Partial oxidation of carbon nanotubes (CNTs) in mixed HNO₃ and H₂SO₄ is commonly used for the preparation of polymer-CNT composites. This procedure, however, emits toxic NO_x fumes, making it difficult for commercial scale-up. Herein we report an environment-friendly new method which utilizes mixed H₂O₂ and H₂SO₄ to partially oxidize CNTs to produce composite electrodes with polypyrrole (PPy). With the aid of Raman, Fourier Transform Infrared, and X-ray photoelectron spectroscopic techniques, the physiochemical properties of the CNTs prepared from H₂O₂ aided oxidation were compared with those CNTs treated in HNO₃ aided oxidation. Furthermore, through cyclic voltammetry, electrochemical impedance spectroscopy, and electrochemical quartz-crystal microbalance, the interaction of the doping anions (Cl^-, SO₄^2-, etc.) with partially oxidized CNTs were studied and used to explain the performance of different PPy-CNT composites. Results showed that the capacitance of the composite with CNTs treated by H₂O₂ aided oxidation (ca. 156.0 F/g) was comparable to that with CNTs treated by HNO₃ aided oxidation (ca. 163.0 F/g). Furthermore, the need for critically appraising the charge storage mechanism on the carbons used in making the PPy-CNT composites is emphasized, and general observations that various oxygen containing functional groups could contribute in different ways to the observed charge storage mechanism of both the oxidized CNTs and their corresponding polymer composites were also explained. It can thus be predicted that the H₂O₂ aided partial oxidation of CNTs is suitable for producing high performance polymer composite electrodes, and the new process is promising for commercial scale-up with low environmental impact.

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ACKNOWLEDGEMENT: This work received funding from the International Doctoral Innovation Centre, Ningbo Education Bureau, Ningbo Science and Technology Bureau, and the University of Nottingham, and Ningbo Municipal Government (3315 Plan and 2014A35001-1).