves technology each year Prototypes are closing in on targets New technology chosen when its better Also climate crisis and energy crisis urges progress/change 23

24 24 Let s go mythbusting!!

25 Myth #1, not enough Platinum? World Platinum resources The lucky few metric tones Pt ow many fuel cell cars can we make? 25

26 Myth #1, not enough Platinum? World Platinum resources The lucky few metric tones Pt ow many fuel cell cars can we make? Given, 90 kw with 45 g Pt, 1 billion cars or 1.7 times today's number 26

27 Myth #1, not enough Platinum? World Platinum resources The lucky few metric tones Pt Given, 90 kw with 45 g Pt, 1 billion cars or 1.7 times today's number Some remarks Pt in car catalyzers all ready What about Pt production Few countries have reserves Should research alternatives 27

28 Myth #1, not enough Platinum? World Platinum resources The lucky few Given, 90 kw with 45 g Pt, billion cars or 1.73 times today's number 28

29 Myth #2, batteries are better! Batteries or Li-ion, do not 2 Easy transport of electrons compared to 2 Less energy lost to surroundings 29

30 Myth #2, batteries are better! Yes, but what about Carries oxidizer, heavy Low energy density, long charging time Low lifetime, 5 years, Tesla Motors igh cost, $/kw 5kWh pack in 1 billion cars use 25% Lithium found in few countries, limited reserves? 30

31 Myth #2, batteries are better! Yes, but no.. In price and performance PEMFC is leading Both technologies needs further research Similar problems regarding Pt and Li reserves Combination seems best, ybrids So, the myth that Batteries are better! 31

32 Myth #3, not limited by the Carnot cycle Statement found in many text books Fuel cells above the law? Maximum efficiency of a heat engine η E.. T = T T L T Q W Q L T L 32

33 Myth #3, not limited by the Carnot cycle Statement found in many text books What does it mean? Maximum efficiency of a heat engine 1st law W = Q Q L 2nd law Q QL 0 = P T T L E.. S T Q W Q L T L 33

34 Myth #3, not limited by the Carnot cycle Statement found in many text books What does it mean? Maximum efficiency of a heat engine 1st law 2nd law E.. Q QL = 0 = P L T T W Q Q If we consider a Thermal Energy Reservoir Q 1st law 2nd law TER Q Δ S + 0 = P T TER... = Δ T. E. R. L. E. S S 2 +1/2O 2 Q T Q Q L 2 O W T L 34

35 Myth #3, not limited by the Carnot cycle 1st law E.. W = Q QL 2nd law (1) Q QL. E. 0 = PS T T (2) L 2 +1/2O 2 If we consider a Thermal Energy Reservoir Q Q 1st law 2nd law T 2 O TER... = Δ (3) TER Q T. E. R. Δ S + 0 = P (4) S T Q Now we can express the efficiency η E.. W = = Q Q Q Q L (5) And from (2) and (4): W 35 Q Q = P it E.. L S L T ( TER... ) Q = P +ΔS it S (6) (7) T L Q L

36 Myth #3, not limited by the Carnot cycle 1st law 2nd law E.. Q QL. E. = 0 L (1) = PS (2) T T W Q Q If we consider a Thermal Energy Reservoir 1st law Q 2nd law (3) TER Q T E R Δ S + 0 = P (4) S T TER... =Δ... Now we can express the efficiency W Q QL ηe.. = = Q Q (5) Inserting (7) in to (6): Q Q = P it E.. L S L T ( TER... E..) L ( TER... ) Q = P +ΔS it (6) (7) S Q = P +ΔS P i T (8) L S S L 2 +1/2O 2 Q T Q Q L T L 2 O W 36

37 Myth #3, not limited by the Carnot cycle Now we can express the efficiency W Q QL ηe.. = = Q Q (5) Inserting (7) in to (6): Q Q = P it E.. L S L T ( TER... E..) L S S L ( TER... ) Q = P +ΔS it (6) (7) S Q = P +ΔS P i T (8) Inserting (8) in to (5): η E.. TER... E.. ( ) Q T Δ S+ P P L S S = (9) Q If this is ideal processes: P = P = 0 TER... E.. S S 2 +1/2O 2 Q T Q Q L T L 2 O W 37

38 Myth #3, not limited by the Carnot cycle Inserting (7) in to (6): ( TER... E..) Q = P +ΔS P i T (8) L S S L Inserting (8) in to (5): η E.. TER... E.. ( ) Q T Δ S+ P P L S S = (9) Q If this is ideal processes: P TER... E.. S S = P = 0 And we get: 2 +1/2O 2 Q T Q 2 O W 38 η η E.. E.. Q T ΔS Since: Q L = Q Δ T ΔS ΔG Δ Δ L = = =Δ Which is the same expression we have for PEMFC s T L Q L

39 Myth #3, not limited by the Carnot cycle eat engine and PEMFC thermodynamic efficiencies η η FC.. FC.. T TL = = = T 3802 ΔG / J / g = = = Δ / J / g 2 +1/2O 2 Q T 2 O Q W Q L T L 39

40 Myth #3, not limited by the Carnot cycle eat engine and PEMFC thermodynamic efficiencies η η FC.. FC.. T TL = = = T 3802 ΔG / J / g = = = Δ / J / g 2 +1/2O 2 Q T 2 O Q W Q L T L 40

41 Fuel cells, summary Fuel cells have the possibility to reduce CO 2 emmisions Fuel cells need more research to improve Main focus should be on lifetime issues There is much to be done.. 41

42 Fuel cells, summary Thank you for your attention! 42