The Au/Pd core-shell nanoparticles (NPs) were synthesized via galvanic replacement of Cu by Pd on hollow Au cores by adding different concentrations of Na2SO3 solution. It was found that the higher concentration of Na2SO3 that was used, the rougher the Au nanospheres became. However, the rougher Au surface may cause more defects in the Pd layers and decrease the catalytic abilities. The Au/Pd NPs synthesized using 0 M Na2SO3 (denoted as 0 M-Au/Pd NPs) have the smoothest Pd surface and demonstrate higher formic acid oxidation (FAO) activity (0.714 mA cm(-2), normalized to the surface area of Pd) than other Au/Pd NPs and commercial Pd black (0.47 mA cm(-2)). Additional electrochemical characterization of the 0 M-Au/Pd NPs also demonstrated lower CO-stripping onset and peak potentials, higher stability (8x improvement in stabilized oxidation current), and superior durability (by 1.6x) than the Pd black. In addition, a simple simulation of FAO was adopted to predict the anodic curve by including reaction intermediates of formate and hydroxyl. The 0 M-Au/Pd NPs were found to show higher formate and lower hydroxyl coverage than the Pd black. (C) 2013 Elsevier B.V. All rights reserved.