Mesoporous platinum films consisting of patterned holes were deposited on yttria-stabilized zirconia via nanosphere lithography. Film morphology evolution was investigated using atomic force microscopy after annealing in either H-2/N-2 forming gas or pure oxygen. Extracted Pt surface diffusion activation energies were 1: 16 and 1: 22 eV for forming gas and oxygen environments, respectively, with a smaller diffusivity prefactor for the latter ambient. This difference is attributed to reduced platinum surface mobility due to bound surface oxygen atoms, as confirmed by XPS. At 650 degrees C, Pt crystallite migration in the oxygen environment also contributed to film break-up. Implications for solid oxide fuel cells are discussed. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3609257] All rights reserved.