O₂ Reduction in PEM Fuel Cells: Activity and Active Site Structural Information for Catalysts Obtained by the Pyrolysis at High Temperature of Fe Precursors

Abstract

Catalytic activity for O2 electroreduction in acidic medium has been studied. Catalysts have been produced by pyrolyzing perylene tetracarboxylic dianhydride (PTCDA) combined with Fe and N precursors. The Fe precursors used in this work are either FeII acetate or Cl−FeIII Tetramethoxyphenyl porphyrin (Cl−FeTMPP). The N precursors are NH3 and/or Cl−FeTMPP. To be able to vary the catalytic activity, two synthesis procedures have been used, varying either the heat-treatment temperature or the Fe content of the pyrolyzed materials. All the catalysts have been studied by Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) in order to find out if the relative intensity of one or several secondary ions was following the changes observed in the catalytic activity. Only one ion, FeN2C4 +, may be considered as the signature of the catalytic site generated in this work. It has been detected in all prepared catalysts, whatever the Fe precursor or the synthesis procedure was used. It is proposed that this ion is produced under ToF SIMS analysis from part of a 1,10 phenanthrolinic-type structure, which is itself part of the catalytic site. This catalytic site is probably the same as the one obtained by the pyrolysis at high temperature (≥ 800 °C) of N4−Fe macrocycles adsorbed on carbon black. RDE and PEM fuel cell tests demonstrate that the most performing catalysts are those containing 2 wt % Fe as Cl−FeTMPP and 0.2 wt % Fe as Fe acetate. Increasing the Fe content beyond these limits mainly generates catalytically inactive Fe clusters and interferes with the characterization of the high-temperature active site.

Iron and Nitrogen containing Carbon Catalysts with Enhanced Activity for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

“…Oxygen saturated 0.5 M H 2 SO 4 was used as the electrolyte. The working electrode fabricated with Fe-based catalysts was as follows [19,20,29,30]. 16 mg of the catalyst, 0.4 ml of H 2 O and 0.4 ml of 5 wt.% Nafion ® (Aldrich) were ultrasonically blended for 10 min.…”

“…Single-cell PEM tests were conducted using a homemade fuel cell test station. Gas diffusion electrodes (GDE) and membrane-electrode assembly (MEA) were fabricated according to the procedure reported in literature [2,23,29]. A commercial 20 wt.% Pt/C (E-TEK) and the prepared Fe-based catalysts were used to fabricate anode and cathode, respectively.…”

“…These results confirmed that the presence of oxygen functionalities (quinone groups) on carbon surface played an important role in formation and dispersion of Fe/N active sites thereby enhanced ORR performance. Electrocatalytic ORR activity observed for the heattreated FeTMPP/C was due to the creation of Fe/N moiety on carbon matrix during the pyrolysis [29,30]. Recently, we have demonstrated the necessity of Fe-N 4 clusters for the facile reduction of dioxygen molecule from density functional theory calculations [61].…”

Study on the Relationship Between Catalytic Activity and C-N Structures of a Nitrogen-contained Non-precious Metal Catalyst for Oxygen Reduction Reaction

“…Currently, two types of structures are widely considered as the active site. One is TM-N 4 or TM-N x structure; [5][6][7][8][9][10] the other is C-N structure, which is formed by replacing carbon atoms with nitrogen atoms in graphene matrix of carbon black. [11][12][13][14] Some carbon atoms in graphene matrix of carbon black can be replaced by nitrogen atoms during TM-N/C catalyst preparation to form several types of C-N structures.…”

A Nitrogen‐Doped Polyaniline Carbon with High Electrocatalytic Activity and Stability for the Oxygen Reduction Reaction in Fuel Cells

“…[5][6][7] Thus, the exploration of nonnoble-metal catalysts with both high performance and durability is of great significance, and recognized as a top priority in providing key technological solutions for the commercialization of fuel cells. Many works have explored non-preciousmetal cathode catalysts, reporting on the use of metal-macrocycle complexes and their pyrolized derivatives, [8][9][10] transitional-metal clusters, [11,12] transitional-metal carbides and nitrides, [13,14] metal oxides, [15,16] the recently reported transitionmetal-carbon-nitrogen composites [17][18][19] and carbon-based catalysts, [20,21] and other strategies. Although much progress has been achieved, there are still challenges regarding both ORR activity and stability.…”