Attenuation of Redox Interference in RuO₂ pH Sensor Using a Ta₂O₅/Nafion Multilayer Architecture

Area of Science:

• Electrochemistry and Sensor Technology
• Materials Science for Chemical Sensing
• Surface Chemistry and Interface Engineering

Background:

• Solid-state pH sensors offer advantages over traditional glass electrodes but face challenges with redox-active species.
• Metal-oxide based sensors, particularly ruthenium oxide (RuO2), are susceptible to interference from dissolved oxygen, ascorbic acid, and sulfides.
• This interference limits the practical application and reliability of these advanced pH sensing systems in complex environments.

Purpose of the Study:

• To investigate and mitigate the effects of redox interferents on solid-state RuO2 pH sensors.
• To elucidate the mechanism by which Ta2O5/Nafion overlayers suppress redox interference and enhance sensor stability.
• To demonstrate the improved performance of modified RuO2 electrodes in complex sample matrices.

Main Methods:

• Fabrication of solid-state RuO2 pH-sensitive electrodes on Al2O3 substrates using laser micro-etching and RF sputtering.
• Application of Ta2O5/Nafion overlayers to the fabricated RuO2 electrodes.
• Systematic investigation of redox interferents, including dissolved oxygen, potassium permanganate, and ascorbic acid, on electrode performance.

Main Results:

• Unmodified RuO2 electrodes exhibited excellent intrinsic pH sensing characteristics (near-Nernstian sensitivity, wide linear range, low hysteresis, minimal drift).
• Ta2O5/Nafion modified electrodes demonstrated significantly enhanced stability and suppressed potential fluctuations caused by redox species.
• Ascorbic acid interference was particularly mitigated by the Ta2O5/Nafion overlayer, improving measurement reliability in complex samples.

Conclusions:

• The Ta2O5/Nafion overlayer effectively suppresses redox interference, particularly from ascorbic acid and dissolved oxygen, in RuO2-based solid-state pH sensors.
• This modification strategy significantly enhances the robustness and reliability of pH measurements in complex electrochemical environments.
• The findings present a promising approach for advancing the practical application of solid-state metal-oxide pH sensors.