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The Development and Characterization of Inkjet-Printed Solid-State Ag/AgCl Reference Electrodes

Miniaturized solid-state reference electrodes (SSRE) with a stable potential are needed to enable novel application scenarios of potentiometric sensing. Inkjet printing has recently been highlighted as a prospective technology for the development of such electrodes in a high-throughput and cost-effective manner [1]. We present here the first steps in the development of inkjet-printed Ag/AgCl SSREs. Two different electrode designs were tested: First, a disk silver electrode was chemically chlorinated using iron(III) chloride and surface coated with a poly(vinyl butyral) (PVB) reference membrane [1] – RE1. Second, a reference Ag/AgCl paste was formulated based on AgCl reduction in a PVB solution [2] – RE2, which enabled development on non-silver (glassy carbon) disk electrodes. An innovative intense pulsed light (IPL) photoreduction technique was applied for AgCl reduction in the paste. The conditions of chemical chlorination and IPL photoreduction parameters were optimized, as well as the required volumes of the reference membranes and conditioning times. The electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The response of the electrodes in aqueous solutions of various salts, including KCl, NaNO3, NaCl, and CaCl2 of different concentrations was examined, as well as the electrodes’ response to pH changes. In all cases, an acceptable voltage response was achieved, and both types of electrodes were stable over a wide pH range. Further on, comparative characterization of a commercial ion-selective electrode with prepared SSREs against a conventional (internal electrolyte based) double junction Ag/AgCl electrode was performed, yielding similar sub-Nernstian slopes for all systems. Finally, the optimized reference membranes were transferred onto planar electrodes fabricated by inkjet printing of silver and graphene inks and characterized correspondingly. Acknowledgment This work was funded by the Croatian Science Foundation under grant UIP-2020-02-9139. References 1. A. Moya, R. Pol, A. Martínez-Cuadrado, R. Villa, G. Gabriel, M. Baeza, Stable Full-Inkjet- Printed Solid-State Ag/AgCl Reference Electrode, Anal. Chem. 2019, 91, 24, 15539–15546. 2. T. Guinovart Gaston, A. Crespo, F. X. Rius, F. J. Andrade, A reference electrode based on polyvinyl butyral (PVB) polymer for decentralized chemical measurements, Anal. Chim. Acta 2014, 821, 22, 72–80.

solid-state reference electrode (SSRE) ; polyvinyl butyral (PVB) ; potentiometry

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