Characteristics of Nitrogen and Boron Co-Doped Graphene Nanosheets Synthesized By Simple Microwave-Hydrothermal Method

Graphene nanosheets have received much attention in electrochemical energy research areas because of its remarkable properties such as high specific surface area and electrical conductivity. The properties satisfy various requirements for electrochemical device’s electrode. In that application, the enhancement of the oxygen reduction reaction (ORR) activity has been considered as one of the important issues. For enhancing ORR activity, various precious metal catalysts have been investigated in spite of their high prices. In recent years, research efforts have been focused on developing various non-metal catalysts for overcoming the disadvantage of metal catalysts.

                  Most of carbon-based non-metal catalysts were synthesized via expensive method such as chemical vapor deposition (CVD) method. The method is not suitable for mass production method. In this study, we synthesized nitrogen and boron co-doped graphene nanosheets (BNG) from graphene oxide (GO) by simple microwave-hydrothermal method. The synthesis time can be significantly reduced result from assistance of microwave heating. The synthesis process includes doping and reduction process. The samples were prepared under different reduction temperature conditions. For observing the morphology of samples, we carried out scanning electron microscopy (SEM). From Raman spectra analysis, we confirmed that intensity ratio (I_D/I_G) increased with reduction temperature. And we investigated chemical composition and bonding configuration of the BNG samples by X-ray photoelectron spectroscopy (XPS). The results of XPS analysis demonstrated that co-doping and reduction process are successfully achieved. Catalytic activities were characterized by three-electrode system. Linear sweep voltammetry (LSV) was measured in 0.1M KOH electrolyte purged oxygen gas over 1 h, with a 1500 rpm electrode rotation speed and a 10 mVs^-1 scan rate. The LSV results revealed that co-doped samples show higher ORR activity compared to that of non-doped sample and the activity is enhanced with reduction temperature.

 

Acknowledgement

This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (NIPA-2014-H0201-14-1002) supervised by the NIPA(National IT Industry Promotion Agency)