Electrochemical Cleaning of Polyvinylpyrrolidone-capped Pt Nanocubes for the Oxygen Reduction Reaction

Preparation of shape-controlled nanoparticles requires the use of surfactants and capping agents that need to be removed from the metallic surfaces without loss of surface quality. For the synthesis of Pt nanocubes we used polyvinylpyyrolidone (PVP) as capping agent and silver ions as structure-directing agent in ethylene glycol (EG). Our synthetic route produced around 80% of Pt nanocubes with an edge length of around 6 nm. The Pt nanocubes were characterized by TEM, EDX, XRD and TGA. Only a negligible amount of silver was found in the Pt nanocubes. Based on the TGA results, we revealed that the nanocubes were surrounded by PVP in form of a polymer shell. To remove the PVP from the surface of the Pt nanocubes before application as electrocatalyst, we studied the effects of the electrochemical cleaning at different upper potentials (0.8,1.0,1.2 and 1.4 V/RHE) and pH values (pH1 and pH13). To evaluate the effectiveness of the cleaning process, we determined the electrochemically active surface area (ECSA) and the catalytic activity of the cubic Pt nanoparticles for the oxygen reduction reaction. We showed that the electrochemical cycling in 0.1 M NaOH was not appropriate to oxidize and to remove the adsorbed PVP from the Pt surface. The highest effect on the ECSA and ORR activity for the treated Pt nanocubes was obtained by electrochemical cycling up to 0.8 V/RHE in 0.1 M HClO4. More interestingly, the cubic structure of the nanoparticles was preserved after the electrochemical cleaning in the entire potential range. (C) 2017 Elsevier Ltd. All rights reserved.