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Graphite nitrogen, pyridine nitrogen and pyrrole nitrogen are the main nitrogen types in nitrogen-doped graphene materials. In order to investigate the mechanism of the oxygen reduction activity of nitrogen-doped graphene, several models of nitrogen-doped graphene with different nitrogen contents and different nitrogen types are developed. The nitrogen content is varied from 1.3 at% to 7.8 at%, and the adsorption energy is calculated according to the established models, then the band gaps are analyzed through the optimization results, so as to compare the magnitude of the conductivity. Finally, the oxygen reduction activity of graphite nitrogen-doped graphene (GNG) is found to be better than pyridine nitrogen-doped graphene (PDNG) and pyrrole nitrogen-doped graphene (PLNG) when the nitrogen content is lower than 2.6 at%, and the oxygen reduction activity of PDNG is the best when the nitrogen content was higher than 2.6 at%.

In this study, Pt-Pd alloy catalyst was fabricated on carbon papers via electro-deposition as an alternative catalyst for oxygen reduction in air-cathode Microbial Fuel Cells (MFCs). Effects of electro-deposition cycles and supporting materials (graphene and carbon nanotubes (CNTs)) on oxygen reduction reaction (ORR) activity of the Pt-Pd electrode and power generation in MFCs were investigated. The structural and electrochemical properties of the Pt-Pd catalyst were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Results showed that the Pt-Pd electrode showed a good ORR activity. A MFC with a Pt-Pd cathode of 15 deposition cycles produced a maximum power density of 1274 mWm −2 , comparable to that with a conventional Pt/C cathode (0.5 mg Pt cm −2 ). CNT as the supporting material further increased ORR activity of the Pt-Pd electrode and power generation capacity in MFCs, while graphene as the supporting material did not produce positive effects. XRD results confirmed the presence of Pt/Pd elements on the electrode. SEM results showed that decoration using CNT reduced Pt-Pd particle size and promoted them even dispersion on the carbon paper. The Pt-Pd electrode attained a comparable performance to the Pt/C electrode when controlling an optimum deposition cycles and using CNT as the supporting materials, which demonstrates the potential of replacing Pt as an oxygen reduction catalyst in MFCs due to high oxygen reduction activity and relatively low cost. [ABSTRACT FROM AUTHOR]

Due to its better corrosion resistance and higher mechanical strength, 3D graphene is considered as a promising support for oxygen reduction reaction (ORR) electrocatalysts. However, the chemical inertness nature of graphene makes it difficult for Pt-based catalysts to anchor on. Compared with the spherical catalyst, although the Pt-based octahedral catalyst possesses higher mass activity (MA), it has fewer active sites per unit mass due to its larger size, which further hinders the application of 3D graphene as the support of Pt-based octahedral catalyst. Herein, we developed a facile and effective one-step hydrothermal method to fabricate nitrogen-doped porous graphene (NPG). The carbon material with an interconnected 3D framework and submicron macropores was then used to support Pt-Ni octahedral nanoparticles (NPs). The nitrogen not only increase the number of defects, but also improves the distribution of Pt-based octahedral catalysts on the graphene. The electrochemical surface areas (ECSA) of Pt-Ni/NPG reaches 5.5 times that before N-doping. Relative to commercial Pt/C (JM), Pt-Ni/NPG exhibits 6.8-fold enhancement in MA for 725.2 mA mg Pt −1 at 0.9 V RHE. Particularly, Pt-Ni/NPG showed only 8.6% loss in MA after 8000 cycles of the accelerated durability test, as compared to a sharp decrease of 56.2% for Pt/C after only 4000 cycles. In the accelerated durability test of carbon support, Pt-Ni/NPG also exhibited good durability relative to Pt-Ni/C. These results indicate that the Pt-based octahedral catalyst supported on NPG is expected to be applied to proton exchange membrane fuel cells (PEMFCs). [Display omitted] [ABSTRACT FROM AUTHOR]