This study investigates several CNT-supported Pd-based catalysts and compares their morphological as well as electrochemical characteristics for formic acid electro-oxidation. Pd/C catalysts are prepared via various impregnation methods, using different reaction media or reducing agents. The average mean particle sizes of the precipitated Pd vary from 2.6 nm to 18.0 nm. It is further shown that the particle size of Pd/C dispersions can be easily controlled by changing the solvent and experimental conditions during the preparation procedure. Measurements of catalytic activity by using cyclic voltammetry reveal strong particle size dependence of the anodic peak current density. The electro-oxidation of formic acid may be kinetically-controlled or diffusion-controlled regarding the Pd morphological characteristics. (C) 2013 Elsevier B.V. All rights reserved.