An Electrochemical Measurement System Using Electrolyte Gel and a Flexible Printed Three-Electrode Sticker Device for in-Situ Measurements
Authors: Okamoto Yuri , Sakaeda Yuma , Loew Noya , Matsuhisa Naoji , Nagamine Kuniaki , Watanabe Hikari , Shitanda Isao , Itagaki Masayuki 
Published: December 2024

A sticker device for corrosion monitoring that enables accurate and simple electrochemical measurement of a three-electrode system by screen printing has been reported1). This sticker device has a reference electrode with liquid-junction and a counter electrode on a PET substrate having adhesive tape. They are formed by screen printing. The sticker device has a hole at the point of the working electrode, which can be used as the working electrode by attaching it to an object, for example a copper sheet. The measurement has been performed by dropping a solution onto the device. In this study, a sticker device with more flexibility and stretchability was fabricated using a polyurethane substrate and stretchable ink. In addition, electrolyte gels were investigated by combining these methods, electrochemical measurements on curved surfaces were performed.
The sticker device was fabricated by screen printing. Silver ink was used for the counter electrode and current-collecting wires, and KCl layers were stacked on top of the Ag and AgCl layers to form a saturated KCl/Ag/AgCl reference electrode. The electrolyte gel was fabricated by freeze-drying PVA. PVA was added to a KCl solution, heated and stirred at 120 °C and 1000 rpm for 1 hour, and then 20 g was divided into petri dishes of 8.5 cm in diameter. The gel was then frozen in a freezer and allowed to return to room temperature for gelation. Gels were fabricated with PVA at 5, 10, and 20 wt% and frozen for 3, 5, and 7 hours, and their physical properties were evaluated. The gels and sticker devices were combined in a measurement system to measure the dynamic potential polarization in the anodic direction. The device was attached to polished copper, and the electrolyte gel was adhered to the counter electrode of the device and the exposed copper (working electrode) for measurement. The results were compared with those obtained in a typical three-electrode electrochemical cell. Measurements on curved surfaces were performed by attaching copper foil to cylinders with curvatures of 0.25, 0.4, and 0.6.
The electrolyte gel containing 5 wt% PVA and with a freezing time of 5 hours had the best fluidity, adhesion to the sticker device and retention, so the electrolyte gel fabricated under these conditions was used for the measurements. Regarding the flexibility of the device, no cracks were observed in the electrodes or wiring even when the device was elongated and bent by about 20%, and electrochemical measurements were possible even when tensile stress was applied. For copper polarization measurements using electrolyte gel and sticker devices, slight diffrences were observed for polarization curves, which could be attributed to differences in gel adhesion and the structure of the liquid electrolyte and electrolyte gel. However, the polarization curves obtained using this measurement system in planar and curved surface showed similar behavior to those obtained with conventional electrochemical cells.
References
1)I. Shitanda, K. Miyazaki, N. Loew, R. Esaka, Y. Hoshi, M. Itagaki, Chemical Communications, 57, 2875-2878, (2021).

Figure 1