Technologies are generally described for electrochemical capacitor devices. Some example electrochemical capacitor devices may include a composite electrode that includes an electrode substrate coupled to a polymeric electrochemical layer. The polymeric electrochemical layer may include: a conductive polymer electrically coupled to the electrode substrate; a solid state, ionically conductive electrolyte polymer; and non-conducting cross-links that covalently link the conductive polymer and the electrolyte polymer. Various example electrochemical capacitor devices may be constructed by laminating two of the composite electrodes against opposing sides of an ionically conducting separator membrane, and contacting the composite electrodes and the separator membrane with a liquid electrolyte. Some example electrochemical capacitor devices may display favorable performance such as symmetric charge storage, non-Faradic charge storage, and/or similar or greater capacity compared to carbon based systems.