Solid-state electrochemical capacitors were prepared by combining composite electrodes based on a carbon paper/carbon nanotubes assembly coated with a layer of a pseudocapacitive electrode materials such as manganese dioxide or ruthenium dioxide separated by a solid state membrane to support the electrolyte. The composite electrodes were prepared by using a simple slow filtration technique. The electrolytes consist of ion-exchange membranes (such as Nafion or CMX from Neosepta) that are impregnated with an appropriate electrolyte. Acidic and neutral electrolytes were investigated in this work. Symmetrical electrochemical capacitors were prepared with two similar electrodes. Different combinations of electrode and membrane were assembled and characterized electrochemically by cyclic voltammetry and constant current charge/discharge cycling. The effect of cycling rate and temperature (from – 60 to + 60 °C) on the electrochemical performance of the solid-state electrochemical capacitors was evaluated.