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We report here the activated carbon and cobalt hexacyanoferrate composite,which is applied as the elec-trode materials in symmetric supercapacitors containing a 1.0 M Na2SO4 aqueous electrolyte.This novel material combines high specific surface area and electrochemical stability of activated carbon with the redox properties of cobalt hexacyanoferrate,resulting in maximum specific capacitance of 329 F g-1 with large voltage working window of 2.0 V.Electrochemical studies indicated that cobalt hexacyanoferrate introduces important pseudocapacitive properties accounting for the overall charge-storage process,especially when I ＜ 0.5 A g-1.At lower gravimetric currents(e.g.,0.05 A g-1)and up to 1.0 V,the presence of cobalt hexacyanoferrate improves the specific energy for more than 300％.In addition,to better under-standing the energy storage process we also provided a careful investigation of the electrode materials under dynamic polarization conditions using the in situ Raman spectroscopy and synchrotron light X-ray diffraction techniques.Interesting complementary findings were obtained in these studies.We believe that this novel electrode material is promising for applications regarding the energy-storage pro-cess in pseudocapacitors with long lifespan properties.