2.3 Electrochemistry of Bulk Superconducting Electrodes
Electrochemical measurements
on high-temperature superconductors have been the focus of numerous
studies1,
2, 5-8, 12-22 the majority of which have studied the electrochemistry of
bulk ceramic electrodes. Typically, a ceramic pellet is encapsulated
in an epoxy matrix. Due to the high reactivity with water, aqueous
electrochemistry has yielded poor voltammetry.12, 19, 20 In contrast, non-aqueous electrochemical methods have produced
voltammetry similar to that of noble metal electrodes. The acquisition
of well-behaved voltammetric response requires attention to the following
two important issues: the polycrystalline electrode must be properly
resurfaced and steps must be taken to prevent the formation of a
corrosion layer. Improper resurfacing techniques1, 2, 18 cause the response to be dominated by resistive and capacitive
contributions. Several strategies to obtain a fresh electrode surface
can be employed such as razor blade cleaving, sanding with coarse
sandpaper, and resurfacing with a diamond scribe in an inert atmosphere
glovebox. Common procedures for resurfacing noble metal electrodes
such as polishing the surface with Al2O3 /
H2O paste and cycling the potential of the electrode in
acidic solutions prove harmful to the superconductor’s surface. In
addition to requiring a fresh surface; dry, nonprotic solvents must
then be used for electrochemical solutions. Since surface corrosion
of YBa2Cu3O7-x plays a major
role in the electrochemical response of bulk electrodes, 2, 6, 8, 18 even small amounts of water can significantly hinder electron
transfer. When the electrode is resurfaced properly and care is
taken to eliminate water exposure, an electrochemical response comparable
to that of Pt is obtained.
