One problem of carbon supported Pd (Pd/C) anodic catalyst in direct formic acid fuel cell (DFAFC) is the poor electrocatalytic stability. Considering Pd metal can be dissolved in the acidic electrolyte, the effect of the addition of Pd2+ ions in the electrolyte on the electrocatalytic stability of Pd/C catalyst for formic acid oxidation was investigated. It was found that after the Pd/C catalyst is immersed in the electrolytes with 1.0 x 10(-4) M Pd2+ for 8 days, the electrocatalytic activity and stability of the Pd/C catalyst are higher than that of the Pd/C catalyst without immersing and with immersing in the electrolyte without Pd2+ ions. There are four reasons for obtaining high electrocatalytic performance of the Pd/C catalyst by Pd2+. (1) The existence of Pd2+ ions in the electrolyte could effectively inhibit the dissolution of Pd in the Pd/C catalyst. (2) Some Pd2+ ions would be adsorbed on the surface of Pd particles and then increase the roughness of the Pd particles. (3) Pd2+ ions adsorbed on Pd particles can make the intermediate of formic acid oxidation easy to be oxidized to CO2. (4) Pd2+ could be reduced to Pd under -0.2 V and 0.8V electrode potential. Then, the new active sites are generated constantly in the process of potential scanning. Therefore, this investigation suggested a new method to improve the performance of the Pd/C anodic catalyst in DFAFC. (C) 2012 Published by Elsevier Ltd.