Effects of the Mercury ion Concentration on the Preparation of Mercury Deposits on Platinum Micro-Disk Electrodes

摘要

In this paper, the effect of mercury ion concentration on the preparation of mercurymicroelectrodes fabricated on a platinum microdisk of 10 #mu#m radius was studied. The preparation of the mercury microelectrodes was followed by chronoamperometry, and the measurements were performed in Hg_2( NO_3)_2 solutions with concentrations over the range 0.1-0.25 mM. The mercury microelectrode size was referred to as h/a, where h is the height of the mercury deposit and a is the radius of the inlaid microdisk. The mercury microelectrodes investigated had h/a values over the range 0 - 2. The results obtained indicated that from concentrated mercury ion solutions (> 0.5 mM) the mercury growth was somehow erratic due to the coalescence of small mercury droplets. On the other hand, from dilute solutions (< 0.5 mM), the mercury deposits new smoothly. Under the latter conditions the geometric coefficient k, which characterises the steady state diffusion limiting current expression at a mercury microelectrode, was determined with good accuracy (within 5% error) from the chronoamperometric curves recorded during the mercury microelectrode preparation. In general, the coefficient k was calculated from theoretical expressions derived for a sphere cap and spheroidal geometry, which may model the shape of the mercury deposits. The comparison between theoretical and experimental k values suggested that both geometries equally modelled the experimental mercury deposit obtained. Finally, for the sphere cap geometry an algebraic expression relating k and h/a was derived fro an easier k evaluation from experimental h/a values.