DETERMINATION OF POROUS VOLUME OF A THIN LAYER USING QCM-D TECHNIQUE

Micrometer and nanometer order thin layers are nowadays common in a vast spectrum of scientific fields, including optical and electronics applications as well as various nanometric devices. In electrochemical devices for energy storage and conversion, the electrode porosity plays an important role, especially when the desired reaction occurs on the surface. Yet, a high surface area fraction may also facilitate an occurrence of competing parasitic reactions. Currently, common techniques for surface area evaluation are based on analyses of gas adsorption isotherms (e.g., BET) or mercury porosimetry. These methods, however, are suitable for bulk, but limited for thin layer analysis.

We proposed to use Quartz Crystal Microbalance with Dissipation (QCM-D) for measurement of thin layers` pore volume, and to establish clear criteria for pore volume analyses. The conventional QCM method provides gravimetric information for thin layers up to nanogram order. The QCM-D instrument allows simultaneous measurement of several overtones of the resonance frequency, which increases the detection sensitivity and accuracy. However, deposition of a thin porous layer on top of the quartz sensor is not trivial at all. To show applicability of the method, we created model porous layers of a rigid electrode with controlled porosity, by repeated alloying/dealloying of a zinc foil and the gold electrode sputtered on top of the quartz crystal. After several cycles, the electrode was characterized by HR-SEM and AFM; then the pore volume was measured in the QCM-D.

Encouraged by the obtained result, we plan to apply the method for complex porous systems such as carbons for energy storage devices.