Electrochemical Decontamination of Platinum Nanocrystals and Its Electrocatalytic Performances for Methanol

Abstract

Platinum is the most widely used catalyst for fuel cells. The morphology of platinum has great influences on its catalytic activity and selectivity. Thus, the morphology controlled synthesis of platinum nanocrystals is attracting more and more attention in recent years [1-3]. Polyvinylpyrrolidone (PVP) is one of the most commonly used surface active agent for the morphology control of platinum nanocrystal. However, since PVP could strongly adsorb on the platinum surface and was difficult to remove thoroughly, the platinum surface couldn’t be utilized effectively and thus its catalytic activity will be reduced to a certain extent. This work focused on the decontamination of PVP on platinum by electrochemical treatment. Platinum nanocrystals was synthesized by colloidal method using chloroplatinic acid as the metal precursor and PVP K30 as a stabilizer. Spherical, cubic, octahedral and truncated octahedral platinum nanocrystals were obtained by adding different concentrations of silver nitrate to the above colloidal solution. The morphology of platinum nanocrystals was characterized by transmission electron microscope (TEM). It was found that the as-preparation platinum nanocrystals were well dispersed with a narrow size distribution. Electrochemical decontamination was applied to the platinum nanocrystals by short pulse potential step before electrocatalytic performance measurements. Repeating potential steps were set up between high voltage and low voltage. As the potential step proceeding, more and more surface sites were exposed, which could be confirmed from the more and more clear hydrogen and oxygen adsorption/desorption peak of the cyclic voltammograms (CV) (as shown in Fig. 1A). The CV curves stabilized eventually. The electrocatalytic activity of the electrochemical cleaned platinum nanocrystals was characterized by CV (as shown in Fig. 1B) and chronoamperometry measurements. It was found that truncated octahedral platinum nanocrystals showed the best catalytic activity for metha nol electrooxidation in 0.5 mol·L-1 H2SO4 + 0.5 mol·L-1 CH3OH solution. The methanol electrooxidation peak current was much higher than the current on platinum nanocrystals with other morphology. This study put forward a simple and effective electrochemical decontamination method of the platinum surfaces capped by PVP. Figure 1