Hydrogen, fuel cells, batteries, super capacitors, and hybrids

5/13/2014
Hydrogen, fuel cells, batteries, super capacitors,
and hybrids
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The hydrogen economy
Premise: H2 + O2  H2O LHV = 120 MJ/kg (33.3 KW-hr/kg)
• Energy production via combustion or fuel cell • No green house gas; clean
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The hydrogen economy

Source of hydrogen

Fossil fuels (coal, oil, natural gas, …)

Thermochemical conversion with carbon sequestration

H2

Electricity generated from renewables (Solar, wind, hydro)

Electrolysis (50-85% efficient)
Advanced methods • Algae H2 production • Photo-electrochemical water splitting

Current production (without CO2 sequestration):  48% from natural gas, 30% from oil, 18% from coal, 4% from electrolysis
Usage:  Half for producing ammonia to be used for fertilizers; remaining for petroleum refining 3
(hydro-cracking)

Transportation Fuels

Fuels

Density LHV/mass* LHV/Vol.**

LHV/Vol. of Stoi.Mixture @1 atm,300K

Gasoline Diesel

(Kg/m3) 750 810

(MJ/Kg) 44 42

(MJ/m3) 3.3x104 3.4x104

(MJ/m3) 3.48 3.37

Natural Gas

@1 bar

0.72

45

@100 bar

71

LNG (180K, 30bar) 270

Methanol Ethanol

792

20

785

26.9

3.2x101(x) 3.2x103 1.22x104
1.58x104 2.11x104

3.25
3.19 3.29

Hydrogen

@1bar

0.082

120

@100 bar

8.2

Liquid (20K, 5 bar) 71

0.984x101(x) 0.984x103 8.52x103

2.86

*Determines fuel mass to carry on vehicle

**Determines size of fuel tank

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***Determines size of engine

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The hydrogen economy
(H2 as transportation fuel)
Obstacles
• Storage: Low energy density; need compressed or liquid H2
– Compressing from 300oK, 1 bar to 350 bar, ideal compressor work = 16% of LHV; practical energy required upwards of 35% of LHV
– Liquefaction (20oK, 1 bar LH2) work required is upwards of 60% of LHV*

5.6 kg of H2 ~700 MJ
Fuel tank capacity of 50 kg carries ~2200 MJ

Source: Argonne National Lab

CcH2: cryogenic compressed LH2
cH2: compressed H2
MOF: Metal organic framework for LH2

• Infra structure: Supply, safety, …
The hydrogen economy has significant hurdles 5
*Value adopt from NREL/TP-570-25106

What is a fuel cell?

Direct conversion
of fuel/oxidant to
electricity Fuel – Example: 2H2 + O2  2H2O
– Potentially much higher efficiency than IC engines

H2 - O2 system

i

4e- 4H+ 4e-

O2

2H

O2

2
2H2O

Porous Anode Electrolyte
Porous Cathode

excess H2

H2O + excess
O2
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History of Fuel Cell
• Sir William Grove demonstrated the first fuel cell in 1839 (H2 – O2 system)
• Substantial activities in the late 1800’s and early 1900’s – Theoretically basis established
 Nerst, Haber, Ostwald and others
• Development of Ion Exchange Membrane for application in the Gemini spacecraft in the 1950/1960 – W.T. Grubb (US Patent 2,913,511, 1959)
• Development of fuel cell for automotive use (1960s to present)

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The Grove Cell (1839)
• Important insights to fuel cell operation
– H2-O2 system (the most efficient and the only practical system so far)
– Platinum electrodes (role of catalyst)
– recognize the importance of the coexistence of reactants, electrodes and electrolyte
W.R.Grove, ‘On Gaseous Voltaic Battery,” Pil. Mag., 21,3,1842 As appeared in Liebhafsky and Cairns, Fuel Cells and Fuel Batteries, Wiley, 1968
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The coal/air cell

Wilhelm Ostwald (1894)
“The way in which the greatest of all industrial problems – that of providing cheap energy – is to be solved, must be found by electrochemistry”
Status at 1933
• Low efficiency and contamination of electrodes doomed direct coal conversion

The 1896 W.W.Jacques large carbon cell (30KW)
Picture and quote from Liebhafsky and Cairns, Fuel Cells and Fuel Batteries, Wiley, 1968

Critical processes

• Reactions (anode and cathode)
 Pre-electrochemical chemical reaction  Electrochemical reaction  Post-electrochemical chemical
reaction

Cathode of H2/O2 cell

• Transport

Ions

 Transport of ions in electrolyte

 Fuel/oxidant/ion/electron transport at

electrodes

• Role of the electrolyte

Electrolyte

 To provide medium for

electrochemical reaction

 to provide ionic conduction and to resist electron conduction
 separation of reactants

Electric Current

Porous Catalytic Electrode

Oxygen Water

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Types of fuel cell
• Classification by fuel – Direct conversion
Hydrogen/air (pre-dominant) Methanol/air (under development)
– Indirect conversion
reform hydrocarbon fuels to hydrogen first
• Classification by charge carrier in electrolyte
H+, O2- (important difference in terms of product disposal)
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Types of fuel cell (cont.)

• By electrolyte

– Solid oxides: ~1000oC – Carbonates: ~600oC

High temperature fuel cells are more tolerant of CO and other deactivating agents

– H3PO4: ~200oC – Proton Exchange Membrane (PEM): ~80oC

Automotive application
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PEM
Nafion (a DuPont product)
Tetrafluoroethylene based copolymer

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Sulfonic acid group supplies the
proton
Function:
• As electrolyte (provide charge and material carrier) • As separator for the fuel and oxidant

Retail ~$300/m2

• PEM must be hydrated properly

If dry, resistance increase; eventually crack and reactants leak through

Excess water formation: flood electrodes; prevent reactants from

reaching electrode

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Air Single H2 cell
H2O details

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Modern PEM fuel cell stack

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Voltage(V); Power density(W/cm2);Efficiency

(From 3M web site)

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Current PEM H2/O2 Fuel Cell Performance

Activation loss

+Ohmic loss

1

Theoretical potential 1.23V
+diffusion loss

0.8

0.6

Efficiency

0.4

Power density

Output Voltage

0.2 00

Output voltage with CO poisoning
0.2 0.4 0.6 0.8 1 1.2 1.4 Current density (A/cm2)

Note: Efficiency does not include power required to run supporting system 16

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Fuel cell as automotive powerplant

• Typical fuel cell characteristics

– 1A/cm2, 0.5-0.7 V operating voltage

– 0.5-0.7 W/cm2 power density

– stack power density 0.7 kW/L

– System efficiency ~50%

– $500/kW
DOE goal $35/KW at 500,000 per year production compared to passenger car at $15-20/kW

– Platinum loading ~0.3 mg/cm2

30g for a 60kW stack (Jan., 2014 price ~$1500)

(automotive catalyst has ~2-3g)

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$ per troy ounce

Price of platinum
2500
Platinum spot price
2000
(1 troy ounce = 31.1 gram)
1500 1000
500 0
18 http://www.platinum.matthey.com/pgm-prices/price-charts/
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Jan‐92 Jan‐93 Jan‐94 Jan‐95 Jan‐96 Jan‐97 Jan‐98 Jan‐99 Jan‐00 Jan‐01 Jan‐02 Jan‐03 Jan‐04 Jan‐05 Jan‐06 Jan‐07 Jan‐08 Jan‐09 Jan‐10 Jan‐11 Jan‐12 Jan‐13 Jan‐14

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The Hydrogen problem:
Fundamentally H2 is the only feasible fuel in the foreseeable future
• Strictly, hydrogen is not a “fuel”, but an energy storage medium – Difficulty in hydrogen storage – Difficulty in hydrogen supply infra structure
• Hydrogen from fossil fuel is not an efficient energy option
• Environmental resistance for nuclear and hydroelectric options
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The hydrogen problem: H2 from reforming petroleum fuel

Hydrocarbon

Air

Catalyst

Catalyst Fuel Cell Electricity

Air

H2

H2

N ,CO

CO

CO2

2

2

H2O

Note: HC to H2/CO process is exothermic;

energy loss ~20% and needs to cool stream

(Methanol reforming process is energy neutral, but

energy loss is similar when it is made from fossil fuel)

Current best reformer efficiency is ~70%

Problems:

CO poisoning of anode

Sulfur poisoning

Anode poisoning requires S<1ppm

Reformer catalyst poisoning requires S<50ppb

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