A combined µ-mercury reference electrode/Au counter-electrode system for microelectrochemical applications

Different types of mercury-based µ-reference electrodes (Hg/Hg2SO4/Na2SO4, Hg/Hg2(CH3COO)2/NaCOOCH3) have been developed following the concept of agar-based µ-reference electrodes. Mercury was electrochemically deposited onto a gold wire to form an amalgam. The corresponding mercury salt was formed electrochemically at the surface. This electrode can be inserted into a capillary that is filled with the electrolyte of interest. To simplify the handling of this µ-reference electrode, to reduce diffusion and to avoid leakage, the electrolyte was immobilised with agar. A 250-nm-thick gold layer on the outer surface of the capillary of the reference electrode served as counter-electrode. The electrochemical behaviour of reference electrodes and counter-electrodes were proven by micro-polarisation curves, electrochemical impedance spectroscopy, potential transients and cyclic voltammetry.