PEDOT/PEDOT-S Copolymer-Based Nonaqueous Solid-State Reference Electrode with High Electrochemical and Mechanical Stability

Abstract

Nonaqueous electroanalytical experiments require a stable and mechanically robust reference electrode (RE). The primary role of an RE is to maintain constant cell potential. Ag/Ag⁺ and Ag/AgCl are the most widely used REs in nonaqueous electrochemistry due to their robustness, but the disadvantages of chemical and ionic contamination and potential drifts from nonspecific Ag⁺ activity have caused a shift toward polymer back contact-based solid-state reference electrodes (SSREs). Most polymer-based nonaqueous REs, however, suffer from a lack of structural integrity, exhibit potential drifting, and have ill-defined potential. In this work, a self-doped poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene) sulfonated or PEDOT/PEDOT-S (S = sulfonated) polymer-based SSRE was fabricated with high mechanical durability and chemical stability. An unbound sulfonate anion in the EDOT-S polymer backbone of this SSRE increases chemical and mechanical stability. PEDOT/PEDOT-S electrodeposited stainless-steel wires with a commercial polytetrafluoroethylene (PTFE) coating have been fabricated and further optimized with an inner filling of 0.1 M TBAPF₆/acetonitrile solution. A potential drift of 2.65 μV/h for the SSRE without an inner filling solution and 1.72 μV/h for the SSRE with it (n = 3) vs Fc/Fc⁺ were achieved after testing for 14 days. Mechanical bending and twisting of the SSRE preserved the polymer coating, RE function, and mechanical stability. The SSRE with the inner filling solution has been successfully used in nonaqueous electroanalytical and electrolysis applications. The SSRE can be reused after storing without a supporting nonaqueous solution, allowing for the possibility of prolonged dry storage and easy shipping.