What question did this study set out to answer?

The study aims to assess the performance of porphyrin-based non-platinum catalysts in PEM fuel cells after a secondary heat treatment.

November 17, 2008

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

Key Points

The study aims to assess the performance of porphyrin-based non-platinum catalysts in PEM fuel cells after a secondary heat treatment.
Porphyrin catalysts were prepared through pyrolysis of transition metal-macrocycles with iron oxalate and sulfur.
Characterization involved N2 and H2O sorption, XPS, Raman spectroscopy, and 57Fe-Mößbauer spectroscopy.
PEM fuel cell experiments assessed ORR-activity pre- and post-secondary heat-treatment.
Secondary heat-treatment significantly enhances ORR-activity, increasing specific surface area and generating additional catalytic centers with NH3.
Final catalysts contain 2-5 wt% metal, 3-6 wt% nitrogen, and 1-5 wt% sulfur embedded in a graphene network.
Fuel cell tests show only 2% efficiency compared to 45 wt% Pt/C catalyst, limited by unsuitable morphology and high hydrophilicity.

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.

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