Electrode reactions in Cu–Pt coated ionic polymer actuators

Composite actuators consisting of sheets of the solid polymer electrolyte (similar to Nafion®) with Cu2+ counter ions inserted and coated with platinum and copper metal layers (so-called ionomeric polymer–metal composites; IPMCs) have been synthesised and their electromechanical performance upon actuation has been monitored. Resistance measurements on the electrodes show that the electrical conductivity of the membranes metal surface increases on the cathode side during the actuation process, contradictory to the situation when Cu is absent from the metal coating. This phenomenon is explained by the subsequent reduction of Cu2+ ions on the cathode upon actuation; Cu layer growth in this side prevents it from cracking and decreases its electrode resistance. The phenomenon opens up for longer lifetimes for Cu-based IPMCs. However, additional problems with Cu layer oxidation and Cu dendrite growth on the electrodes should be considered.