Electrolytic graphene oxide and its electrochemical properties

• Oxidation-controlled and contaminant free graphene oxide (eGO) electrodes were prepared.
• Electrochemical reduced eGO (r-eGO) had high double-layer charging capacitance.
• The r-eGO had high electrocatalytic activity for oxygen reduction reaction.
• Metal oxides electrodeposited on r-eGO increased the capacitance and catalytic activity.

Low-cost graphene oxide (GO) and related materials are considered supermaterials because of their unique and excellent properties for many applications that are greatly affected by oxidation degree and dopants (impurities). Conventional GO prepared by the multistep Hummers’ method is unable to control degree of the oxidation and impurities. Here, we demonstrate a facile one-step method for preparing pure GO on graphite substrates [i.e. glassy carbon (GC), highly oriented pyrolytic graphite-basal plane surface (HOPG-b), and highly oriented pyrolytic graphite-edge surface (HOPG-e)] by electrolysis in pure water under high voltage; the resultant GO is called electrolytic GO (eGO). The degree of oxidation in eGO can be easily controlled by adjusting the applied voltage and the electrolysis time, and small-sized eGO can be obtained by using a counter tip electrode on the substrate during the electrolysis. Photoelectrochemically reduced eGO (r-eGO) had a large double-layer charging capacitance and high electrocatalytic activity for the oxygen reduction reaction (ORR), and acted as an n-type semiconductor electrode. The r-eGO formed on HOPG-b had larger capacitance and higher activity for ORR than that on HOPG-e. The excellent properties of r-eGO were due to carbon defects and/or OH groups produced by the reduction of epoxide groups formed at the basal plane, as evidenced by X-ray photoelectron spectroscopy and Raman spectroscopy. The photoelectrochemical deposition of metal oxides or hydroxides on r-eGO increased the capacitance and catalytic activity of the material.