Simplex optimization of electroreduction of oxygen mediated by methyl viologen supported on zeolite-modified carbon paste electrode

Abstract

By using the methyl viologen—oxygen system as a model, zeolites Y and A were shown to be promising as supports for electrocatalysts, and perhaps as sites for preconcentration of substrates as well. Simplex optimization was used to reach a maximum catalytic peak current for the reduction of oxygen using a modified electrode consisting of carbon paste mixed with the sodium form of zeolite Y. The electrochemistry was carried out in aqueous lithium perchlorate solution buffered at pH 7.00. There were four parameters varied to give a maximum peak current due to oxygen reduction: 1. concentration of methyl viologen in solution; 2. percentage (by mass) of Y zeolite mixed into carbon paste electrode; 3. time of exposure of zeolite-modified electrode to viologen solution prior to voltammetric experiment; 4. duration of oxygenation of solution prior to experiment. Peak current for reduction of oxygen showed a maximum with respect to parameters 1 and 2. Peak currents increased then leveled off as parameters 3 and 4 were increased. The optimal response was obtained when carbon paste electrode containing 49 wt% zeolite Y was immersed in a 32 mM solution of methyl viologen in aqueous electrolyte solution saturated with oxygen. An equilibration period of 46 min was required to achieve an optimal degree of ion exchange of methyl viologen cation radical into the zeolite prior to the electrochemical experiment. In addition to optimizing peak current, the simplex method allowed conclusions to be drawn about the interrelationships among parameters in the electrochemical system.