Evidence of carbon-supported porphyrins pyrolyzed for the oxygen reduction reaction keeping integrity

Abstract

Fe(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (FeTPP) and Co(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (CoTPP) were adsorbed on carbon Vulcan and studied as electrocatalysts for the oxygen reduction reaction (ORR) before and after pyrolysis. The pyrolysis process was also simulated through ab initio molecular dynamic simulations and the minimum energy path for the O2 dissociation after the interaction with the metal center of the FeTPP and CoTPP were calculated. After the pyrolysis the FeTPP showed the best performances reducing O2 completely to H2O with increased limiting current and lower overpotential. Tafel slops for the various catalysts did not change after the pyrolytic process suggesting that the mechanism for the ORR is not affected by the heat treatment. TEM images, X-ray diffraction, XPS spectroscopy, 57Fe Mössbauer, and DFT simulations, suggest that there is no breakdown of the macrocyclic complex at elevated temperatures, and that the macro cyclic geometry is preserved. Small variations in the Metal-O2 (M-O2) binding energies and the M–N bond length were observed which is attributed to the dispersive interaction between the macrocycles and the irregular surface of the Vulcan substrate induced by the heat treatment and causing better interaction with the O2 molecule. The theoretical strategy herein applied well simulate and explain the nature of the M–N–C active sites and the performances towards the ORR.

Pyrolyzed cobalt hexacyanocobaltate dispersed on reduced-graphene-oxide as an electrocatalyst of the oxygen reduction reaction in an alkaline medium

“…These properties support our current strategy of producing enhanced electrocatalysts for oxygen reduction based on pyrolysis of metal hexacyanometallates composited with rGO. On mechanistic grounds, it is reasonable to expect that, as reported earlier for various pyrolyzed N-coordinated cobalt or iron systems, 89,93,107,108 the adsorption of O 2 on Co( ii ) precedes fast transfer of the first electron. Further research to confirm the potential utility of these materials as catalysts in fuel cells will be expanded, especially factors involving long term stability.…”

“…It is noteworthy that the existence of MN y (where M is Co or Fe) previously has been postulated for the various N-coordinated systems after pyrolysis. 88–93…”

“…It is noteworthy that the existence of MN y (where M is Co or Fe) previously has been postulated for the various N-coordinated systems aer pyrolysis. [88][89][90][91][92][93] Electrocatalysis of the oxygen reduction reaction Electrochemical studies conrm that pyrolysis is a practical method for preparation of a material, NCoC@rGO, for electrocatalysis of the ORR. Fig.…”

Mono-, bi- and tri-metallic platinum group metal-free electrocatalysts for hydrogen evolution reaction following a facile synthetic route

“…This instability might be due to the fact that the Pc rings remained on the surface of the underlying carbon structure, and were not embedded into the carbon skeleton. 77…”

2,6-Diaminopyridine-Based Polyurea as an ORR Electrocatalyst of an Anion Exchange Membrane Fuel Cell

“…Another option is to use a macrocyclic compound [ 10 , 11 , 12 , 13 , 14 , 15 ] to capture metal ions by nitrogen, i.e., N MOFs. Two major N-macrocyclic compounds used to prepare MOFs and M–Nx–Cs are porphyrin [ 16 , 17 , 18 , 19 , 20 , 21 ] and phthalocyanine [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Both use four -Ns to complex with the central metal and can create an M–N4–C structure after calcination.…”