Planar Ag/AgCl Reference Electrode for Electrochemical Agronomic Sensors

Robust, stable, and portable planar reference electrodes that perform analogous to conventional Ag/AgCl reference electrodes are of paramount importance for any electrochemical soil sensors, such as soil pH and NPK sensors. This letter reports the fabrication and characterization of planar Ag/AgCl reference electrode (PARE) with graphene conductive ink (GCI) as a protective layer. For its application in soil agronomy, the fabricated PARE is exclusively tested in soil solutions with different pH, 1 M KCl and pH buffer solutions. The fabricated PARE exhibited a drift of +/- 3 mV in pH buffers and is relatively insensitive to changes in pH. The drift in the open circuit potential of the PARE without GCI is found to be +/- 10.02 mV for a period of 72 h in 1 M KCl, whereas the drift with GCI is significantly reduced to +/- 0.98 mV resulting in a stable response. Furthermore, electrochemical impedance spectroscopic studies are performed to examine the protective layer's contribution to sustaining electrode stability over extended periods of time. Finally, the PARE is proven to be stable, exhibiting minimal drift for varying soil pH levels, indicating its potential as a stable reference electrode for agronomic applications.