Nonpyrolyzed Fe-N Coordination-Based Iron Triazolate Framework: An Efficient and Stable Electrocatalyst for Oxygen Reduction Reaction.

Pyrolyzed base-metal-based metal-organic frameworks (MOFs) with FeNx coordination are emerging as nonprecious metal catalysts for electrochemical oxygen reduction reaction (ORR). However, surprisingly, nonpyrolyzed MOFs involving Fe-N coordination have not been explored for the ORR. This study concerns the catalytic performance of a semiconducting nonpyrolyzed iron triazolate framework (FeTa2 ) for ORR in alkaline electrolyte. The FeTa2 catalyst is studied as composites with different amounts of conductive Ketjenblack carbon (KB). The performance of these FeTa2 -x KB (x denotes the KB/FeTa2 weight ratio) composites by onset and half-wave potentials of ORR appears to be superior to most previously documented nonpyrolyzed MOFs. Characterization by elemental analysis, FTIR spectroscopy, XPS, and cyclic voltammetry suggest that N-FeIII -OH- sites at the surface of FeTa2 function as the catalytic active sites. This FeTa2 also shows very stable activity during ORR, as supported by accelerated durability test of the FeTa2 -x KB sample (20 000 cycles, ca. 90 h). The framework structure of FeTa2 remains intact during the durability test, which would help to explain its excellent catalytic durability. This would be the first study demonstrating efficient and stable ORR catalysis by a nonpyrolyzed Fe-N coordination-based MOF material.

Is Ammonium Peroxydisulate Indispensable for Preparation of Aniline-Derived Iron-Nitrogen-Carbon Electrocatalysts?

Iron and nitrogen co-doped carbon (Fe-N-C) materials are among the most active non-precious metal catalysts that could replace Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. The synthesis of the Fe-N-C catalysts often involves the use of aniline as the precursor for both N and C and ammonium peroxydisulfate (APS) as an indispensable oxidative initiator for aniline polymerization. Herein, a detailed structure and catalytic ORR performance comparison of aniline-derived Fe-N-C catalysts synthesized with and without the use of APS is reported. The APS-free preparation, which uses Fe(III) ions as the Fe source as well as the aniline polymerization initiator, results in a simple Fe-N-C catalyst with a high activity for the ORR. We show that APS is not necessary for the preparation and even detrimental to the performance of the catalyst.