Preparation of nitrogen-doped carbon nanoblocks with high electrocatalytic activity for oxygen reduction reaction in alkaline solution

The oxygen reduction reaction (ORR) is traditionally performed using noble-metals catalysts, e.g. Pt. However, these metal-based catalysts have the drawbacks of high costs, low selectivity, poor stabilities, and detrimental environmental effects. Here, we describe metal-free nitrogen-doped carbon nanoblocks (NCNBs) with high nitrogen contents (4.11%), which have good electrocatalytic properties for ORRs. This material was fabricated using a scalable, one-step process involving the pyrolysis of tris(hydroxymethyl)aminomethane (Tris) at 800 ℃. Rotating ring disk electrode measurements show that the NCNBs give a high electrocatalytic performance and have good stability in ORRs. The onset potential of the catalyst for the ORR is -0.05 V (vs Ag/AgCl), the ORR reduction peak potential is -0.20 V (vs Ag/AgCl), and the electron transfer number is 3.4. The NCNBs showed pronounced electrocatalytic activity, improved long-term stability, and better tolerance of the methanol crossover effect compared with a commercial 20 wt% Pt/C catalyst. The composition and structure of, and nitrogen species in, the NCNBs were investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The pyrolysis of Tris at high temperature increases the number of active nitrogen sites, especially pyridinic nitrogen, which creates a net positive charge on adjacent carbon atoms, and the high positive charge promotes oxygen adsorption and reduction. The results show that NCNBs prepared by pyrolysis of Tris as nitrogen and carbon sources are a promising ORR catalyst for fuel cells.