Electrochemical current rectification with cross reaction at a TEMPO/viologen-substituted polymer thin-layer heterojunction

Totally reversible redox-active polymers, 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl functionalized polyacrylic acid (PTAm-A) and poly(tripyridiniomesitylene) (PTPM), both of which possessed rapid charge transport properties in an aqueous electrolyte, were applied to a polymer-sandwiched device to offer an electrochemical current rectification functionality. Single-layer and bilayer devices were fabricated employing the PTAm-A and/or PTPM thin layer(s) as charge transport media. Single-layer devices with a 1 cm² electrode area demonstrated large currents in the order of several milliamperes, which were established by redox mediation based on a fast electron self-exchange reaction between adjacent redox sites in the polymer layers. A current-voltage response obtained from the bilayer device exhibited a rectification effect due to thermodynamically favoured cross reaction at the polymer/polymer interface, retaining the large current densities. The observed currents were comparable to those predicted from the diffusion-controlled charge transport kinetics. Potentiostatic measurements revealed that the rectified current readily achieved a steady state in response to the applied voltage. These results demonstrate that the PTAm-A/PTPM thin-layer heterojunction enabled a large current rectification based on the redox mediation process, providing insight into ideal charge flow systems in various electrochemical devices.