Supercatalysis by Superexchange

Fletcher, Stephen; Dijk, Nicholas J. Van

doi:10.1021/acs.jpcc.6b09099

Cited by 13 publications

(7 citation statements)

References 66 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Electron transfer reactions use the empty orbitals of the conduction band 1,2 for enhanced electron transport, as described in previous studies. 30,31 This is nontrivial, however, because an underestimation (or even neglection) of the QEXI term in calculations will lead to an inevitable overestimation of the E gap band and to an exponential overestimation of the activation energy (e −E gap band /k B T ).…”

Section: Introductionmentioning

confidence: 99%

Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange

Biz

Fianchini²,

Gracia³

2021

ACS Catal.

View full text Add to dashboard Cite

The understanding of quantum correlations within catalysts is an active and advanced research field, absolutely necessary when attempting to describe all the relevant electronic factors in catalysis. In our previous research, we came to the conclusion that the most promising electronic interactions to improve the optimization of technological applications based on magnetic materials are quantum spin exchange interactions (QSEI), nonclassical orbital mechanisms that considerably reduce the Coulomb repulsion between electrons with the same spin. QSEI can stabilize open-shell orbital configurations with unpaired electrons in magnetic compositions. These indirect spin-potentials significantly influence and differentiate the catalytic properties of magnetic materials. As a rule of thumb, reaction kinetics (thus catalytic activity) generally increase when interatomic ferromagnetic (FM) interactions are dominant, while it sensibly decreases when antiferromagnetic (AFM) interactions prevail. The influence of magnetic patterns and spin-potentials can be easily spotted in several reactions, including the most important biocatalytic reactions like photosynthesis, for instance. Moreover, we add here the concept of quantum excitation interactions (QEXI) as a crucial factor to establish the band gap in materials and as a key factor to efficiently mediate electron transfer reactions. In the present Perspective, we offer a general conceptual overview, mainly based on our recent research, on the importance of strongly correlated electrons and their interactions during catalytic events. We present the physical principles and meanings behind quantum exchange in a way that facilitates a comprehensive understanding of the electronic interactions in catalysis from their quantum roots; we explore the issue via mathematical treatment as well as via intuitive visual space/time diagrams to expand the potential readership beyond the domain of physicists and quantum chemists.

show abstract

Section: Introductionmentioning

confidence: 99%

Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange

Biz

Fianchini²,

Gracia³

2021

ACS Catal.

View full text Add to dashboard Cite

show abstract

“…Among the MPc@MCN materials, FePc@MCN and CoPc@MCN exhibit high positive onset potentials in both acidic and basic media (Supporting Information Table S3). The high catalytic efficiency of FePc and CoPc is previously hinted by Fletcher et al The highest activity of FePc@MCN for the ORR over the other materials (including CoPc@MCN) may be attributed to the nature of bonding of oxygen with the Fe in FePc …”

Section: Resultsmentioning

confidence: 70%

Metal (Mn, Fe, Co, Ni, Cu, and Zn) Phthalocyanine-Immobilized Mesoporous Carbon Nitride Materials as Durable Electrode Modifiers for the Oxygen Reduction Reaction

et al. 2020

View full text Add to dashboard Cite

In the search for alternative sources to replace fossil fuels, carbon nitride materials can be used in a variety of ways. In the present work, porosity is introduced to the carbon nitride material using mesoporous silica material, MCM-41, as a hard template, and a mesoporous carbon nitride (MCN) material is synthesized. Further, the MCN is modified by immobilizing metal phthalocyanine (MPc, where M = Mn, Fe, Co, Ni, Cu, and Zn). The resulting MPc-incorporated MCN materials (MPc@MCN) were tested for the electrocatalytic oxygen reduction reaction (ORR) in acidic and basic media. Detailed studies reveal that the FePc@MCN and CoPc@MCN materials exhibit higher ORR activity than the other composites in 0.1 M KOH. FePc@MCN follows a direct four-electron oxygen reduction mechanism and shows ORR onset potential (vs RHE) at 0.93 V (in 0.1 M KOH), which is very close to the onset potential exhibited by the state-of-the-art material, Pt-C (1.0 V), and higher than several similar composites of MPc with carbon supports tested in similar environments. Besides, due to the inherent property of coordination through nitrogen present on the MCN, FePc@MCN shows excellent stability even after 3000 cyclic voltammetry (CV) cycles. FePc@MCN was found to have a better methanol tolerance in comparison to Pt-C in basic medium. CoPc@MCN shows a highly selective two-electron reduction reaction in both acidic and basic media at lower overpotential than many of the reported catalysts for the two-electron oxygen reduction. Therefore, these materials (FePc@MCN and CoPc@MCN) can be used as suitable alternatives to replace Pt and other expensive materials in ORR and related applications.

show abstract

“…Initially, ORR always involves the transfer of an itinerant electron from the catalyst with its spin antiparallel to the initial triplet state of the ↓O=O↓ molecule to match the Pauli exclusion principle. In this situation of strong electronic coupling of the initial and final valence states, we use equation Equation (1), comparable to other approaches mainly developed by Gerischer, or Marcus, to evaluate the rate coefficient,

{K ((), T)}_{S T S T}^{-}

, of heterogeneous electron‐transfer reactions. A new term

E_{T . S . B a n d . G a p}^{S P I N}

is defined as the energy required to place an electron with the appropriate spin orientation in the conduction band of the catalyst able to form the transition state (T.S.).…”

Section: Resultsmentioning

confidence: 99%

Analysis of the Magnetic Entropy in Oxygen Reduction Reactions Catalysed by Manganite Perovskites

Gracia¹,

Munárriz

Polo

et al. 2017

ChemCatChem

View full text Add to dashboard Cite

Manganese oxides with a half‐metallic ground state are particularly active for oxygen reduction reactions (ORR). La0.67Sr0.33MnO3 (LSMO) perovskite is the archetypal example for compositions with a Curie temperature (TC) above room temperature and with a high intrinsic activity for the partial reduction of triplet‐state O2. The ferromagnetic (FM) character of the superexchange interactions in LSMO facilitates both charge and spin transport below 370 K. Other than the enhanced electronic conductivity, the reduced spin entropy seems to be relevant in oxygen catalysis because the magnetic ordering extends to the surface. The sign of the exchange interactions determines the adsorption of the triplet oxygen molecule with its spin antiparallel to the FM catalysts. Based on the transition‐state theory, we report that on LSMO, the hindrance resulting from the magnetic entropy for the initial reduction of O2 by two antiparallel electrons to diamagnetic intermediates (such H2O2) is minimum. On the other hand, the additional reduction of H2O2 to H2O, diamagnetic steps, prefers paramagnetic catalysts with higher magnetic entropy such as La0.4Sr0.6MnO3 to avoid spin accumulation.

show abstract

Supercatalysis by Superexchange

Cited by 13 publications

References 66 publications

Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange

Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange

Metal (Mn, Fe, Co, Ni, Cu, and Zn) Phthalocyanine-Immobilized Mesoporous Carbon Nitride Materials as Durable Electrode Modifiers for the Oxygen Reduction Reaction

Analysis of the Magnetic Entropy in Oxygen Reduction Reactions Catalysed by Manganite Perovskites

Contact Info

Product

Resources

About