Poisoning the Oxygen Reduction Reaction on Carbon-Supported Fe and Cu Electrocatalysts: Evidence for Metal-Centered Activity

Abstract

Whether or not the active sites for the oxygen reduction reaction (ORR) in electrocatalysts based on carbon-supported transition-metal complexes are metal-centered has become controversial, especially for heat-treated materials. Some have proposed that the transition metal only serves to form highly active sites based on nitrogen and carbon. Here, we examine the oxygen reduction activity of carbon-supported iron(II) phthalocyanine (FePc) before and after pyrolysis at 800 °C and a carbon-supported copper(II) complex with 3,5-diamino-1,2,4-triazole (CuDAT) in the presence of several anions and small-molecule poisons, including fluoride, azide, thiocyanate, ethanethiol, and cyanide. CuDAT is poisoned in a manner consistent with a Cu-based active site. Although FePc and pyrolyzed FePc are remarkably resilient to most poisons, they are poisoned by cyanide, indicative of Fe-based active sites.

Rational Design and Synthesis of Low-Temperature Fuel Cell Electrocatalysts

“…TEM results in Fig. 8g reveal that the strain in PtPb/Pt nanoplates is anisotropic in which Top-Pt layers were fully coherent to the PtPb core, with an 11% compressive strain along the [01 1 ] Pt and a 7.5% tensile strain along [100] Pt; whereas in the edge-Pt layer, the [001] direction of Pt was fully confined within PtPb, resulting in a 7.5% tensile strain and small compressive strain (1.0%) along [110] Pt. This finding is somewhat analogous to alloying Pt with rare earth metals.…”

“…In studies using surface probing on Fe/N/C catalysts, efforts have been made to apply strong ligands as surface probes, such as CN − developed by Gewirth et al [110] and halide ions and sulphurcontaining species (e.g. SCN − , SO 2 , and H 2 S) by Zhou et al [107], in which strong ligands are added into the electrolyte, coordinating iron centres and hindering oxygen absorption on iron sites to suppress the ORR activity of Fe/N/C catalysts (Fig.…”

Silicon nanograss as micro fuel cell gas diffusion layer

“…There have been speculations that the catalytic activity is a result of metal residues from carbon material synthesis as described in the previous paragraph due to the difficulty of removing all the metal, but recently N-doped carbon materials synthesized without metal catalyst have been shown to be as active [141,151,152]. Moreover, cyanide, which is reported to poison a Fe-C-N catalyst [154], had no effect on the ORR activity of an Ndoped carbon [155].…”

Preparation and mechanism study of non-precious metal catalysts for electrochemical oxygen reduction

“…a, RDE measurements of the ORR activity of carbon-supported CuDAT in O2-saturated pH 6 phosphate buffer alone (black) and containing 10 mM poisons (left). RDE measurements of the ORR activity of carbonsupported FePc (blue lines) and pyrolyzed carbon supported FePc (red lines) in O2-saturated 0.1 M NaOH alone (solid lines) and containing 10 mM KCN, [79] with permission from American Chemical Society.…”

“…They found the Cu-NC can be poisoned by fluoride, azide, thiocyanate, ethanethiol, and cyanide while Fe-NC can only be poisoned by cyanide ( figure 12). [79] Chen used the same CN -method the determine that the Fe in Fe-N4 motif is the active site. [76] As we've mentioned in the DFT part, TM embedded in graphitic structure may also contribute to ORR.…”