Simultaneous impedance measurements of two one-face sealed resonating piezoelectric quartz crystals for in situ monitoring of electrochemical processes and solution properties

Through admittance measurements of two piezoelectric quartz crystals in parallel on one impedance analyzer and then non-linear fitting according to an equivalent circuit of two parallel Butterworth-Van Dyke circuits, we have simultaneously obtained accurate and precise impedance responses of two one-face sealed crystals to changes in solution density and viscosity, temperature, conductance, and/or electrode mass. A series of sucrose aqueous solutions, ferri-/ferrocyanide redox switching, hot water cooling, a series of NaClO₄ aqueous solutions, bovine serum albumin adsorption and silver electrodeposition/stripping were selected as model systems for such purposes. Galvanostatic charging/discharging reactions at positive and negative poles in a Ni-Zn battery were synchronously monitored, with some quartz crystal microbalance (QCM) insights into the second reduction process of nickel hydroxide film. In all cases, the crystal immersion angle effect was found to be negligible. The present method as a versatile one is highly recommended for informative two-electrode monitoring of two concurrent chemical or biological events, or for check and/or compensation of effects due to solution density, viscosity, temperature and/or conductance during QCM researches.