Skip to Content
Merck
  • A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts.

A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts.

Nature communications (2020-10-21)
Travis Marshall-Roth, Nicole J Libretto, Alexandra T Wrobel, Kevin J Anderton, Michael L Pegis, Nathan D Ricke, Troy Van Voorhis, Jeffrey T Miller, Yogesh Surendranath
ABSTRACT

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen2N2)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen2N2)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen2N2)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen2N2)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
1,10-Phenanthroline, ≥99%
Sigma-Aldrich
1,2-Dicyanobenzene, 98%
Sigma-Aldrich
tert-Butanol, ≥99% (GC)
Sigma-Aldrich
Potassium sulfate, 99.99% trace metals basis