A method of electrolytic SnP2O7 coating on Pt was investigated in SnCl2 and H3PO4 aqueous solution. The coating films were further annealed and characterized by Fourier transform infrared spectroscopy, thermogravimetric-differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The results revealed the as-coated film was composed of hydrated SnHPO4 and H3PO3, the evaporation of physically adsorbed water between 20 and 130 degrees C, the evaporation of extra (unreacted) H3PO3 around 180 S C, which was gradually followed by the phase transformation into SnP2O7 which finished at 900 degrees C. The SnP2O7 coating film composed of agglomerated nanoparticles (20-30 nm) with a thickness about 160 nm revealed the adherent interface on the substrate. (c) 2005 The Electrochemical Society.