Three-dimensional Polypyrrole Derived N-doped Carbon Nanotube Aerogel as a High-performance Metal-free Catalyst for Oxygen Reduction Reaction

Graphical 3D N-doped CNT aerogel is facilely synthesized by pyrolysis of the template polymerized PPy, and displays superior ORR activity and stability due to the dominant role of the graphitic-N and the graphitization degree of the carbon materials. A novel N-doped carbon nanotube aerogel has been synthesized by pyrolysis of the three-dimensional tubular polypyrrole networks and evaluated as a metal-free electrocatalyst for the oxygen reduction reaction. The carbon aerogel catalysts are pyrolyzed at 500 °C (PPy/C-500), 700 °C (PPy/C-700), 900 °C (PPy/C-900) and 1050 °C (PPy/C-1050), and display the pyrolyzed temperature-dependent activity and stability. The catalytic activity is increased with the increase of pyrolysis temperature from 500 °C to 1050 °C, ascribed to the high electronically conductive graphitic phases, the thin wall of the three-dimensional tubular carbon aerogel framework and the increased effective active sites. The nitrogen content is reduced with the increase of pyrolysis temperature, and which plays an important role in the stability of the pyrolyzed catalyst. After 1500 cycles, the PPy/C-1050 catalyst shows more positive half-wave potential than the commercial Pt/C catalyst, and displays a quasi-four-electron pathway toward the oxygen reduction reaction in the acid solution. This work provides an effective strategy for preparing the low cost and metal-free N-doped carbon aerogel catalyst from the conjugated conducting polymer, to achieve high activity and stability.