Hydrogen Storage via Sodium Borohydride

Hydrogen Storage via Sodium Borohydride Current Status, Barriers, and R&D Roadmap Ying Wu Presented at GCEP – Stanford University April 14-15, 2003 Millennium Cell Inc. One Industrial Way West, Eatontown, NJ 07724

Outline

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Introduction: hydrogen storage via sodium borohydride

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Current Status: portable and vehicular applications

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Barriers to commercialization

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Research issues and on-going efforts

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Summary

Choice of Chemical Hydrides Comparison of Chemical Hydrides 20.0 %H by weight

wt% H Stored

%H in stoich. mixture w/ water

15.0 10.0 5.0 0.0

Heat of Hydrolysis Rxn (kJ/Mole H 2)

LiBH4

3

LiH

NaBH4 LiAlH4

AlH3

MgH2

NaAlH4 CaH2

NaH

0 -40 -80 -120 -160 kJ/mol H2

-200

Hydrogen Generation from Sodium Borohydride (Hydrogen (Hydrogen on on Demand™ Demand™ Process) Process)

NaBH4 + 2 H2O

à

4 H2

+

NaBO2 (aq) + ~300 kJ

cat

An energy-dense water-based fuel (i.e., 30 wt% NaBH4 holds 6.7 wt% H2)

Proprietary Pure humidified catalyst induces H2 delivered to rapid H2 engine or production fuel cell

Borate can be recycled into NaBH4

Exothermic reaction requires no heat input

Hydrogen is generated in a controllable, heat-releasing reaction Fuel is a room-temperature, non-flammable liquid under no pressure No side reactions or volatile by-products. Generated H2 is high purity (no CO, S) and humidified (heat generates some water vapour)

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Groups Investigating Borohydride and Related Systems

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Millennium Cell – Hydrogen on DemandTM Systems and SBH Synthesis; Partners: U. S. Borax, Air Products and Chemicals

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Manhattan Scientifics/R.G. Hockaday – Portable SBH systems

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Hydrogenics – System integrator, HyPORTTM power generator using SBH as source of H2

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Prof. S. Suda (MERIT/KUCEL) – Hydrogen generation method, and SBH synthesis from MgH2.

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Toyota Motor Company – Japanese patents on H2 generation from SBH, methods for SBH synthesis.

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Dr. Peter Kong, INEEL – Nuclear energy assisted synthesis of SBH, recently acquired funding

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Prof. M. A. Matthews, Univ. South Carolina – SBH hydrogen generation systems (steam hydrolysis)

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Prof. A. Zuttel, Univ Fribourg, Switzerland – LiBH4, thermo -decomposition

Volumetric Storage Efficiency Volume of SBH Fuel Solution Required To Store Varying Amounts of Hydrogen 120

Volumetric storage efficiency of 30 wt% fuel = ~63 g H2/L

Storage of 1 kg H2 110

Storage of 3 kg H2

Volume of Solution (Gallons)

100

Storage of 5 kg H2

For comparison:

Storage of 7 kg H2

90

Storage of 9 kg H2

Liquid H2 =

80

5,000 psi compressed = ~23 g H2/L

70 60

10,000 psi compressed = ~39 g H2/L

50 40

For a practical system, Balance of Plant is key

30 20 10 0 10%

15%

20%

25%

30%

SBH concentration (wt%)

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~71 g H2/L

35%

40%

Gravimetric Storage Efficiency of SBH, with BOP Calculated Hydrogen Storage Efficiency, 90% Fuel Utilization 26 Max theoretical H2 stored (100% util) (wt%)

H2 gravimetric storage density (wt%)

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10% BOP (weight)

Max theoretical

20% BOP (weight)

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30% BOP (weight)

20

40% BOP (weight)

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10% BOP wt

16

20% BOP wt

14

30% BOP wt

12

40% BOP wt

10 8 6 4 2 0

0

10

20

30

40

50

60

70

80

90

100

110

120

Stored SBH fuel concentration (wt%)

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SBH has intrinsically high storage density for H, which can yield practical hydrogen generation systems with proper engineering

TM Schematic Practical Hydrogen on DemandTM

Water from Fuel Cell

Demand TM

Fuel tank: NaBH4 solution

Fuel Hydrogen on Pump Catalyst Chamber

Gas/Liquid Separator H2

H2 Discharged fuel area: NaBO2

NaBO2

borate

H2 O Hydrogen + Steam Coolant Loop Heat Exchanger

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Pure Humidified H2 Oxygen from Air

Fuel Cell

Hydrogen on Demand™ Applications Prototype Prototype Backup Backup Power Power System System -- 1.2 1.2 kW kW hydrogen hydrogen generation generation system system

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Systems typically run at < 40 psig system pressure, rated at 18 SLM hydrogen, capable of max flows of up to ~45 SLM (~3 kWe)

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One-button operation – works as a “black box” hydrogen source that looks like a low pressure hydrogen cylinder

Commercial Vehicle Demonstrations

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Chrysler Town and Country Natrium®

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Peugeot-Citroën H2O Vehicle

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Fuel cell (Ballard Power Systems) electric hybrid minivan

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Fuel cell (Hpower) electric hybrid vehicle, fire rescue vehicle concept car

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Debut at EVAA – Dec 2001, on tour most of 2002

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Debut at Paris Auto Show – Oct 2002

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FC is ~5 kW range extender

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FC is ~60 kW primary power plant

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Estimated 300 mile range for system

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Volumetric Efficiency of Hydrogen Storage and Generation Increased Increased Packaging Packaging Flexibility Flexibility SBH Fuel/Borate Tank Electric Drive Motor

Lithium Ion Battery Pack

Hydrogen on Demand™ H2 Generator

DC/DC Converter

Ballard Fuel Cell Engine

Top View

3 cylinders @ 5000 psi

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Transportation / Stationary: Projected Target Gravimetric Gravimetric Projection Projection (50-75 (50-75 kW, kW, 7.5 7.5 kg kg stored stored H H22)) Projection: Gravimetric Storage Density 20.0

90

Stored Conc

80

System wt%

18.0

70

14.0

Need for FC water!

60

12.0

50

8.4 wt% H2

40

Next generation prototype

30

10.0 8.0

+ 50% FC Water

6.0

Pre-Natrium

20

4.0

10 0 1999

2.0

Natrium

2001

2003

2005 Year

12

16.0

75 wt% SBH fuel

2007

2009

0.0 2011

System H2 Storage Fraction (wt %)

SBH Stored Concentration (wt%)

100

Current Status of H 22 Storage Technologies Hydrogen Storage Technology

Current Volumetric Storage Density (g H 2/L)

Current Gravimetric Storage Density (wt %)

– of Storage Technology

5000 psi (350 bar)*

~12.5 g H2/L = 1.5 MJ/L

~ 2.7 wt%

Known Technology

H2 under pressure, g H2/L, Infrastructure, H2 not humidified

10000 psi (700 bar)*

~24.2 g H2/L = 2.9 MJ/L

~ 3.3 wt%

Known Technology

H2 under pressure, g H2/L, Infrastructure, H2 not humidified

Liquid*

~37.0 g H2/L = 4.4 MJ/L

~ 5.0 wt%

Known Technology

Boil Off, Infrastructure

Solid Metal Hydrides

?

?

?

Hydrogen on Demand™ NaBH4 Chemical Hydride

~> 22 g H2/L = > 2.5 MJ/L

> 4.0 wt%

H2 is not under pressure, system design, Infrastructure

*Taken from: GM Website, specifications of Hywire and HydroGen3 Vehicles: http://media.gm.com/about_gm/vehicle_tech/fuel_cell/monaco/hydrogen/index.htm http://media.gm.com/about_gm/vehicle_tech/fuel_cell/hywire/index.html 13

+ of Storage Technology

Regeneration, Fuel Handling Strategy

Hydrogen Storage Targets

HOD (NaBH4) Current SysWt% >4.0 Advanced HOD (NaBH4) SysWt% 6.2-8.4

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Taken from: Brenstoffzellen - Fahrzeuge von GM/Opel – Technik und Markteinfuehrung, Dr. G. Arnold, Jan 22-23, 2003

Increase the Gravimetric and Volumetric Energy Density l

Two main approaches: Directly increasing the fuel concentration: Physical characteristics issues Chemistry issues (e.g., max concentration in catalyst bed) Improving system design: Recycle H2-stream condensate Recycle fuel cell water Higher concentration è higher volumetric and gravimetric H2 storage

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Fuel properties and fuel chemistry are important across a range of high concentration fuels Physical properties Stability, solubility, viscosity Freezing points

⇒ A number of these issues are already being addressed at MCEL 15

Fuel Cost Reduction Why is NaBH 4 costly to produce? l

Need 4 electrons, stored in 4 B-H bonds, used to reduce H2O and form H2

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Need to combine 3 different elements + electrons + energy Na + B + H + electrons + energy (substantial entropic and enthalpic barriers)

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The complexity of the system leads to a stepwise process for SBH production.

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The NaBH4 price will always be driven by the price of primary energy

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Energy efficiency is key; any process has to be optimized to minimize wasted energy.

Particular Challenge for Transportation Applications l

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Convert a multi-component, high energy, high purity specialty chemical into an everyday commodity fuel Difficult to compete with the current cost of gasoline, but could compare favorably with other hydrogen storage technologies.

Can B22H66 be better than NaH as an Intermediate ? Existing Process

Proposed Process

1666 kJ/mol NaBH 4

Energy

Na NaH ( B ( O C H 3 )3 ) 3 3 1 0 k J / m o l N a B H4 (accounting for cell efficiency)

365 kJ/mol NaBH4 49 kJ/mol

N a B H4

B 2H 6 ( N a2 C O 3 )

?

B(OR)3 NaBO2

NaCl

Reaction Steps

• Production of Na is < 50% energy efficient • Further energy losses to convert Na to NaBH4 17

• Utilize alternative intermediate B2 H6. • Need appropriate energy input to efficiently produce B2 H6.

We are currently investigating both electrochemical and chemical pathways Thermochemical Pathway

Electrochemical Pathway l

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More efficient electrochemical synthesis of Na Direct electrochemical conversion of borate to borohydride Molten salts and/or ionic liquids as reaction medium

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Conversion of B(OR)3 to B2 H6

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Studied BCl3 to B 2 H6 as a model reaction system

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Reaction yield is key.

Anode

Inert Gas Inlet and Outlet

Cathode and Hydrogen Gas Sparger

Process Schematic

Thermocouple

ROH Glass Jar

NaBO2

A

B(OR)3

B

B2H6

H2 Na2CO3

Melt

CO2 Heating Mantle

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C

NaBH4

Infrastructure - Transportation Fueling/Recycling Strategy l

Supply and Demand Current production process is geared towards specialty chemical applications of sodium borohydride, and is expensive and inefficient. Markets such as backup power are less sensitive to fuel price; incremental process improvements can go a long way

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Infrastructure envisioned, such that borates will be recycled into borohydride at centralized facilities

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Chemistry research is targeting an improved synthesis and regeneration process that will allow SBH to become a commodity chemical. This is necessary in order to access markets such as transportation.

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Summary l

SBH has high intrinsic gravimetric and volumetric hydrogen storage density, which can yield practical hydrogen generation systems with proper engineering.

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Hydrogen on Demand™ technology has been successfully demonstrated over a wide range of hydrogen delivery flow rates and pressures.

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Studies are being carried out to integrate thermal and water management between the SBH fuel sub-system and the FC subsystem

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Progress is being made to improve current SBH synthesis technology aimed at reducing manufacturing cost.

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The path is defined, but there is certainly more work ahead of us ! Continued improvements in regeneration technology Systems design and engineering to access higher energy densities

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Research Opportunities • Hydrogen Delivery System • Intelligent controls for the fuel system. • Increase gravimetric and volumetric storage density • Advanced catalyst development and novel catalyst bed

development

• Solve the SBH cost reduction and recycling issue • Basic research in boron chemistry • Chemical engineering and chemical process development • Develop fueling infrastructure

• Integrate renewable energy sources and/or non carbon-

based energy sources 21

Thank You

Questions, comments, and further discussions, Please contact [email protected]

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