Graphene\nQuantum-Dot-Supported Platinum Nanoparticles:\nDefect-Mediated Electrocatalytic Activity in Oxygen Reduction

Abstract

Graphene quantum dot (GQD)-supported\nplatinum (Pt/G) nanoparticles\nwere prepared by a simple hydrothermal procedure at controlled temperatures.\nTransmission electron microscopic measurements showed that the platinum\nnanoparticles exhibited a rather consistent core size within the narrow\nrange of 2.5–3.5 nm in diameter (average core diameters slightly\nlower than 3.0 nm) when the hydrothermal temperatures were varied\nbetween 140 and 180 °C, whereas at higher temperatures (200 °C)\nthe nanoparticle core size was markedly larger, as a result of weakened\nanchoring and passivation of the metal nanoparticles by the diminishment\nof the GQD structural defects. Spectroscopic measurements based on\nFourier-transformed infrared, Raman, and X-ray photoelectron spectroscopies\nconfirmed the formation of various oxygenated structural defects on\nGQDs and the variation of their concentrations with the hydrothermal\nconditions. Interestingly, electrochemical studies showed that the\nelectrocatalytic activity of the series exhibited a volcano-shaped\nvariation with the GQD structural defects, with the best identified\nas the samples prepared at 160 °C for 12 h and at 180 °C\nfor 6 h where the mass activity was found to meet the DOE target for\n2017. This remarkable performance was accounted for by the deliberate\nmanipulation of the adsorption of oxygen and reaction intermediates\non platinum by the GQD structural defects through partial charge transfer.\nThe strategy presented herein may offer a new paradigm in the design\nand engineering of nanoparticle catalysts for fuel cell electrochemistry.