The current arising from a reversible redox reaction involving soluble species occurring at a microelectrode may be increased by moving a large electrode at open circuit close to the microelectrode. This phenomena is readily explained. The product of the electrochemical reaction at the microelectrode diffuses the short distance to the nearest part of the macroelectrode and alters the concentration of the redox species at this location on the macroelectrode, compared to other locations at the electrode surface. In this situation, the macroelectrode behaves as a shorted concentration cell and attempts to reduce the concentration aberration caused by the reaction occurring at the microelectrode. This is accomplished by producing more of the original reactant for the microelectrode. This, in turn, increases the flux of reactant to the microelectrode and, therefore, also the current at the microelectrode.
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