Bimetallic catalysts have attracted enormous attention with their enhanced electrocatalytic properties in fuel cells. Herein a series of silsesquioxane (POSS) stabilized platinum-palladium (PtPd) alloy nanoparticles (NPs) with morphology evolution were facilely synthesized with the co-chemical reduction using formaldehyde as the reductant. By varying the ratio of Pt to Pd, the PtPd alloy NPs evolved from truncated octahedrons to octahedrons, and triangular nanoplates. The mechanism of morphology evolution is that Pt and Pd could self-assemble on POSS to form PtxPd1-x intermediates with different Pt/Pd ratios. In addition, formaldehyde could selectively bind to the {1 1 1} facets of Pd to control the growth rates of different facets and help PtxPd1-x intermediates with different Pt/Pd ratio grow into different morphology of PtxPd1-x alloys. The morphology tuning endowed the PtPd alloy NPs superior performance for formic acid electrooxidation. Compared with Pt, Pd NPs, and commercial Pt/C catalyst, the PtPd alloy NPs displayed larger electrochemically active surface area, enhanced electrocatalytic activity and durability toward oxidation of formic acid, and increased CO tolerance. This work suggested that modification of catalytic activity through morphology tuning with composition adjustment might provide some new pathways for the design of promising catalysts with advanced performance. (C) 2017 Elsevier Inc. All rights reserved.