Electrochemical Catalytic Activity for Oxygen Reduction Reaction of Nitrogen-Doped Carbon Nanofibers

Abstract

The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer.

Low-temperature growth of nitrogen-doped carbon nanofibers by acetonitrile catalytic CVD using Ni-based catalysts

“…Furthermore, each product had a single DTA exothermic peak at approximately 440°C, suggesting that the contents of amorphous carbon deposits in the products were very low. The nitrogen content of products obtained at 400°C using the N-O, N-R, and N-I catalysts were 3.6, 3.8, and 3.2 at.%, respectively, which were typical values in CCVD using acetonitrile (Kim et al 2011). Therefore, we confirmed that our catalysts can effectively yield a relatively large amount of N-CNFs even though they contain a small amount of Ni species as the catalytic component.…”

“…Figure 2 depicts the SEM images of products obtained at 400°C using the N-O, N-R, and N-I catalysts. Regardless of the calcination atmosphere, the N-CNFs with a fiber diameter of several tens of nanometers were obtained, indicating that their morphologies were similar to those of N-CNFs synthesized by a conventional process (Kim et al 2011). As shown in Fig.…”

“…In contrast, the nitrogen content increased monotonically with increasing temperature. The temperature dependence of growth rate and nitrogen content is typical, and the possible mechanism can be explained based on the different diffusion rates over the catalysts of carbon species and nitrogen species, which were formed via the thermal decomposition of acetonitrile (Kim et al 2011). Due to a lower diffusion rate of nitrogen species compared with that of carbon species at low temperatures, the deposition of carbon species on the catalysts was larger than that of nitrogen species.…”

“…To overcome such drawbacks, high-efficiency production of N-CNFs at low temperatures is required. Lim and co-workers synthesized N-CNFs at low temperatures less than 500°C using a magnesium oxide-supported nickel-iron catalyst; however, the growth rates were relatively low (Kim et al 2011;Lim et al 2009). To the best of our knowledge, there is no study focusing on low-temperature growth of N-CNFs.…”

Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

“…Kim et al [68] studied nitrogen-doped carbon nanofibers in an acidic DMFC cathode and could generate moderate electrical current. Sun et al [69] co-doped cheap carbon black materials with nitrogen and fluorine and used them as ORR catalysts in a direct methanol AAMFC.…”