The electronic structure of poly(sodium 4-styrenesulfonate) intercalated graphite oxide (PSSGO) in the vicinity of the Fermi level was investigated using ultraviolet photoemission and inverse photoemission spectroscopies. The conduction band density of states for PSSGO is similar to that of graphite, indicating facile electron transfer from electrolyte ions to the PSSGO electrode in energy storage device applications. The in situ band gap of 1.9 eV observed was smaller than that of graphite oxide by 0.4 eV, helping to explain the high performance of electric double layer capacitor of PSSGO compared with graphite oxide. (C) 2013 Elsevier B. V. All rights reserved.