Diodes composed of a nanoparticulate composite of poly(3,4-ethylenedioxythiophene) and a Cu-Cu2+ redox couple in a poly(ethylene oxide)-LiBF4 polymer-electrolyte matrix between Ag and Zr electrodes show rectifications in excess of 50000 at applied fields of 4 V These large changes are considered to arise from both rectification at the Zr/ZrO2 composite interface and from the switching of the composite material between two conductivity states by the application of a low potential field. preparation and electrochemical characterisation of these novel active devices are discussed.