Mixed Potential Electrochemical Sensors – Ceramic Substrate and Electrolyte Effects on Sensor Response to Methane and Simulated Natural Gas
Authors: Halley Sleight , Ramaiyan Kannan , Agi Kamil , Garzon Fernando H. , Tsui Lok-kun 
Published: July 2022

The US Environmental Protection Agency estimates emissions from US natural gas drilling and processing amounted to 197 million metric tons of CO2 equivalent in 2019.1 Research by Marchese et al. suggests that CH4 emissions could be up to three times higher.2 Current natural gas emissions detection methods consist mainly of active optical monitoring, typically with long path IR sensors.3 These monitoring methods capable of ppb level accuracy are expensive, fragile, and require accurately calibrated mirrors. Mixed potential electrochemical sensors (MPES) are robust, low-cost, and selective sensors, making them appropriate option for methane emission monitoring.4 Previously we have reported on a four electrode MPES with 3 mol% YSZ electrolyte fabricated with direct write 3D printing5, here we investigate substrate and electrode material effects on the sensor response.
The response of a four electrode La0.87Sr0.13CrO3, Indium Tin Oxide (In2O3 90 wt%, SnO2 10 wt%), Au, Pt mixed potential electrochemical sensor to methane and simulated natural gas at operating temperatures of 450 – 600 °C was studied. Sensors were fabricated on substrates of yttria stabilized zirconia, ceria stabilized zirconia, and magnesia stabilized zirconia manufactured by direct write extrusion 3D printing of aqueous pastes. These materials are selected to maximize the mixed potential difference by better isolation of the sensing electrodes. Data is presented with a solid electrolyte of 3 mol % yttria stabilized zirconia, and various other solid ceramic electrolytes will be studied. The effect of sensor response with respect to the ionic conductivity of substrate material is studied. The sensor limit of detection for CH4, natural gas, CH4/NH3, and CH4/H2 mixes will be reported. We will also train artificial neural networks to quantify the concentration of CH4 and other subcomponents given a subset of signals taken from the sensors operated at different temperatures.
Acknowledgements
This project was supported by US Department of Energy Office of Fossil Energy and Carbon Management through award DE-FE0031864.
References
(1) US EPA, O. Estimates of Methane Emissions by Segment in the United States https://www.epa.gov/natural-gas-star-program/estimates-methane-emissions-segment-united-states (accessed 2021 -12 -13).
(2) Marchese, A. J.; Vaughn, T. L.; Zimmerle, D. J.; Martinez, D. M.; Williams, L. L.; Robinson, A. L.; Mitchell, A. L.; Subramanian, R.; Tkacik, D. S.; Roscioli, J. R.; Herndon, S. C. Methane Emissions from United States Natural Gas Gathering and Processing. Environ. Sci. Technol.
2015, 49 (17), 10718–10727. https://doi.org/10.1021/acs.est.5b02275.
(3) Aldhafeeri, T.; Tran, M.-K.; Vrolyk, R.; Pope, M.; Fowler, M. A Review of Methane Gas Detection Sensors: Recent Developments and Future Perspectives. Inventions
2020, 5 (3), 28. https://doi.org/10.3390/inventions5030028.
(4) Garzon, F. H.; Mukundan, R.; Brosha, E. L. Solid-State Mixed Potential Gas Sensors: Theory, Experiments and Challenges. Solid State Ion.
2000, 136, 633–638.
(5) Halley, S.; Tsui, L.; Garzon, F. Combined Mixed Potential Electrochemical Sensors and Artificial Neural Networks for the Quantificationand Identification of Methane in Natural Gas Emissions Monitoring. J. Electrochem. Soc.
2021, 168 (9), 097506. https://doi.org/10.1149/1945-7111/ac2465.

Figure 1. Four electrode MPES response at 600 °C to CH4 in simulated air, low ethane simulated natural gas in air, and high ethane simulated natural gas in air, from left to right, respectively. Top row – ceria stabilized zirconia substrate. Bottom row – magnesia stabilized zirconia substrate.

Figure 1