Spontaneous modification of glassy carbon surface with anthraquinone from the solutions of its diazonium derivative: An oxygen reduction study

The spontaneous grafting of anthraquinone (AQ) to glassy carbon (GC) from solutions of its diazonium derivative and the resulting electrocatalytic properties are reported. Surface modification was performed in acetonitrile and in aqueous solutions of various pH and a strong bonding of AQ to the surface is in evidence as the modified electrodes withstand long-term sonication in acetonitrile. The dependence of AQ coverage on immersion time was studied by cyclic voltammetry. The attached AQ showed a quasi-reversible redox-behaviour in 0.1 M KOH. The electrocatalytic properties of these electrodes and the corresponding kinetic parameters for oxygen reduction were determined using rotating disk electrode (RDE) voltammetry and the results were analysed using a surface redox catalytic cycle model for quinone modified electrodes. O2 reduction reaction parameters were compared with those obtained with electrochemically grafted electrodes. It is concluded that the two grafting methods give similar results and in particular, the rate constant of the reaction between the semiquinone and molecular oxygen was very close for electrografted to spontaneously modified electrodes. The different possible heterogeneous reaction mechanisms are discussed by comparison with dediazoniation reactions in solution and the involvement of the Gomberg–Bachmann dediazoniation mechanism in the generation of aryl radical for surface functionalisation is proposed.