Effective exposure of nitrogen heteroatoms in 3D porous graphene framework for oxygen reduction reaction and lithium–sulfur batteries

The introduction of nitrogen heteroatoms into carbon materials is a facile and efficient strategy to regulate their reactivities and facilitate their potential applications in energy conversion and storage. However,most of nitrogen heteroatoms are doped into the bulk phase of carbon without site selectivity, which significantly reduces the contacts of feedstocks with the active dopants in a conductive scaffold. Herein we proposed the chemical vapor deposition of a nitrogen-doped graphene skin on the 3D porous graphene framework and donated the carbon/carbon composite as surface N-doped grapheme（SNG）. In contrast with routine N-doped graphene framework（NGF） with bulk distribution of N heteroatoms, the SNG renders a high surface N content of 1.81 at%, enhanced electrical conductivity of 31 S cm^（-1）, a large surface area of 1531 m^2 g^（-1）, a low defect density with a low I_D/I_G ratio of 1.55 calculated from Raman spectrum, and a high oxidation peak of 532.7 ℃ in oxygen atmosphere. The selective distribution of N heteroatoms on the surface of SNG affords the effective exposure of active sites at the interfaces of the electrode/electrolyte, so that more N heteroatoms are able to contact with oxygen feedstocks in oxygen reduction reaction or serve as polysulfide anchoring sites to retard the shuttle of polysulfides in a lithium–sulfur battery. This work opens a fresh viewpoint on the manipulation of active site distribution in a conductive scaffolds for multi-electron redox reaction based energy conversion and storage.

Effect of Oxygen Plasma on Low Dielectric Constant HSQ (Hydrogensilsesquioxane) Films

The commercially available hydrogensilsesquioxane （HSQ） offers a low dielectric constant. In this paper, the impact of oxygen plasma treatment has been investigated on the low- k HSQ films. Fourier transform infrared （FTIR） spectroscopy was used to identify the network structure and cage structure of Si-O-Si bonds and other possible bonds after treatments. C-V and I-V measurements were used to determine the dielectric constant, the electronic resistivity and the breakdown electric field, respectively. The result indicates that oxygen plasma treatment will damage the HSQ films by removing the hydrogen content. Both dielectric constant and leakage current density increase significantly after oxygen plasma exposure. The dielectric constant and leakage current density can both be decreased by annealing at 350 ℃ for 1.5 h in nitrogen ambient. The reason is that the open porous of the external films can be modified and density of thin film be increased. The rough surface can be smoothed.