Active Non-Platinum Cathode Catalysts for Direct-Methanol Alkaline Fuel Cells

The development of novel catalyst materials for oxygen reduction reaction (ORR) is one of the key topics in fuel cell research. In order to replace expensive noble-metal based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been investigated. An attractive approach is to employ nitrogen-containing carbon nanomaterials for this purpose ^1-3.

   In this work the electrochemical reduction of oxygen has been studied on nitrogen-doped carbon nanomaterials modified glassy carbon (GC) electrodes. N-doped carbon nanotubes (N-CNT) and N-doped few-layer graphene/carbon nanotube (N-FLG/CNT) composite materials were investigated as catalyst materials. Dicyandiamide (DCDA) was used as nitrogen precursor for nitrogen doping of carbon nanomaterials. The doping was achieved by pyrolysing nanocarbon materials in the presence of DCDA at 800 °C. The CNT or FLG/CNT-to-nitrogen precursor mass ratio was 1:20. Electrochemical experiments were carried out in 0.1 M KOH using the rotating disk electrode (RDE) method. GC electrodes were modified using carbon nanomaterial suspension in isopropanol in the presence of Fuma-Tech FAA3 ionomer. The fuel cell performance of N-doped carbon materials was investigated by fabricating membrane-electrode assemblies (MEAs) using Fuma-Tech FAA3 membrane and for comparison purposes a commercial Pt/C catalyst was used as cathode material.

  The RDE experiments showed extraordinary electrocatalytic activity of N-doped carbon nanomaterials toward the ORR in alkaline media.  A comparative study of direct methanol alkaline fuel cell performance was also performed. The power density curves are presented in Fig. 1. The MEAs with N-CNT, N-FLG/CNT and commercial 60% Pt/C cathode catalysts had power densities of 0.92, 0.72 and 0.72 mW cm⁻² respectively, using methanol as fuel on anode side and pure O₂ gas on cathode side. The results obtained in this work show that N-FLG/CNT and N-CNT catalysts possess excellent ORR activity in alkaline media and could be used as alternative cathode catalysts in alkaline anion-exchange membrane fuel cells.

References

1. I. Kruusenberg, S. Ratso,  M. Vikkisk, P. Kanninen, T. Kallio, A.M. Kannan, K. Tammeveski, J. Power Sources, 281, 94, 2015.

2. M. Vikkisk, I. Kruusenberg, U. Joost, E. Shulga, I. Kink, and K. Tammeveski, Appl. Catal. B: Environ., 147, 369, 2014.

3. S. Ratso, I. Kruusenberg, M. Vikkisk, U. Joost, E. Shulga, I. Kink, T. Kallio, and K. Tammeveski, Carbon, 73, 361, 2014.