Surface Activation of Pt Nanoparticles Synthesised by "Hot Injection" in the Presence of Oleylamine

• Published in: Chemistry : a European journal 2015-09, Vol.21 (36), p.12694-12701
• Main Authors: Humphrey, Jo J. L., Sadasivan, Sajanikumari, Plana, Daniela, Celorrio, Verónica, Tooze, Robert A., Fermín, David J.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloids; electrocatalysis; Nanoparticles; Nanostructure; Oxidation; Platinum; supported catalysts; surface activation; Surface chemistry; Synthesis; Thermogravimetric analysis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201501496

Oleylamine (OA) based “hot injection” colloidal synthesis offers a versatile approach to the synthesis of highly monodisperse metallic and multi‐metallic alloyed nanostructures in the absence of potentially toxic and unstable phosphine compounds. For application in heterogeneous catalysis and electrocatalysis, the adsorbed OA species at the metal surfaces should be effectively removed without compromising the structure and composition of the nanostructures. Herein, we investigate the removal of OA from colloidal Pt nanoparticles through 1) “chemical methods” such as washing in acetic acid or ethanol, and ligand exchange with pyridine; and 2) thermal pre‐treatment between 185 and 400 °C in air, H2 or Ar atmospheres. The electrochemical reactivity of Pt nanoparticles is acutely affected by the presence of surface organic impurities, making this material ideal for monitoring the effectiveness of OA removal. The results showed that thermal treatment in Ar at temperatures above 400 °C provides highly active particles, with reactivity comparable to the benchmark commercial catalyst, Pt/ETEK. The mechanism involved in thermal desorption of OA was also investigated by thermogravimetric analysis coupled to mass spectrometry (TGA‐MS). Oxidation of HCOOH and adsorbed CO in acidic solution were used as test reactions to assess the Pt electrocatalytic activity. The removal of oleylamine from Pt nanostructures, synthesised by “hot injection”, was assessed employing a range of chemical and thermal methods. The acute sensitivity of Pt reactivity to organic species provides an ideal framework for quantifying the effectiveness of the pre‐treatment methods. Surface‐sensitive probes such as H‐adsorption and the oxidations of HCOOH and adsorbed CO were used as electrochemical performance indicators. Annealing in Ar (400 °C) or H2 (300 °C) resulted in highly active surfaces and the thermal desorption mechanism was investigated by thermogravimetric analysis mass spectrometry.