First-Principles Study of the Ligand Substituent Effect on ORR Catalysis by Metallocorroles

Reddy, Samala Nagaprasad; Krishnamurthy, Chethana B.; Grinberg, Ilya

doi:10.1021/acs.jpcc.9b11990

Cited by 26 publications

(22 citation statements)

References 33 publications

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“…The limiting potential ( U lim in V), also referred as working potential ,, (or onset potential , ), was employed to assess catalyst performance. Here, U lim represents the largest free energy change among R3–R7 , and is expressed in eq . …”

Section: Methodsmentioning

confidence: 99%

Graphene-Based Dual-Metal Sites for Oxygen Reduction Reaction: A Theoretical Study

Elangovan

et al. 2021

J. Phys. Chem. C

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Single-atom catalysts have expanded the design paradigm for oxygen reduction reaction (ORR) relying on nonplatinum group metals (non-PGM). Here, density functional theory calculations were performed on a variety of dual-metal active centers, consisting of both PGM (Pt and Pd) and non-PGM (Fe, Co, Ni, and Cu) metals, embedded in a monolayer of graphene and coordinated by six pyridinic nitrogen atoms. The dual-metal site stability, OH ligand effect, and electronic structures relevant to ORR were investigated. The ORR reactivities can be depicted in terms of a volcano diagram divided into multiple potential limiting regimes based on a wide range of ΔG OH* values. In addition to OH removal and free molecular O 2 protonation as the potential-limiting steps, the protonation of adsorbed O 2 and O also emerge as likely potential-limiting steps due to strong O 2 adsorptions at certain dual-metal active sites. Among the systems investigated, Fe−Co(OH) s exhibits the highest activity. Moreover, other PGM-free dual-metal sites such as Fe−Fe(OH), Fe−Cu(OH), and Co−Co(OH) also appear to be competitive and would encourage further explorations for Pt-free ORR electrocatalyst alternatives.

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Section: Methodsmentioning

confidence: 99%

Graphene-Based Dual-Metal Sites for Oxygen Reduction Reaction: A Theoretical Study

Elangovan

et al. 2021

J. Phys. Chem. C

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“…Many of the current catalysts used in energy conversion and storage processes are precious Pt‐group metals (PGM), and their high cost and scarcity severely restrict the use of renewable energy technologies [1,2] . This has motivated research into alternative energy conversion catalysts such as non‐precious metal catalysts, single‐atom catalysts and metal‐free catalysts [3–9] …”

Section: Introductionmentioning

confidence: 99%

Origin of the Rarely Reported High Performance of Mn‐doped Carbon‐based Oxygen Reduction Catalysts

Samala

Grinberg

2022

ChemSusChem

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Recent efforts to develop durable high‐performance platinum‐group metal (PGM)‐free oxygen reduction reaction (ORR) electrocatalysts have focused on Fe‐ and Co‐based molecular and pyrolyzed catalysts. While Mn‐based catalysts have advantages of lower toxicity and higher durability, their activity has been generally poor. Nevertheless, several examples of high‐performance Mn‐based catalysts have been reported. Thus, it is necessary to understand why Mn‐based materials much more rarely show high catalytic ORR performance and to determine the factors that can lead to the achievement of such high performance in these rare cases. We have studied the effects of the changes in the macrocycle structure, axial ligand, distance between the active sites, interactions with the dopant N atoms and the presence of an extended carbon network on the ORR catalysis of various Mn‐, Fe‐, and Co‐based systems through the comparison of the adsorption energies of the ORR intermediates. We find that the sensitivity to the local environment changes is the largest for Mn and is the smallest for Co, with Fe between Mn and Co. Our results showed that the strong binding of OH by Mn and the strong sensitivity of the Mn to the modification of its environment necessitate a precise combination of local environment changes to achieve a high onset potential (Vonset) in Mn‐based catalysts. By contrast, the weaker binding of OH by Fe and Co and their weaker sensitivity to local environment changes lead to a wide variety of local environments with favorable catalytic activity (Vonset>0.7 V) for Co‐ and Fe‐based systems. This explains the scarcity of reported Mn‐based pyrolyzed catalysts and suggests that precise material synthesis and engineering of the active site can achieve high‐performance Mn‐based ORR electrocatalysts with high activity and durability.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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In the search for replacement of the platinum‐based catalysts for fuel cells, MN4 molecular catalysts based on abundant transition metals play a crucial role in modeling and investigation of the influence of the environment near the active site in platinum‐group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts. To understand how the ORR activity of molecular catalysts can be controlled by the active site structure through modification by the pH and substituent functional groups, the change of the ORR onset potential and the electron number in a broad pH range was examined for three different metallocorroles. Experiments revealed a switch between two different ORR mechanisms and a change from 2e− to 4e− pathway in the pH range of 3.5‐6. This phenomenon was shown by density functional theory (DFT) calculations to be related to the protonation of the nitrogen atoms and carboxylic acid groups on the corroles indicated by the pKa values of the protonation sites in the vicinity of the ORR active sites. Control of the electron‐withdrawing nature of these groups characterized by the pKa values could switch the ORR from the H+ to e− rate‐determining step mechanisms and from 2e− to 4e− ORR pathways and also controlled the durability of the corrole catalysts. The results suggest that protonation of the nitrogen atoms plays a vital role in both the ORR activity and durability for these materials and that pKa of the N atoms at the active sites can be used as a descriptor for the design of high‐performance, durable PGM‐free catalysts.

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First-Principles Study of the Ligand Substituent Effect on ORR Catalysis by Metallocorroles

Cited by 26 publications

References 33 publications

Graphene-Based Dual-Metal Sites for Oxygen Reduction Reaction: A Theoretical Study

Graphene-Based Dual-Metal Sites for Oxygen Reduction Reaction: A Theoretical Study

Origin of the Rarely Reported High Performance of Mn‐doped Carbon‐based Oxygen Reduction Catalysts

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

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