4th International Conference on Hydrogen Safety (ICHS) September 12-14, 2011 1 Low Energy Hydrogen Sensor Linke, S., Dallmer, M., Werner R. and Moritz,

1

4th International Conference on Hydrogen Safety (ICHS)

September 12-14, 2011

Low Energy Hydrogen Sensor

Linke, S., Dallmer, M., Werner R. and Moritz, W.Humboldt University of Berlin, Brook-Taylor-Str.2, 12489 Berlin, Germany;

email: [email protected]

Sensor structure

Hydrogenresponse

Thermalreactivation

Firedetection

LFLExplosion

alarm

2



Sensor structure

Si3N4

SiO2

Si

Palladium

•Disadvantages of available

hydrogen sensors:•energy consumption too high for battery powered systems due to elevated working temperature

•price to high for mass products

•poor selectivity

3



Electrochemical mechanism ((different to Lundström type))

Palladium

Si LaF3

CV-measurement

4



Response of the Pd/LaF3/Si3N4/SiO2/Si field effect structure (solid line and left scale) to different concentrations of hydrogen (doted line and right scale) in synthetic air;

room temperature; measurement 1 hour after preparation of the Pd layer

5



0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-20

0

20

40

60

80

100

120

140G

ate

volta

ge s

hift

(m

V)

Time (s)

0

20

40

60

80

100

120

140

160

180

200

220

240

Hyd

roge

n co

ncen

trat

ion

(ppm

)

6 days after preparation

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Heating and temperature measurement

1 - Pt; 2 - LaF3; 3 - SiO2/Si3N4; 4 - n-Si; 5 - ohmic contact

No method for fast surface temperature measurement

4-point measurementresistance of Pt

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C o m p ute r

R = 1I

TTL

C o ntro l vo lta g e0-5 V

Lo w vo lta g e im p u lse Hig h vo lta g e20 -1500 V

Diffe re ntia lp ro b e s

IEEE 488

Tra nsfo rm e d h ig vo lta g e im p u lse

Trig g e rsig na l

IR-LEDsin o ut

RM e ss

C o ntro l vo lta g e

vo lta g e o ut

+G a s 1

G a s 2

G a s e xha ust

Re la isTTL

sig na l in

Sa m p le ho ld e r

RS23 2

O p tic s

p ho to c urre ntm e a sure m e nt

Po we r p ulse so urc e

Surfa c ete m p e ra ture

m e a sure m e nt

Se nsitivitym e a sure m e nt

8



Calculations of temperature distribution

100ns 1000W100WS

LaF3

240 nm

SiO2/Si3N4

80nm

1 s10 W10Ws

10 s100W1mWs

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Constant surface temperature

0 200 400 600 800 1000300

400

500

600

700

310 nsT<5K

tem

pera

tur/

K

t/ns

Parameters of the electrical heating pulse used in Fig. aboveMax. current 8,4ACur. dens. 2,8*107 Acm-2

Max. voltage 293 VMax. power 2365 WTotal energy 1,82*10-3 J((average 2x10-8 W))

TSi=0,025 K

500 activations simulating 2 years

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Micro hotplate structure

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Temperature distributionfor different impulse duration

Average power consumption 2x10-6 WFast decay to room temperature

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Hydrogen signal in air after thermal reactivation

room temperature

Low concentration range

136 mV/decade

Limit of detection500 ppb

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A Fire Experiment in a Wooden House..........T- Amamoto et al., Sensors and Actuators, B1 (1990) 226-230

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800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30

35

40

45

ventilation on

Start Heater

TF 2

sig

na

l/mV

t/s

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

hydrogen-sensor90 sec earlier

CO-conc

smoke-sensor

-10

0

10

20

30

40

50

60

Early state of Fire (smoldering)TF 2 wood on electrical heater

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September 12-14, 2011 High concentration range

LFL 4% (40 000 ppm)alarm level 1,6%

Response time t90 (@8000 ppm)= 4 s

150 mV/dec

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Stress test simulating330 days of activations and mesurements

Day 2, 50, 150 and 300

all 330 measurements

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Mechanism

Oxygen sensor

O2 + A* O2 (A*) (1)

O2 (A*) + H2O + e- HO2 (A*) + OH- (2)

OH- + (F*) OH-(F*) (3)Additional hydrogen action

O2 (A*) + H2 H2O (A*) (4)

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Conclusions

- room temperature hydrogen sensor in ppm range and for high concentration

- thermal reactivation is possible

- Low energy consumption for heating impuls

- early fire detection

- alarm at lower explosion level

- Battery power application for long time

- Combination with energy harvesting technology possible

Documents

4th International Conference on Hydrogen Safety (ICHS) September 12-14, 2011 1 Low Energy Hydrogen Sensor Linke, S., Dallmer, M., Werner R. and Moritz,