Fe-N/C type ORR catalysts were synthesized using FeSO4∙7H2O as the Fe precursor, nitrogen containing organic compounds as N precursors and carbide derived carbon as the carbon support. To synthesize catalysts, precursors and carbon support were mixed into a slurry, dried and pyrolyzed at 800 °C in Ar for 1.5 h [4]. Nitrogen containing organic compounds were following: urea (Urea), ethylenediaminetetraacetic acid disodium salt (EDTA), 1,3-di(1H-imidazol-1-yl)-2-propanol (DIPO), 1,10-phenanthroline (Phen) and 2,2’-bipyridine (Bipyr). Silicon, molybdenum, titanium carbide derived carbons as the carbon supports were compared.
Prepared catalysts were characterized by several physical characterization methods: the nitrogen sorption method, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, transmission electrode microscopy, scanning electron microscopy, time of flight secondary ion mass-spectrometry and Raman spectroscopy.
The electrocatalytic activity of the various catalysts was investigated in O2 saturated in 0.1M KOH and 0.1M HClO4 solutions using rotating disc electrode method. Additionally, durability of the catalysts was tested during ~150 h in both acid and alkaline solutions. For the durability test, the electrode was cycled within the potential range of 0.21 – 1.23 V vs RHE in Ar saturated solution.
The ORR activity of studied catalysts in both acid and alkaline solution strongly depends on the N precursor used. The half-wave potential E1/2 value for studied catalysts increases in the following order: C < Fe-Urea/C < Fe-EDTA/C < Fe-DIPO/C £ Fe-Phen/C £ Fe-Bipyr/C.
In acidic conditions the potential degradation rate is faster than in alkaline conditions for all studied catalysts. The fact that both catalysts showed better durability in alkaline conditions can be explained by possible dissolution of active particles or protonation of ORR active centers at low pH [2,5].
Acknowledgements: This work was supported by the projects TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), NAMUR ”Nanomaterials - research and applications” (3.2.0304.12-0397) and by the Estonian institutional research grant No. IUT20-13.
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