Studies indicated that the existing carbon supported Pt-based nanoalloys may exhibit instability and lose activity under acidic conditions due to particle aggregation, leaching/dissolution of the non-precious metals and carbon corrosion, which impeded the practical use of these nanomaterials for fuel cell electrocatalysts. This work presents a polyaniline (PANI)-confined space annealing strategy to efficiently promote the stability and activity of solution phase synthesized PtNi nanoparticles. By virtue of an in situ formed PANI coating layer, PtNi NPs can be developed to be more stable and active at thermal annealing process without serious agglomeration. Simultaneously, high temperature forces the carbonization of PANI, featuring the final obtained PtNi NPs with a nitrogen-doped carbon (NC) coating layer. XPS analysis attributed the enhanced catalytic performance of as-constructed PtNi/C@NC composite to the unique electronic interaction between Pt atoms and NC outer layer, which is beneficial for stabilizing PtNi NPs under fuel cell working condition. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.