Hg microhemispherical electrodes

This section describes the deposition and characterization of a Hg hemisphere on Pt UMEs (3). Two methods of fabricating hemispherical Hg/Pt UMEs are described electrodeposition from an inorganic mercnry solution or from controlled contact of the Pt UME with a mercury drop. Electrochemical characterization can be performed using linear sweep voltammetry, amperometry (see Chapter 11) and SECM feedback experiments (see Chapter 12). 

Ideally, the solid support should be easily wet by and have a low solnbility in mercury. In the case of glassy carbon, the surface is poorly wet leading to the formation of scattered 

The solid support for the Hg hemisphere is a conventional Pt UME as reported in detail in Section 6.3.1 of this Handbook and other published work (10). 

A CHI Model 900 scanning electrochemical microscope (CH Instruments, Austin, TX) can be used to control UME tip potentials, obtain approach curves and monitor the tip to underlying substrate distance. Voltanunetric and SECM experiments can be performed either with the SECM head in a glove bag under positive pressure or the SECM cell covered with parafilm and in the presence of an argon blanket. Where SECM characterization is not possible, any potentiostat can be used to deposit and characterize the Hg/Pt UME. 

Mercury is deposited onto a Pt UME from a Hg2(N03)2 solution in a three-electrode setup and controlled by a potentiostat. A1 nun Pt wire serves as a counter electrode and a fritted 

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