Electrochemical study of the Pt nanoparticles size effect in the formic acid oxidation

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) provided interesting information about the particle size effect during HCOOH electro-oxidation. They were evaluated Pt nanoparticles between 1.5 and 3.7nm (From Etek Co.). Formic acid reaction shows strong particle size effect, which was correlated with surface condition. CV showed that under certain conditions small particles might have a better catalytic activity than the larger ones. The latter, was supported by EIS which indicate a higher blockage of active sites on larger particle. The co-adsorption of formate and CO on Pt have been postulated as the species which poisoning the catalyst's active sites inhibiting the oxidation of formic acid. The surface blockage was observed as a negative differential resistance (NDR) response. The potential from which NDR appears is higher when the nanoparticles sizes of Pt decrease due to a less effective inhibition process.