Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies

TL;DR

This study investigates the electronic structure of carbon-encapsulated nickel nanoparticles using spectroscopic techniques and theoretical calculations, revealing a multilayer graphene shell with defects that protect the metal core from oxidation.

Contribution

It provides detailed spectroscopic and theoretical analysis of the carbon shell structure and its protective role in nickel nanoparticles.

Findings

Carbon shell is multilayer graphene with 6% Stone-Wales defects

Nanoparticles are protected from oxidation for at least two years

Oxidation occurs mainly on the carbon shell after prolonged exposure

Abstract

Electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra are compared with the density of states calculated in the frame of the density functional theory. The carbon shell of Ni nanoparticles has been found to be multilayer graphene with significant (about 6%) amount of Stone--Wales defects. Results of the experiments evidence protection of the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation at least for two years. Exposure in air for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles with coverage of functional groups.