Renewable electrode surfaces for monitoring CO2 based on adsorptive accumulation of catalyst

Adsorptive accumulation of the catalyst [Ni(II)Cyclam]2+ on the surface of the mercury electrode is used to prepare a catalytically active electrode surface for the reduction of CO2. When argon used for the deoxygenation of the solution is replaced by CO2 the voltammogram, recorded following adsorptive preconcentration of [Ni(II)Cyclam]2+, exhibits a large catalytic peak at the potentials of the complex reduction. The dependences of the peak current on the concentration of the complex in the solution and on the preaccumulation time reveal that the adsorbed form of the reduced Ni(I) complex and not the form dissolved in the solution is the true catalytically active species in the process studied. Concentrations of the complex in the solution in the 10−8–10−7M range are sufficient to obtain well-developed signals of CO2 catalytic reduction. At constant catalyst concentration, the peak current is controlled by diffusion of CO2 to the electrode and increases linearly with increasing concentration of CO2 in the range 1 × 10−4–4 × 10−2 M. Two versions of the procedure based on either linear scan or normal pulse voltammetries are proposed for monitoring changes in the CO2 level in the solution.