Brandon Johnson University Of California, Irvine Department of Electrical Engineering and Computer Science Mentor: Dr. Marc Madou University Of California, Irvine Chancellor's Professor Department of Mechanical and Aerospace Engineering Analyzing the Properties of IrOx Derived Electrochemical Sensors

Electrochemistry Background How 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? Glass pH electrodes have their short commings Glass pH electrodes have their short commings Extremely fragile Extremely fragile Relatively slow response times Relatively slow response times Short lifetime Short lifetime Cannot be used in certain media Cannot be used in certain media Alkaline Alkaline HF HF Organic Solutions Organic Solutions

Science Looks Into Metal Oxides Various Metal Oxides tested Various Metal Oxides tested Sb 2 O 3 Sb 2 O 3 Widely used for acid based titrations or solutions containing HF. However potential drift makes this unsuitable for pH measurements. Widely used for acid based titrations or solutions containing HF. However potential drift makes this unsuitable for pH measurements. Bi 2 O 3 Bi 2 O 3 Used in pH measurements for KOH Used in pH measurements for KOH PtO 2, IrO 2, RuO 2, OsO 2, TaO 5, RhO 2, TiO 2, SnO 2 PtO 2, IrO 2, RuO 2, OsO 2, TaO 5, RhO 2, TiO 2, SnO 2 IrO 2 held the most promise IrO 2 held 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 IrOx Electrochemical growth Electrochemical growth Electrodeposition Electrodeposition Sputtered Coating Sputtered Coating Thermal method Thermal method Printing Method Printing Method Lithium Carbonate (Li 2 CO 3 ) melt bath Lithium Carbonate (Li 2 CO 3 ) melt bath

Initial Claims Regarding these IrOx Sensors Extremely consistent E o regardless of storage medium Extremely consistent E o regardless of storage medium

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

Initial Claims Regarding these IrOx Sensors Consistent and stable readings across a variety of pH’s Consistent and stable readings across a variety of pH’s

Initial Claims Regarding these IrOx Sensors

Additionally these sensors claimed to be stable in 4M HCL or a 5M H 2 SO 4 solution Additionally these sensors claimed to be stable in 4M HCL or a 5M H 2 SO 4 solution Claimed to have excellent mechanical stability Claimed to have excellent mechanical stability

The Problem These results were not corroborated in industry for some time. These results were not corroborated in industry for some time.

Initial Results Results in a buffer of pH 8

Initial Results Results in a buffer of pH 3

Initial Results Analysis of Nernstian Slope

pHWorkingProbe-B4Probe-B5Probe-B6Probe-B7Probe-K1Probe-K2Probe-K slope Initial Results Analysis of Nernstian Slope

So far the slopes look good but the E o has an almost 200mV deviation between the probes So far the slopes look good but the E o has an almost 200mV deviation between the probes The response times are extremely slow The response times are extremely slow Initial Results

Off to the SEM

Significance of the BSE Results The IrOx was not uniform The 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 the pH buffer solution? Was there some sort of residue from being in the pH buffer solution?

The Answer The required break-in period The required break-in period Conversion of the Li 8 IrO 6 to an unknown structure Conversion of the Li 8 IrO 6 to an unknown structure Additionally hydration plays a major role in the ability of the IrOx sensors to respond rapidly and correctly Additionally hydration plays a major role in the ability of the IrOx sensors to respond rapidly 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.

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

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

Results Extrapolated slopes of 4 hydrated probes, post break-in

Results pHProbe-K1Probe-K5Probe-K8Probe-K slope

Results Probe stability and response results across a variety of pH buffers

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

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

Results Response time for a standard glass bulb working electrode

Results Results from a test in H 2 S0 4

Results An interesting result regarding mechanical stability

Significance Consistencies with original publications Consistencies with original publications Response times consistent with original publications Response times consistent with original publications Stability in a wide range of pH buffers also confirmed Stability in a wide range of pH buffers also confirmed Discrepancies with original publications Discrepancies with original publications Break-in period Break-in period Necessity of hydration Necessity of hydration Possibly the stability in a solution Possibly the stability in a H 2 S0 4 solution Consistency of the E Consistency of the E o

Acknowledgements Mentor: Dr. Marc Madou Mentor: Dr. Marc Madou Lab Team: Kelvin Cheung, Jim Zoval, Horacio Kido, Chunlie (Peggy) Wang, Rabih Zaouk, Benjamin Park, Francesc Jornet, and Kuosheng Ma Lab Team: Kelvin Cheung, Jim Zoval, Horacio Kido, Chunlie (Peggy) Wang, Rabih Zaouk, Benjamin Park, Francesc Jornet, and Kuosheng Ma IM-SURE: Said Shokair, Jerry McMillan, Goran Matijasevic IM-SURE: Said Shokair, Jerry McMillan, Goran Matijasevic National Science Foundation (NSF) National Science Foundation (NSF)