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Beyond Capacitance: Rethinking the Stability of Ion-Selective Electrodes With Carbon-Based Solid Contacts.
Emily E A Robinson1, Yevedzo E Chipangura1, Hiroki D Coyle1
1Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States.
Analytical Chemistry
|November 13, 2025
Summary
Large-surface-area carbon materials used in ion-selective electrodes (ISEs) can suffer from potential drift due to unexpected redox reactions. Suppressing these reactions is key for stable, calibration-free electrodes.
Area of Science:
- Electrochemistry
- Materials Science
- Analytical Chemistry
Background:
- Large-surface-area carbon materials are widely used as solid-contact (SC) materials in ion-selective electrodes (ISEs) due to their high non-faradaic capacitance, which is linked to potential stability.
- However, single-walled carbon nanotube (SWCNT) SC interfaces exhibit slow potential discharge caused by unexpected redox processes, leading to potential drift and limiting long-term SC-ISE stability.
Purpose of the Study:
- To investigate and differentiate redox reactions from charge redistribution artifacts in various high-surface-area carbon materials used as SCs.
- To compare the stability and redox behavior of nanographite, mesoporous carbon nanospheres (MCN), and SWCNTs under potentiometric conditions.
Main Methods:
- Employed a sequential chronopotentiometry (CP), chronoamperometry (CA), and open-circuit potential (Pot) measurement sequence (CP-CA-CP-Pot-CP).
- Applied small voltages to mimic real-life potentiometer input impedance effects.
- Conducted contact angle measurements to assess surface oxidation after prolonged voltage application.
Main Results:
- MCN and nanographite interfaces showed no capacitance changes after small voltage applications, unlike SWCNT interfaces.
- Contact angle measurements indicated surface oxidation in SWCNTs, MCN, and nanographite after one day of small voltage application, with nanographite being most sensitive to oxygen.
- Discharge mechanisms differ significantly across carbon materials, demonstrating that high capacitance alone does not ensure electrode stability.
Conclusions:
- High capacitance in carbon solid contacts does not guarantee electrode stability; minimizing redox reactivity is crucial.
- The development of high-surface-area carbon materials with suppressed redox activity is essential for advancing SC-ISEs towards improved long-term stability and calibration-free operation.
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