Nanoporous PtNi alloy thin film was demonstrated to effectively improve the thermal stability of cathode under high temperature fuel cell operation. The grain growth, which indicates the agglomeration of the nanoparticles, were constrained, as observed by comparing the surface morphologies and grain sizes in bulk of film between pure Pt and PtNi alloy cathodes. The constrained grain growth by alloying with Ni maintained the porosity in bulk of cathode film for sufficient cathode oxygen diffusion and adsorption/dissociation processes. Fuel cell using Pt-67-Ni-33 cathode better maintained the output current density than the cell using pure Pt cathode by 26% after 48 hours of continuous operation. (C) 2017 Elsevier Ltd. All rights reserved.