The electrochemical oxidation of H2O2 at platinum rotating disc electrodes and microelectrodes was studied as a function of phosphate buffer concentration in the range 0-100 mM and pH from pH 4 to pH 10. The results were interpreted in terms of development of a surface binding site for H2O2 from a precursor site through interaction with H2PO4- from the electrolyte. In the absence of phosphate an alternative binding site mechanism was evident. The precursor site was shown to be inhibited by protons at low pH producing an inactive site.