Resolving the Iron Phthalocyanine Redox Transitions for ORR Catalysis in Aqueous Media

Abstract

Metal macrocycles are among the most important catalytic systems in electrocatalysis and biocatalysis owing to their rich redox chemistry. Precise understanding of the redox behavior of metal macrocycles in operando is essential for fundamental studies and practical applications of this catalytic system. Here we present electrochemical data for the representative iron phthalocyanine (FePc) in both aqueous and nonaqueous media coupled with in situ Raman and X-ray absorption analyses to challenge the traditional notion of the redox transition of FePc at the low potential end in aqueous media by showing that it arises from the redox transition of the ring. Our data unequivocally demonstrate that the electron is shuttled to the Pc ring via the Fe(II)/Fe(I) redox center. The Fe(II)/Fe(I) redox transition of FePc in aqueous media is indiscernible by normal spectroscopic methods owing to the lack of a suitable axial ligand to stabilize the Fe(I) state.

Promoting Li–O2 Batteries With Redox Mediators

“…The complex further reacted to form Li 2 O 2 . Fe(heme) was studied as well, which operates similarly as FePC . These organometallic RMs and some of the RMs mentioned above may also play a role in catalyzing the oxygen evolution reaction (OER), as we will discuss later.…”

“…Some redox mediators, including 2,5‐di‐ tert ‐butyl‐1,4‐benzo‐quinone (DBBQ), Coenzyme Q10 (CoQ 10 ), iron phthalocyanine (FePc), 2‐phenyl‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (PTIO), poly(2,2,6,6‐tetramethylpiperidinyloxy‐4‐yl methacrylate) (PTMA), RuBr 3, and iron protoporphyrin (Fe(heme)), were also studied. These RMs promote the discharge performance in a different way compared to the redox‐shuttle mechanism by forming new complex intermediates to replace LiO 2 .…”

“…On discharge, it operates slightly different to DBBQ and CoQ 10 described above. It binds O 2 first prior to being reduced to the FePC–O 2 − complex . The complex further reacted to form Li 2 O 2 .…”

Comparative Study of the Oxygen Reduction Reaction on Pyrolyzed FePc in Acidic and Alkaline Media

“…The active sites of M/N/C catalysts may consist of both Fe‐N x sites and metal‐free N‐doped carbon. The M−N 4 /M−N 2 centers anchored into the carbon support have been proved catalytically active, and the central metals play a crucial role on the ORR in both acid and alkaline media ,. The transition metals (e. g., Fe or Co) are also supposed to catalyze the carbonization and incorporation of N atom into the carbon matrix, which can tailor the electronic structure of carbon and facilitate the ORR ,.…”

“…The MÀ N 4 /MÀ N 2 centers anchored into the carbon support have been proved catalytically active, and the central metals play a crucial role on the ORR in both acid and alkaline media. [11][12][24][25][26][27][28][29][30][31] The transition metals (e. g., Fe or Co) are also supposed to catalyze the carbonization and incorporation of N atom into the carbon matrix, which can tailor the electronic structure of carbon and facilitate the ORR. [7,[32][33][34] In addition, the nitrogen species can be presented in different forms in M/N/C catalysts including pyridinic-N, pyrrolic-N, and graphitic-N.…”