Structural and Physical Parameters Controlling the Oxygen Reduction Reaction Selectivity with Carboxylic Acid-Substituted Cobalt Corroles Incorporated in a Porous Carbon Support

Abstract

Three cobalt(III) complexes of regioisomeric trans-A 2 B-corroles were designed and efficiently synthesized. The corroles were adsorbed on smooth glassy carbon (GC) and black pearls 2000 (BP2000), high-surface-area carbon. Albeit spatially separated from the cobalt reaction center, the position of COOH group has a profound influence on the oxygen reduction reaction electrocatalytic reactivity when on GC, whereas on BP2000, a significant increase in selectivity toward the 4-electron reduction was observed in an alkaline environment. This is attributed to the wetting properties of the hydrophobic pores of BP2000, which considerably lower the dielectric constant in the pore water environment, stabilize the charged OOH − intermediate, and favor the 4-electron reduction pathway with the cobalt-bis-pentafluorophenyl (phenyl-para-carboxylic acid), when compared to analogous corroles with the COOH group at the ortho-and meta-positions.

Control of Molecular Catalysts for Oxygen Reduction by Variation of pH and Functional Groups

“…Cobalt 10‐(2‐carboxyphenyl)‐5,15‐bis‐(pentafluorophenyl) corrole ( ortho ‐Corrole ) and cobalt 10‐(4‐carboxyphenyl)‐5,15‐bis‐(pentafluorophenyl) corrole ( para ‐Corrole ) were synthesized as described elsewhere (Figure 1). [22] Cobalt(III)‐5,10,15‐tris‐(trifluoromethyl) corrole ( CF 3 ‐Corrole ) was synthesized according to previously published method [18] . All chemicals were AR grade.…”

“…In the past few years, we have investigated the catalytic activity of metallo‐corroles towards ORR in acidic and alkaline media [14–21] . In these studies, different metal centers and substituents were introduced to the corroles ring.…”

Corroles at work: a small macrocycle for great applications

“…This result evidenced the importance of the corrole dimensions on the ORR catalytic activity and led the researchers to [45][46][47] look to novel corrole-bearing substituents that can influence both the electronic and size-related properties of catalysts. In particular, the -CF 3 group as the meso-substituent attracted some attention because it is a small and strong electronwithdrawing substituent, two features that are particularly promising for the target application.…”

“…12a and b) has been studied. 45 The rationale of the substitution was to investigate the possible interaction of the carboxylic group with the Co ion in the O 2 coordination, driving the ORR to the desired 4-e À pathway. Also, in this case, the experiments were carried out in alkaline and in acidic solutions, using GC and BP2000 electrodes.…”

Enzyme‐Inspired Iron Porphyrins for Improved Electrocatalytic Oxygen Reduction and Evolution Reactions

“…Comparison with previously reported molecular catalysts under similar conditions also demonstrates the high ORR activity of 1/CNT. [23,25,29,[55][56][57][58][59] Note that unmodified CNTs have very poor electrocatalytic ORR activity (Figure 3 a).…”