Influence of Nitrogen‐Containing Precursors on the Electrocatalytic Activity of Heat‐Treated Fe ( OH ) 2 on Carbon Black for O 2 Reduction

Abstract

Ferrous hydroxide gel was adsorbed on carbon black to produce /C. Various N‐containing precursors were then either adsorbed on this material before pyrolysis at 1000°C in Ar or introduced as vapors in the reactor during the pyrolysis step. The N‐containing precursors adsorbed on /C were either polyacrylonitrile (PAN), tetracyanoquinodimethane (TCNQ), or metal‐free phthalocyanine , while the N‐containing vapors injected into the reactor were acetonitrile or ammonia . The resulting materials were characterized by X‐ray diffraction analysis, transmission electron microscopy, and X‐ray photoelectron spectroscopy. Their electrochemical activities for reduction were determined using a rotating disk electrode in ‐saturated at pH 0.5. Upon heating, /C is mostly transformed into iron carbide aggregates. Adding a N‐containing species during the pyrolysis of /C is essential for obtaining catalytic activity of reduction. However, all N‐containing precursors are not equivalent. The catalytic activity increases along the series: PAN < TCNQ < . This series also represents an increasing polarizability of the N‐containing precursor. The effect of and vapors are equivalent, yielding slightly higher electroactivities than those obtained with adsorbed PAN. All N‐containing precursors generate pyrolysis products containing C and N atoms. This is also true for vapors since reacts with the carbon support at 1000°C. Deconvolution of the core level spectra of the catalytic materials leads to the identification of three separate contributions assigned to pyridinic, pyrrolic, and graphitic‐type nitrogens. It is demonstrated that none of these N‐type contributions alone seem to be responsible for the catalytic activity.