Development of Novel NOx Sensors and System Integration with Alumina Heater Elements

Size: px

Start display at page:

Download "Development of Novel NOx Sensors and System Integration with Alumina Heater Elements"

Thomasine Harrison
6 years ago
Views:

1 Development of Novel NOx Sensors and System Integration with Alumina Heater Elements UC Riverside PEMS 2016 International Conference & Workshop March 17, 2016 F. Bell, M. Boettcher, J. Chee, J. Fitzpatrick, S. Harding, B. Henderson, D. Lippoth, M. Phee, L. Sorensen, V. Wang, and L.Y. Woo R. F. Novak and J. H. Visser (Ford Motor Company)

NOx sensors currently in vehicles and our novel method both related to O 2 sensor technology In vehicles now amperometric operation (dc current) of solidstate electrochemical cell Multiple cells to

2 NOx sensors currently in vehicles and our novel method both related to O 2 sensor technology In vehicles now amperometric operation (dc current) of solidstate electrochemical cell Multiple cells to pump out O 2 and measure remaining NOx Difficulty detecting sub 5 ppm and poor durability of complex probes h$ps:// 14K0U Our method novel single-cell impedancemetric operation - Two electrodes with specific oxygen catalyst properties covered with porous yttria-stabilized zirconia (YSZ) O 2- conducting ceramic electrolyte placed directly in gas - Applied oscillating signal with resulting wave distortion analyzed - Potential for lower cost and better performance System integration with alumina heater elements 2

3 Impedancemetric sensing: Yttria-stabilized zirconia (YSZ) electrolyte conducts O 2- >600 C Requires at least one sensing electrode: symmetric or asymmetric cells with design flexibility 1 O 2-2 O + 2 2e O 2 NO 2 + 2e NO + O 2 Electrode 1 Electrolyte: Electrode 2 θ Ohm s Law: V(t)=I(t) Z(ω) time Output Current I(t) Applied Voltage V(t) Im(Z) θ = tan 1 Re(Z) Phase angle Complex impedance: AC response to small amplitude signals over a range of frequencies Non equilibrium multiple reactions Z(ω) = Re(Z) +jim(z) Z = (Re(Z)) 2 + (Im(Z)) 2 Magnitude Im(Z) Z'' Z θ Z' Re(Z) 3

For operation, choose phase angle (θ) at 5-50 Hz and 100 mv excitation 15 10.5% O 2 ~2% H2O, 625 C ~2% H2O, 625 C -Im(Z) [k!] 10 18.9% O 2 10.

4 For operation, choose phase angle (θ) at 5-50 Hz and 100 mv excitation % O 2 ~2% H2O, 625 C ~2% H2O, 625 C -Im(Z) [k!] % O % O +100 ppm NO Z '' θ'' θ' Re(Z) [k!] Z ' Less than ~1 khz: Impedance (phase angle, θ, and magnitude, Z ) decrease with increasing NOx and O 2 Oxygen methods for extraction Phase angle (θ) better stability and sensitivity than Z 4

Development of lower cost electronics led to surprising discovery about sensor response Triangle

For portable low-cost digital electronics, explored triangle wave form and zero-crossing

5 Development of lower cost electronics led to surprising discovery about sensor response Triangle source Source/Output Sensor output Precision laboratory equipment (Solartron 1260) costs ~ $50k For portable low-cost digital electronics, explored triangle wave form and zero-crossing detection Complex response to triangle wave source showed peak relatively unchanged no phase shift! Digital voltage-current time differential method using complex changes in asymmetric wave form NOx and O 2 concentration alter different portions of wave in time basis for extracting oxygen time 5

6 Sensing relies on electrochemical reaction rates at the electrode/electrolyte interfaces electrolyte electrode O O 2 + 2e O 2 NO 2 + 2e NO + O 2 Impedance reaction rates with different frequency dependencies NOx and O 2 influence < 1 khz Parallel contributions from both Resolve ppm NOx changes in large 2-21% O 2 background by limiting O 2 reaction rate with porous YSZ electrolyte Low sensitivity High sensitivity Adsorption Adsorption Diffusion Electrode YSZ O -2 e - Charge-transfer Minimal NOx response when electrode surface dominates YSZ O -2 e - Diffusion Charge-transfer Electrode Larger NOx response: controlling microstructure and composition is key 6

7 System integration of NOx sensor designs with Al 2 O 3 heater for more deployable prototypes More advanced designs suitable for single higher temperature cofiring step with Al 2 O 3 for easier processing and improved robustness Bonding of porous YSZ electrolyte to Al 2 O 3 Incorporating more desirable processing techniques such as screen-printed electrodes Packaging and electrical connections to heater and sensor 7

Continued evolution of designs starting with hand-assembled single-cell lab prototypes Top view Au wire YSZ Pt Alumina Cross-section Phase angle, 10 Hz, 100 mv (degrees) Al 2 O 3 substrates and Pt

8 Continued evolution of designs starting with hand-assembled single-cell lab prototypes Top view Au wire YSZ Pt Alumina Cross-section Phase angle, 10 Hz, 100 mv (degrees) Al 2 O 3 substrates and Pt leads fired ~ 1500 C Followed by separate lower temperature (1000 C) post-firing step for Au wire and porous YSZ Sensitivity < 5 ppm, response < 5 sec for 10 ppm Stable reproducible signal > 1000 hours and durability > 3800 hours Low cross-sensitivity to water % O ppm NO 5 +0 ppm NO 650 C Time (Min) 8

5 in 1450 C as target minimum for cofiring with Al2O3 Tape cast YSZ thickness (before firing) ~10 mils: laminated 2 layers

9 More advanced designs: Au ribbon constrained by YSZ layers suitable for cofiring with Al2O3 1.4 in 0.26 in Polish to expose contact pads at ends for electrical leads 0.5 in 1450 C as target minimum for cofiring with Al2O3 Tape cast YSZ thickness (before firing) ~10 mils: laminated 2 layers above and 2 layers below Au ribbons Au ribbons: ~11 mils width x 5 mils thickness with 25 mil spacing between Fugitive material added to Au ribbon channels to account for larger shrinkage of ceramic 9

5-40 -39.5-39 -38.5 725 C, 5 Hz, 100 mv 10.

10 Previously, two different porous YSZ studied for constraining Au at 1450 C (no Al 2 O 3 heater) Adding 22 vol% carbon black as pore former; ~23% porosity Calcined YSZ at 1300 C to reduce sintering kinetics; ~16% porosity Phase angle (degrees) C, 5 Hz, 100 mv 10.5% O ppm NO Time (sec) 5µm -42 5µm + 10 ppm NO Phase angle (degrees) C, 5 Hz, 100 mv 10.5% O ppm NO ppm NO Time (sec) 10

11 Investigate cofiring two different porous YSZ with Al 2 O 3 at 1450 C Top view Carbon black Calcined YSZ Side view Both types of porous YSZ bonded to Al 2 O 3 Densification of porous YSZ near interface with Al 2 O 3 More porosity (indicated by uptake of red dye) in calcined YSZ better sensor performance 11

Evidence of interfacial structure and strong bonding in calcined YSZ with Al 2 O 3 Calcined YSZ Fine-grain structure in calcined YSZ near interface with Al 2 O 3 96% Al 2 O 3 20µm Thermal cycling and

12 Evidence of interfacial structure and strong bonding in calcined YSZ with Al 2 O 3 Calcined YSZ Fine-grain structure in calcined YSZ near interface with Al 2 O 3 96% Al 2 O 3 20µm Thermal cycling and autoclave testing indicated strong durable bonding at YSZ/Al 2 O 3 interface Due to strong bonding and better porosity than carbon black, used calcined YSZ for developing working sensors with Au electrodes and Pt leads integrated with Al 2 O 3 heater elements 12

13 1450 C cofiring of Au electrode and Pt lead showed poor electrical continuity Novel material interconnect developed to allow electrical contact between Au electrode and Pt lead 13

14 Verified performance of sensor designs using novel material interconnect solution -Im(Z) ohms # POC-6 H14B-23, Day sccm; ~590degC (8.98V/1.02A) Au ribbon/ysz/al 2 O % O2 +100ppm NO % O ppm NO 10.5% O 2 POC-6-H14-23, Day 1 5% O 2 +10ppm NO 5% O 2 15% O 2 5 Hz 20Hz ppm NO 0.5 ~590 C Re(Z) ohms # % O ppm NO ~590 C Time (sec) 14

15 Replace Au ribbon electrode with Au paste for all screen-printed sensor prototype Au ribbon/ysz/al 2 O 3 Au paste/ysz/al 2 O % O ppm NO 10.5% O 2 POC-6-H14-23, Day 1 5% O 2 +10ppm NO +10ppm NO 5% O 2 15% O 2 5 Hz 20Hz % O ppm NO ~590 C Time (sec) % O ppm NO 10.5% O 2 IS-1-32, Day 1 +10ppm NO +10ppm NO 5% O 2 15% O 2 5 Hz 20Hz 15% O ppm NO ~590 C Time (sec) 15

16 Development of packaging for operating NOx sensor prototypes with Al 2 O 3 heaters Concept design to understand role of: Venturi tip Crushable gas seal Electrical connection 16

17 Maintaining sensor performance as designs evolve towards more deployable prototype Phase angle 5 Hz, 100 mv (deg) 3 Cofired constrained Au ribbon/porous YSZ % O FSB2, Day ppm ppm NO 725 C Furnace heated Time (sec) 3 Cofired Au ribbon/ysz/al 2 O 3 POC-6-H14-23, Day % O ppm ppm NO -46 ~590 C Heated element Time (sec) 3 Cofired Au paste/ysz/al 2 O 3 IS-1-32, Day % O ppm ppm NO ~590 C Heated element Time (sec) 17

18 Next steps Improving shrinkage match to reduce bowing Optimizing novel interconnect material solution Re-evaluating aging/drift and sensitivity to NO 2, H 2 O, and NH 3 in more advanced designs to compare with previous data from earlier designs Modifying electronics for compatibility with more advanced designs Continuing to improve Al 2 O 3 heater operation and develop packaging 18

19 Summary Novel single-cell impedancemetric sensor Wave distortion from applied oscillating signal digital voltage-current time differential Potential for lower cost and better performance System integration of NOx sensor designs with Al 2 O 3 heater for more deployable prototypes Constrained gold electrodes suitable for cofiring with Al 2 O 3 for easier processing and improved robustness Good bonding of calcined YSZ to Al 2 O 3 Novel material interconnect solution for Au and Pt All screen-printed design and packaging development Questions? Thank you for you attention! lw@emisense.com 19

Surface Coatings on High-Voltage Electrodes of Electrostatic Particulate Matter (PM) Sensors

Surface Coatings on High-Voltage Electrodes of Electrostatic Particulate Matter (PM) Sensors UC Riverside PEMS 2017 International Conference & Workshop March 30, 2017 M. Boettcher, J. Fitzpatrick, B. Henderson,