Koslowski, U.I. ; Herrmann, I. ; Bogdanoff, P. ; Barkschat, C. ; Fiechter, S. ; Iwata, N. ; Takahashi, H. ; Nishikori, H.: Evaluation and analysis of PEM-FC performance using non-platinum cathode catalysts based on pyrolysed Fe- and Co-porphyrins - influence of a secondary heat-treatment. ECS Transactions 13 (2008), p. 125-141
10.1149/1.3039771
Abstract:
Porphyrin based catalysts were prepared by the pyrolysis of transition metal-macrocycles in the presence of iron oxalate as foaming-agent and by the addition of sulfur. Characterization was performed using N2 and H2O sorption measurements, XPS, Raman and 57Fe-Mößbauer spectroscopy, RRDE and PEM Fuel Cell experiments. ORR-activity of already pyrolysed material was found to be significantly enhanced by a secondary heat-treatment in either N2, CO2 or NH3. Additionally, the specific surface area was found to increase and in case of NH3, catalytic centers were also generated. The final catalysts exhibit 2-5 wt% metal, 3-6 wt % nitrogen and 1-5 wt% sulfur integrated in an in-situ formed graphene network. However, despite the high efficiency in RDE measurements, in FC tests only 2 % of electrical power compared to a 45 wt% Pt/C catalyst is reached. An unsuitable morphology of the GDE and a high hydrophilicity of the catalyst were identified as limiting factors.