Effect of pH value and temperatures on performances of Pd/C catalysts prepared by modified polyol process for formic acid electrooxidation

The highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X-ray, X-ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i-t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120°C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · g_Pd^-1) and stability for formic acid electrooxidation.