Brandon JohnsonUniversity Of California, Irvine

Department of Electrical Engineering and Computer Science

Mentor: Dr. Marc MadouUniversity Of California, Irvine

Chancellor's Professor Department of Mechanical and Aerospace Engineering

Analyzing the Properties of IrOx Analyzing the Properties of IrOx Derived Electrochemical SensorsDerived Electrochemical Sensors

Electrochemistry BackgroundElectrochemistry BackgroundHow does electrochemical sensing work?

Snoswell, David Robert Evan. The Influence of Surface Heterogeneity and Solution Composition on the Colloid Stability of SiO2 and TiO2 Dispersions, Australian Digital Thesis Program, 2003.

Why Are We Even Interested?Why Are We Even Interested? Glass pH electrodes have their short commingsGlass pH electrodes have their short commings

Extremely fragileExtremely fragileRelatively slow response timesRelatively slow response timesShort lifetimeShort lifetimeCannot be used in certain mediaCannot be used in certain media

AlkalineAlkalineHFHFOrganic SolutionsOrganic Solutions

Science Looks Into Metal OxidesScience Looks Into Metal Oxides

Various Metal Oxides testedVarious Metal Oxides tested SbSb22OO33

Widely used for acid based titrations or solutions containing Widely used for acid based titrations or solutions containing HF. However potential drift makes this unsuitable for pH HF. However potential drift makes this unsuitable for pH measurements.measurements.

BiBi22OO33

Used in pH measurements for KOHUsed in pH measurements for KOH PtOPtO22, IrO, IrO22, RuO, RuO22, OsO, OsO22, TaO, TaO55, RhO, RhO22, TiO, TiO22, SnO, SnO22

IrOIrO2 2 held the most promiseheld the most promise

Sheng Yao, Min Wang, and Marc Madou. A pH Electrode Based on Melt-Oxidized Iridium Oxide, Journal of The Electrochemical Society, 148 (4) H29-H36 (2001)

Methods of Creating IrOxMethods of Creating IrOxElectrochemical growthElectrochemical growthElectrodepositionElectrodepositionSputtered CoatingSputtered CoatingThermal methodThermal methodPrinting MethodPrinting MethodLithium Carbonate (LiLithium Carbonate (Li22COCO33) melt bath) melt bath

Initial Claims Regarding these IrOx SensorsInitial Claims Regarding these IrOx Sensors

Extremely consistent EExtremely consistent Eoo regardless of storage medium regardless of storage medium

Initial Claims Regarding these IrOx SensorsInitial Claims Regarding these IrOx Sensors Super fast response timesSuper fast response times

Initial Claims Regarding these IrOx SensorsInitial Claims Regarding these IrOx Sensors Consistent and stable readings across a variety Consistent and stable readings across a variety

of pH’sof pH’s

Initial Claims Regarding these IrOx SensorsInitial Claims Regarding these IrOx Sensors

Initial Claims Regarding these IrOx SensorsInitial Claims Regarding these IrOx Sensors

Additionally these sensors claimed to be stable Additionally these sensors claimed to be stable in 4M HCL or a 5M Hin 4M HCL or a 5M H22SOSO4 4 solutionsolution

Claimed to have excellent mechanical stabilityClaimed to have excellent mechanical stability

The ProblemThe ProblemThese results were not corroborated in These results were not corroborated in

industry for some time.industry for some time.

Initial ResultsInitial Results

1.50E-01

2.00E-01

2.50E-01

3.00E-01

3.50E-01

0 200 400 600 800 1000

Probe 2Probe 4Probe 5Probe 6Probe 7

Results in a buffer of pH 8

5.20E-01

5.40E-01

5.60E-01

5.80E-01

6.00E-01

6.20E-01

6.40E-01

6.60E-01

6.80E-01

0 500 1000 1500 2000 2500

Probe 2Probe 4Probe 5Probe 6Probe 7Working

Initial ResultsInitial ResultsResults in a buffer of pH 3

-400

-200

0

200

400

600

800

1000

0 2 4 6 8 10 12 14

WorkingProbe-B4Probe-B5Probe-B6Probe-B7Probe-K1Probe-K2Probe-K3

Initial ResultsInitial ResultsAnalysis of Nernstian Slope

pH Working Probe-B4 Probe-B5 Probe-B6 Probe-B7 Probe-K1 Probe-K2 Probe-K3

0   720.5 766.417 806.083 833.583 656.944 737.996 753.7

2 354 600 648 686 720 553 620 633

3 295 536 579 616 656 494 544 556

6.01 116 380 413 446 480 379 353 370

8.12 -15 227 279 317 360 273 234 229

10.04   130 188 219 271 165 137 146

11.06           110 89.5 86.8

12.08 -239         57.5 30.8 34.9

slope 60.0417 60.25 59.2083 60.0417 56.7917 51.9722 58.9778 60.35

Initial ResultsInitial Results

Analysis of Nernstian Slope

So far the slopes look good but the ESo far the slopes look good but the Eo o has has an almost 200mV deviation between the an almost 200mV deviation between the probesprobes

The response times are extremely slowThe response times are extremely slow

Initial ResultsInitial Results

Off to the SEMOff to the SEM

Off to the SEMOff to the SEM

Off to the SEMOff to the SEM

Off to the SEMOff to the SEM

Off to the SEMOff to the SEM

Significance of the BSE ResultsSignificance of the BSE ResultsThe IrOx was not uniformThe IrOx was not uniform

Was there a polymer coating?Was there a polymer coating?Was there damage done to the probe?Was there damage done to the probe?Was there some sort of residue from being in Was there some sort of residue from being in

the pH buffer solution?the pH buffer solution?

The AnswerThe AnswerThe required break-in periodThe required break-in periodConversion of the LiConversion of the Li88IrOIrO66 to an unknown to an unknown

structurestructureAdditionally hydration plays a major role in Additionally hydration plays a major role in

the ability of the IrOx sensors to respond the ability of the IrOx sensors to respond rapidly and correctlyrapidly and correctly

Chrisanti, Santi. A pH Electrode Based on Melt-Oxidized Iridium Oxide, A Thesis Presented in Partial Fulfillment of the Requirement for the Degree Master of Science in the Graduate School of The Ohio State University, 2003.

ResultsResults

5.50E-01

5.60E-01

5.70E-01

5.80E-01

5.90E-01

6.00E-01

6.10E-01

0 200 400 600 800 1000 1200 1400 1600

Example response time of a non-hydrated probe after the initial break-in period

ResultsResults

4.00E-01

4.20E-01

4.40E-01

4.60E-01

4.80E-01

5.00E-01

5.20E-01

5.40E-01

0 20 40 60 80 100 120

Example response time of a hydrated probe after the initial break-in period

ResultsResults

-100

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12 14

Probe-K1 Probe-K5 Probe-K8 Probe-K10

Extrapolated slopes of 4 hydrated probes, post break-in

ResultsResults

pH Probe-K1 Probe-K5 Probe-K8 Probe-K10

0 732.667 650.5 643.833 718.7778

2 609 534 518 590

3 550 478 458 512

6.01 363 298 263 340

8.12 225 180 136 216

10.04 111 83 10 94

11.06 50 34 -50 35

12.08 -18 -43 -116 -34

slope 61.8333 58.25 62.9167 64.38889

ResultsResults

-2.00E-01

-1.00E-01

0.00E+00

1.00E-01

2.00E-01

3.00E-01

4.00E-01

5.00E-01

6.00E-01

7.00E-01

0 200 400 600 800 1000 1200 1400 1600

Probe 1 Probe5 Probe8 Probe10

Probe stability and response results across a variety of pH buffers

ResultsResults

3.50E-01

4.00E-01

4.50E-01

5.00E-01

5.50E-01

6.00E-01

6.50E-01

150 200 250 300 350 400 450

Response time for a pH jump from pH 2 to pH 5.5

ResultsResults

4.00E-01

4.20E-01

4.40E-01

4.60E-01

4.80E-01

5.00E-01

5.20E-01

5.40E-01

55 60 65 70 75

Response time for a pH jump from pH 2 to pH 3.5

ResultsResults

3.20E-01

3.25E-01

3.30E-01

3.35E-01

3.40E-01

3.45E-01

3.50E-01

3.55E-01

3.60E-01

3.65E-01

0 50 100 150 200 250 300

Response time for a standard glass bulb working electrode

ResultsResults

5.75E-01

5.80E-01

5.85E-01

5.90E-01

5.95E-01

6.00E-01

6.05E-01

6.10E-01

6.15E-01

6.20E-01

6.25E-01

0 200 400 600 800 1000 1200 1400 1600

Results from a test in H2S04

ResultsResults

An interesting result regarding mechanical stability

SignificanceSignificanceConsistencies with original publicationsConsistencies with original publications

Response times consistent with original publicationsResponse times consistent with original publications Stability in a wide range of pH buffers also confirmedStability in a wide range of pH buffers also confirmed

Discrepancies with original publicationsDiscrepancies with original publications Break-in period Break-in period Necessity of hydrationNecessity of hydration Possibly the stability in a Possibly the stability in a H2S04 solutionsolution Consistency of the EConsistency of the Eo

AcknowledgementsAcknowledgements Mentor: Dr. Marc MadouMentor: Dr. Marc Madou Lab Team: Kelvin Cheung, Jim Zoval, Horacio Lab Team: Kelvin Cheung, Jim Zoval, Horacio

Kido, Chunlie (Peggy) Wang, Rabih Zaouk, Kido, Chunlie (Peggy) Wang, Rabih Zaouk, Benjamin Park, Francesc Jornet, and Kuosheng Benjamin Park, Francesc Jornet, and Kuosheng MaMa

IM-SURE: Said Shokair, Jerry McMillan, Goran IM-SURE: Said Shokair, Jerry McMillan, Goran MatijasevicMatijasevic

National Science Foundation (NSF)National Science Foundation (NSF)