Carbon supported Pd-Pt-Cu trimetallic nanocatalysts for formic acid oxidation (FAO) are comparatively synthesized via different one-pot liquid-phase chemical reduction routes. Either sodium borohydride or ethylene glycol is employed as the main reducing agent, with the stabilizer opted from disodium ethylenediamine tetraacetate (EDTA), oleylamine, sodium citrate and urea. The trimetallic nanocatalyst synthesized with ethylene glycol and sodium citrate exhibits the most homogeneous nanoparticle dispersion and the highest alloying degree. Pd20Pt1Cu10/C-Cit shows the best electrocatalytic performance among all the tested electrocatalysts. Componential distributions on nanoalloy particles are distinguished through ex situ XPS, CO stripping and in situ ATR-IR measurements on interested nanocatalysts. The cheaper element Cu functions mainly as the "core filler" to expose a Pd and Pt-segregated active surface, and a deliberately controlled small fraction of Pt (versus Pd) on the surface minimizes the undesired dehydration of formic acid. In addition, a weak electronic effect from Cu and Pt may promote FAO on Pd. Surface restructuring with Pt agglomeration and partial Cu dealloying arising from a repeated potential cycling pretreatment degrades the performance of the ternary nanocatalysts. (C) 2013 Elsevier B.V. All rights reserved.