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Development and characterization of porous silicon based methanol-nitric fuel cell prototype systems for portable military applications

Tsali Cross Ph.D. JJ Kingsley Ph.D. Derek Reiman Chris D’Couto Ph.D. 11th Electrochemical Power Sources R&D Symposium, July 16, 2009


Outline

Ì Ì Ì Ì

Background • Air-free/Air-limited applications for fuel cells • Limitations of PEM fuel cells • Neah’s differentiated solution Neah’s fuel cell chemistry • Single cells performance ƒ Temperature, Concentration, and Chemistry

Neah’s fuel cell system • Demonstrator unit: multiple single cells ƒ Fabrication and performance ƒ Closed loop operation

Summary


Air-free/Air-limited Applications Ì

Submarines:

• • •

Ì

Oxygen is the most precious commodity Limited air supply for life support and buoyancy control ƒ oxygen is produced electrochemically or carried in tanks.

Power supplied by: Diesel Engine, Batteries, Nuclear Energy ƒ PEM Fuel cells: Liquid oxygen and H2/methanol/metal hydride o Siemens, Ballard, Germany, Canada, Italy, Greek, S. Korea o http://www.industry.siemens.de/data/presse/docs/m1isfb07033403e.pdf

Mines:

• • • •

Air and air quality are limited. Accidents and CO release Diesel engines are typically used (pollution) NETL: Use of Hydride fuel cells for transportation ƒ http://www.netl.doe.gov/KeyIssues/mining/phase2.pdf ƒ These fuel cells still need O2 for cathode reduction.


PEM Fuel Cells-Limitations

Ì Ì Ì Ì Ì Ì Ì Ì

Requires O2/air Limited protonic conductivity Humidity and hydration requirements Methanol crossover and poisoning in DMFCs Limited surface area in MEAs Flooding issues Expensive components (GDLs, membranes, catalysts) Manufacturability for commercialization


NEAH Fuel Cell Technology Solution Ì

Silicon-based, DMFC

• Porous silicon electrode structure • Circulating liquid streams of fuels/oxidant with electrolyte

Ì Ì Ì Ì Ì

ƒ

Proton conductivity: Not an issue (100’s of mS/cm)

ƒ

Cross-over: Addressed by FC chemistry, electrode catalysts, clean-cycles etc.

Stable, long-lasting materials Increased power density Leverage silicon manufacturing infrastructure Easily customizable Lego design Replaceable cartridges (in-loop/off-site regeneration)


Neah’s Processed Electrode


PEM DMFC vs. Neah DMFC Fuel

Electrolyte (PEM)

Catalyst

Air Technology

Proton Exchange Membrane FC

Power Density Challenges Operating Environment Manufacturability IP & Patents

Fuel & Electrolyte

Porous Si

60 – 80 mW/cm2

Ink Layer

Oxidant & Electrolyte

Porous Silicon FC 100-200 mW/cm2 (RT-60◦C)

Air breathing, drying, flooding

Balance of Plant

Air only

Air and No – air

Custom infrastructure

Si and EMS outsourcing

Diffuse, overlapping

Clear, unique* * - 11 US, 12 non-US, 6 pending US 7


Porous Si Electrodes Ì

Porous Si processes: • Anodic Etch • DRIE • Pursuing KOH

Ì

Porous Si sizes: • 4” and 6” Diameter platform • Diced to 30mm or 43mm electrodes

Ì

Anodic Etch: 15 µm pores, 5 µm spacing 3D surface area ~900 cm2

Electrode processing

Electrolytic deposition ƒ ƒ

Gold (Anode and Cathode) Pt/Ru (Anode)

Ink barrier preparation ƒ ƒ

Pt black suspension (Cathode) Au flash layer

DRIE: 40 µm pores,10 µm spacing 3D surface area ~300 cm2


Neah Power DMFC Manufacturing Model Dual supplier / outsourced manufacturing

OEM Fuel Cell Systems

Si Substrate Production

Si Electrode Production

Cell / Stack Assembly

Assembly & Test

IceMoS / Tronics

(Neah)

(Aspen / Tronics)

(SanminaSCI/Synapse)


Neah’s Fuel Cell Chemistry CH 3 OH + H 2 O → CO 2 + 6 H + + 6e −

At the Anode:

E 0 = 0.04V

• Exhibits considerable over potential • CO poisoning possible

HCOOH → CO2 + 2 H + + 2e −

E 0 = −0.17V

• less over potential compared to CH3OH • CO poisoning unlikely or rare At the Cathode:

3HNO3 + 6 H + + 6e − → 3HNO 2 + 3H 2 O

Theoretical Cell Voltages:

Catholyte Regeneration In Closed-loop:

Methanol-Nitric Chemistry:

0.9V

Formic-Nitric Chemistry:

1.1V

E 0 = 0.94V

Hydrogen peroxide addition

HNO2 + H 2 O2 → HNO3 + H 2 O Concentrated Nitric acid addition

Ì

Cell performance is highly dependent on concentration and temperature as well as cell design


Single cell performance @ 25oC, 42째C, 56oC Cell size 30mm 250

56oC

Power Density (mW/cm2)

200

42oC

150

25oC 100

50

0 0

100

200

300

400

500

600

700

Current Density (mA/cm2)

Higher temperature operation sustains current density up to 500 mA/cm2; produces peak power density of about 190 mW/cm2


Effect of catholyte concentration on single cell power density Cell size 30mm

ĂŒ

The increase in power due to temperature or increasing concentration of nitric acid in the catholyte is accompanied by an increase in nitric crossover in certain fuel cell operating regimes


43mm single cell performance (Methanol-Nitric) @25oC Polarization Curves for 43mm- Single Fuel Cells (std. methanol-nitric)

43mmx43mm

Cell ID: 20090327_5A_BNK_FC_CM086_KS 120.0

1.000 0.900

100.0

0.800 0.700

Volts

0.600 60.0

0.500 0.400

30mmx30mm

Power (W)

80.0

40.0

0.300 0.200

20.0

0.100 0.000 0

50

100

150

200

250

300

0.0 350

Current Density (mA/cm2) Vout (VDC)

ĂŒ

Probe A (V)

Probe C (V)

Vsep

Power Density (mW/cm2)

Anolyte: 2M CH3OH + 4 M H2SO4 Catholyte:1.75 M HNO3 + 8 M H2SO4

Electrode size is scalable to preferred form factors


Single cell performance (43mm) Formic acid anolyte (6M, Closed loop) 20081119_2C_EXP_FC_LE005_KS Stability 100 90

0.8

80

Voltage(V)

0.7

70

Vc, Cathode Voltage Vfc, Fuel Cell Voltage

0.6

60

Va, Anode Voltage Vsep, Separation Voltage

0.5

50

Power Density, mW/cm2

0.4

40

0.3

30

0.2

20

0.1

10

20081027_1B_EXP_FC_JK012_DRW Stability 1

0

100

0 0.9 40

60

80

100

120

Time (min) Current used: 3 Amp Anolyte: 6M HCOOH/4M H2SO4 (closed loop, volume 50 ml, flow rate 4 ml/min) Catholyte: 1.75 M HNO3/8M H2SO4 (open loop, flow rate 4ml/min)

90

Vfc, Fuel Cell Voltage

0.8

80

Va, Anode Voltage Vsep, Separation Voltage

0.7

70

Power Density, mW/cm2

Voltage(V)

20

Vc, Cathode Voltage

0.6

60

0.5

50

0.4

40

0.3

30

0.2

20

0.1

10

0

0 0

50

100

150

200

Time (min)

250

300

350

Power Density (m W /cm 2)

0.9

Power Density (mW/cm2)

1


Neah’s technology demonstrator Ì Ì Ì Ì Ì

Demonstrate basic balance of plant closed-loop operation for 1 hour, multiple runs Cell array spread out for interchangeable cells Ejecting and swappable cartridge, NOx capture/scrubber Electronics for start-up, shut down, electro clean, pressure and temp. monitor Serviceable PCB, stack, refillable cartridge

Electronics

Removable Cell carriers cartridge Pumps

Ejection handle

Anolyte tank Catholyte tank

Enclosure Cartridge/Stack manifold

Scrubbed NOx (<25ppm)


Performance of 10 cell stack on demonstrator (10 cells)

Catholyte: 1.75 M HNO3/8M H2SO4

14

Voltage (V)

2M CH3OH/0.5M HCOOH/4M H2SO4

7

12

6

10

5

8

4

6

3

4

2

2

1

0

0 0

10

20

30

40

50

60

Amps/ Power (W)

Anolyte:

70

Time (min) Stack VDC

Amps

Stack Power

The power decline stems partly from close loop operation with no regeneration and the noise can be corrected by electronics.


Performance of Neahâ&#x20AC;&#x2122;s demonstrator supporting BoP + test load 14

12

Stack V Stack Amps

10

Amps, Volts, Watts

Load Amps BOP Amps Stack W Load W

8

BOP W Converter output +12V 6

4

2

0 0

2

4

6

8

10

12

14

16

18

20

Time (min) Anolyte:

2M CH3OH/0.5M HCOOH/4M H2SO4

Catholyte: 1.75 M HNO3/8M H2SO4

Net +ve power output follows load power, and it can be increased with additional cells/stacks


Stack volume reduction Ì Ì

Stack size reduction by embedding fluidic delivery Stack volume minimal (90% volume decrease from Prototype 1)

• Prototype 2 integrated stack volume ~ 441cm3 • Prototype 1 stack volume ~4,737cm3

Ì

Further stack reduction through thinning of micro fluidic layers

4-cell stack with thin fluidic layers 10-cell stack with embedded fluidic layers


Performance of reduced volume 10-cell stack @ Rm. temp Anolyte continuously refreshed, catholyte recirculated 12

10

Amps Volts Stack Power

Amps, Volts, Watts

8

6

4

2

0 0:00:00

0:05:46

0:11:31

0:17:17

0:23:02

0:28:48

Time (min)

0:34:34

0:40:19

0:46:05


Further Improvements Ì

Cell

Ì

Stack

• • • • • •

Catalysts Construction Chemistry Integration ƒ

Stack and Balance of Plant (BOP) components into monolithic module

Bonding ƒ

Entire stack of cells to eliminate compression hardware

Electrical ƒ

Connections and resistances

Ì

Electronics

Ì

Fluidics

Ì

System Integration

• • • • • • •

Minimize power draw, and losses Miniaturized MEMS, sensors, PCB Integrate sensor layer within stack module Peak power capability & efficient load sharing Cells and Stacks Miniaturize/multi-functionalize components higher volumetric packaging efficiency


Summary Ì Ì Ì

Ì

Temperature and chemistry optimization may provide up to a 40% increase in power performance Methanol and formic fuels, along with liquid and air and oxygen oxidants may be used A porous silicon based all liquid fuel cell system has been developed for air-free applications (>1 hr run time, BoP support, net power generation, swappable cartridges) The stack volume has been decreased by 90% compared to single cell carrier design and size and performance continues to improve for applications


Acknowledgement

Ì

The US Office of Naval Research

• Phase-II Contract # N00014-08-C-0474


Recognitions

NIST/ATP $2M Award Sept. 2003

“Startup of the Year” Seattle Alliance of Angels May 2004

Red Herring Top 100 Innovators Dec. 2004

Leroy Ohlsen Top 100 Young Innovators Sept. 2004

Venture All-Stars Top 25 Company June 2005

ONR Award July 2007 & Sept 2008 23

The Neah Fuel Cell  
The Neah Fuel Cell  

Neah's revolutionary fuel cell.

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