Stabilization of Ultrasmall Platinum Nanoparticles by Nitrogen-Doped Carbon: Implications for Catalysis and Electrocatalysis

Abstract

Heterogeneous materials comprising platinum nanoparticles on carbon supports have numerous applications including fuel cell electrodes and heterogeneous catalysts. The effective application of these materials for fuel cells and catalysis will be greatly advanced by the ability to control the oxidation and sintering of the nanoparticles by modifications of the carbon support. One attempt of such control has been doping carbon supports with nitrogen. In this work, a cutting-edge, high-sensitivity, in situ XRD instrument, which allows observation of ultrasmall Pt nanoparticles, has been combined with in situ XPS to provide unprecedented clarity in the characterization of supported Pt nanoparticles in oxidizing and high-temperature environments. On a nitrogen-doped carbon support derived from poly-phenylporphyrin, Pt nanoparticles show increased stability to oxidation and thermal sintering. The enhanced Pt–support interaction arising from the N dopant versus the N-free carbon is manifested by (1) decreased initial Pt particle sizes, (2) small particle size at higher surface densities, (3) increased resistance of Pt nanoparticles to oxidation, (4) increased electron binding energy of Pt0, and (5) increased resistance of Pt nanoparticles to sintering. It is expected that the higher stability of Pt on NC will be manifested in higher activity in fuel cells and high-temperature catalytic reactions.

Benefits of Using Rapid Microwave Heating in the Synthesis of Metal-Free Carbon Electrocatalysts

“…Nitrogen-doped carbons have emerged as promising metal-free electrocatalysts for applications such as oxygen reduction reaction (ORR) in hydrogen fuel cells. − They can also be used as catalyst supports for atomically dispersed metals for various electro- and thermocatalytic processes, as specific doped nitrogen sites act as anchoring sites for metal atoms − and metal nanoparticles. − Nitrogen-doped carbons are commonly synthesized by pyrolyzing a mixture of carbon and nitrogen precursors under an inert atmosphere, typically at temperatures ranging from 600 to 1100 °C. A second method involves introducing oxygen functional groups onto a carbon material using strong acids, followed by heating in NH 3 to incorporate nitrogen species through a reaction with oxygen functional groups. − The heat treatment is crucial in the synthesis of these materials as it impacts the type and concentration of heteroatom dopants, ,, structural defects, , π-electron delocalization and associated Lewis basicity, acid–base properties, , electrical properties, , surface polarity, and porosity of the materials.…”

Selective Hydrogenation of N-Heterocyclic Carboxylate over Nitrogen-Doped Porous Carbon-Supported Nano-Ni

“…In recent years, porous carbon materials have become another ideal metal carrier with excellent properties of high specific surface area, adjustable porosity, thermal stability, chemical stability, etc. N-doped carbon has experienced great development as a catalyst carrier. − For example, Perazzolo et al indirectly proved the increase in the antioxidant capacity of nitrogen-doped materials on Pt nanoparticles by cyclic voltammetry . Nitrogen-doped porous carbon-supported transition metal nanoparticles (NPs), such as Fe and Co, have shown excellent catalytic performance in various reactions. − The introduction of functional groups of N/O can increase the interaction between metal and carrier, effectively stabilize metal ions, and form materials with smaller size distribution and more regular morphology, thus increasing the catalytic activity and reaction stability of nitrogen-doped materials supported on metal. − …”