Effect of Surface Morphology and Pore Structure on the Water Electrolysis, O2 Evolution Activity of Sb-Doped SnO2 Supported IrO2

Nanoparticle IrO₂ supported on Antimony doped Tin Oxide (ATO) is a very active electrocatalyst for the oxygen evolution in polymer electrolyte water electrolysis. Using the modified polyol method [A. Marshal and et al. /Material Chemistry and Physics, 94 (2005) 226] nanoparticles of IrO₂ were synthesized and deposited on commercial antimony doped tin oxide (ATO). This synthesis involves the reduction of a metal precursors (IrCl₂) in ethylene glycol containing a suspension of ATO. Nanoparticle catalysts were characterized by cyclic voltammetry (CV) and steady state polarization analysis in 0.5 M H₂SO₄ solution. The CV voltammograms for IrO₂/ATO catalyst showed clear broad peaks for oxidation and reduction of IrO₂, with peaks at 0.72 V and 0.82 V respectively.   The catalyst morphology, surface area and the pore structure were studied using BET nitrogen physisorption, mercury porosimetry, Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM). The BET surface area was found to be 59.4 m²/gr and the total porosity (interparticle and intraparticle porosity) of the catalyst was found to be 4.45 %. A narrow particle size distribution for the IrO₂ phase in the range of 1 to 3 nm was determined by examining and analyzing the TEM images. X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) were also done to provide information on the crystal structure and thermal properties.   Polarization curves for membrane electrode assemblies (MEAs) fabricated using this catalyst will be presented. The importance of the pore structure in providing good catalytic activity and mass transport in the two-phase flow process will be discussed.