scholarly journals Adiabatic versus non-adiabatic electron transfer at 2D electrode materials

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dan-Qing Liu ◽  
Minkyung Kang ◽  
David Perry ◽  
Chang-Hui Chen ◽  
Geoff West ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Copper Electrode ◽  
Rate Theory ◽  
Multilayer Graphene ◽  
Contact Potential ◽  
Graphene Layers

Abstract2D electrode materials are often deployed on conductive supports for electrochemistry and there is a great need to understand fundamental electrochemical processes in this electrode configuration. Here, an integrated experimental-theoretical approach is used to resolve the key electronic interactions in outer-sphere electron transfer (OS-ET), a cornerstone elementary electrochemical reaction, at graphene as-grown on a copper electrode. Using scanning electrochemical cell microscopy, and co-located structural microscopy, the classical hexaamineruthenium (III/II) couple shows the ET kinetics trend: monolayer > bilayer > multilayer graphene. This trend is rationalized quantitatively through the development of rate theory, using the Schmickler-Newns-Anderson model Hamiltonian for ET, with the explicit incorporation of electrostatic interactions in the double layer, and parameterized using constant potential density functional theory calculations. The ET mechanism is predominantly adiabatic; the addition of subsequent graphene layers increases the contact potential, producing an increase in the effective barrier to ET at the electrode/electrolyte interface.

scholarly journals Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials

2021 ◽  
Author(s):  
Dan-Qing Liu ◽  
Minkyung Kang ◽  
David Perry ◽  
Chang-Hui Chen ◽  
Geoff West ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Electrode Materials ◽  
Copper Substrate ◽  
Experimental Methodology ◽  
Diffusion Limit ◽  
Rate Theory ◽  
Multilayer Graphene ◽  
Contact Potential ◽  
Graphene Layers

<div><div><div><p>Outer-sphere electron transfer (OS-ET) is a cornerstone elementary electrochemical reaction, yet microscopic understanding is largely based on idealized theories, developed in isolation from experiments that themselves are often close to the kinetic (diffusion) limit. Focusing on graphene as-grown on a copper substrate as a model 2D material/metal-supported electrode system, this study resolves the key electronic interactions in OS-ET, and identifies the role of graphene in modulating the electronic properties of the electrode/electrolyte interface. An integrated experimental-theoretical approach combining co-located multi-microscopy, centered on scanning electrochemical cell microscopy (SECCM), with Raman microscopy and field emission-scanning electron microscopy, together with rate theory and density functional theory (DFT) calculations is used to address OS-ET kinetics of hexaamineruthenium (III/II) chloride, [Ru(NH3)6]3+/2+. The experimental methodology allows spatially-resolved electrochemical measurements to be targeted at distinct regions of monolayer, bilayer and multilayer graphene on copper, with high diffusion rates, to reveal ET kinetics in the order: monolayer > bilayer > multilayer. To rationalize these findings we extended the Schmickler-Newns-Anderson model Hamiltonian for electron transfer and parametrized it using constant potential DFT. Combining this model with rate theory reveals that the difference in kinetics at monolayer and bilayer graphene can be rationalized in the context of a dominantly adiabatic mechanism, where the addition of subsequent graphene layers increases the contact potential, producing an increase in the effective barrier to electron transfer. This study provides a roadmap for the integration of experiments, theory, and simulations in order to understand the nature of heterogeneous electron transfer at complex nanostructured electrode materials.</p></div></div></div>

scholarly journals Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials

2021 ◽  
Author(s):  
Dan-Qing Liu ◽  
Minkyung Kang ◽  
David Perry ◽  
Chang-Hui Chen ◽  
Geoff West ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Electrode Materials ◽  
Copper Substrate ◽  
State Theory ◽  
Experimental Methodology ◽  
Diffusion Limit ◽  
Rate Theory ◽  
Multilayer Graphene ◽  
Contact Potential

<div><div><div><p>Outer-sphere electron transfer (OS-ET) is a cornerstone elementary electrochemical reaction, yet microscopic understanding is largely based on idealized theories, developed in isolation from experiments that themselves are often close to the kinetic (diffusion) limit. Focusing on graphene as-grown on a copper substrate as a model 2D material/metal-supported electrode system, this study resolves the key electronic interactions in OS-ET, and identifies the role of graphene in modulating the electronic properties of the electrode/electrolyte interface. An integrated experimental-theoretical approach combining co-located multi-microscopy, centered on scanning electrochemical cell microscopy (SECCM), with Raman microscopy and field emission-scanning electron microscopy, together with rate theory and density functional theory calculations is used to address OS-ET kinetics of hexaamineruthenium (III/II) chloride, [Ru(NH3)6]3+/2+. The experimental methodology allows spatially-resolved electrochemical measurements to be targeted at distinct regions of monolayer, bilayer and multilayer graphene on copper, with high diffusion rates, to reveal ET kinetics in the order: monolayer > bilayer > multilayer. Theoretical and computational methods combining the Schmickler-Newns-Anderson model, transition state theory, and constant potential DFT reveal that the difference in kinetics at monolayer and bilayer graphene can be rationalized in the context of a dominantly adiabatic mechanism, where the addition of subsequent graphene layers increases the contact potential, producing an increase in the effective barrier to electron transfer. This study provides a roadmap for the integration of experiments and theory in order to understand the nature of heterogeneous electron transfer at complex nanostructured electrode materials.</p></div></div></div>

scholarly journals Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials

2021 ◽  
Author(s):  
Dan-Qing Liu ◽  
Minkyung Kang ◽  
David Perry ◽  
Chang-Hui Chen ◽  
Geoff West ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Electrode Materials ◽  
Copper Substrate ◽  
State Theory ◽  
Experimental Methodology ◽  
Diffusion Limit ◽  
Rate Theory ◽  
Multilayer Graphene ◽  
Contact Potential

<div><div><div><p>Outer-sphere electron transfer (OS-ET) is a cornerstone elementary electrochemical reaction, yet microscopic understanding is largely based on idealized theories, developed in isolation from experiments that themselves are often close to the kinetic (diffusion) limit. Focusing on graphene as-grown on a copper substrate as a model 2D material/metal-supported electrode system, this study resolves the key electronic interactions in OS-ET, and identifies the role of graphene in modulating the electronic properties of the electrode/electrolyte interface. An integrated experimental-theoretical approach combining co-located multi-microscopy, centered on scanning electrochemical cell microscopy (SECCM), with Raman microscopy and field emission-scanning electron microscopy, together with rate theory and density functional theory calculations is used to address OS-ET kinetics of hexaamineruthenium (III/II) chloride, [Ru(NH3)6]3+/2+. The experimental methodology allows spatially-resolved electrochemical measurements to be targeted at distinct regions of monolayer, bilayer and multilayer graphene on copper, with high diffusion rates, to reveal ET kinetics in the order: monolayer > bilayer > multilayer. Theoretical and computational methods combining the Schmickler-Newns-Anderson model, transition state theory, and constant potential DFT reveal that the difference in kinetics at monolayer and bilayer graphene can be rationalized in the context of a dominantly adiabatic mechanism, where the addition of subsequent graphene layers increases the contact potential, producing an increase in the effective barrier to electron transfer. This study provides a roadmap for the integration of experiments and theory in order to understand the nature of heterogeneous electron transfer at complex nanostructured electrode materials.</p></div></div></div>

Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

2019 ◽  
Author(s):  
Yan Wang ◽  
Sagar Udyavara ◽  
Matthew Neurock ◽  
C. Daniel Frisbie
Keyword(s):  
Electric Field ◽  
Hydrogen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Electronic Charge ◽  
Back Side ◽  
Gate Electrode ◽  
Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

scholarly journals Spectroscopic evidence for direct flavin-flavin contact in a bifurcating electron transfer flavoprotein

2020 ◽  
Vol 295 (36) ◽  
pp. 12618-12634
Author(s):  
H. Diessel Duan ◽  
Nishya Mohamed-Raseek ◽  
Anne-Frances Miller
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Protein Denaturation ◽  
Rhodopseudomonas Palustris ◽  
Density Functional Theory Calculations ◽  
Site Directed Mutagenesis ◽  
Functional Theory ◽  
Electron Transfer Flavoprotein ◽  
Midpoint Potential ◽  
Ct Complex

A remarkable charge transfer (CT) band is described in the bifurcating electron transfer flavoprotein (Bf-ETF) from Rhodopseudomonas palustris (RpaETF). RpaETF contains two FADs that play contrasting roles in electron bifurcation. The Bf-FAD accepts electrons pairwise from NADH, directs one to a lower-reduction midpoint potential (E°) carrier, and the other to the higher-E° electron transfer FAD (ET-FAD). Previous work noted that a CT band at 726 nm formed when ET-FAD was reduced and Bf-FAD was oxidized, suggesting that both flavins participate. However, existing crystal structures place them too far apart to interact directly. We present biochemical experiments addressing this conundrum and elucidating the nature of this CT species. We observed that RpaETF missing either FAD lacked the 726 nm band. Site-directed mutagenesis near either FAD produced altered yields of the CT species, supporting involvement of both flavins. The residue substitutions did not alter the absorption maximum of the signal, ruling out contributions from residue orbitals. Instead, we propose that the residue identities modulate the population of a protein conformation that brings the ET-flavin and Bf-flavin into direct contact, explaining the 726 nm band based on a CT complex of reduced ET-FAD and oxidized Bf-FAD. This is corroborated by persistence of the 726 nm species during gentle protein denaturation and simple density functional theory calculations of flavin dimers. Although such a CT complex has been demonstrated for free flavins, this is the first observation of such, to our knowledge, in an enzyme. Thus, Bf-ETFs may optimize electron transfer efficiency by enabling direct flavin-flavin contact.

scholarly journals Atomistic Modeling of Various Doped Mg2NiH4 as Conversion Electrode Materials for Lithium Storage

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 254 ◽  
Author(s):  
Zhao Qian ◽  
Guanzhong Jiang ◽  
Yingying Ren ◽  
Xi Nie ◽  
Rajeev Ahuja
Keyword(s):  
Density Functional ◽  
Electrode Materials ◽  
Electronic Conductivity ◽  
Specific Capacity ◽  
Density Functional Theory Calculations ◽  
Lithium Storage ◽  
Pure Material ◽  
Computational Screening ◽  
Electrochemical Capacity ◽  
Ti Doping

In this work, we have compared the potential applications of nine different elements doped Mg2NiH4 as conversion-type electrode materials in Li-ion batteries by means of state-of-the-art Density functional theory calculations. The electrochemical properties, such as specific capacity, volume change and average voltage, as well as the atomic and electronic structures of different doped systems have been investigated. The Na doping can improve the electrochemical capacity of the pristine material. Si and Ti doping can reduce the band gap and benefit the electronic conductivity of electrode materials. All of the nine doping elements can help to reduce the average voltage of negative electrodes and lead to reasonable volume changes. According to the computational screening, the Na, Si and Ti doping elements are thought to be promising to enhance the comprehensive properties of pure material. This theoretical study is proposed to encourage and expedite the development of metal-hydrides based lithium-storage materials.

Mechanistic Study of ROS-photogeneration by Pterin

Pteridines ◽  
2011 ◽  
Vol 22 (1) ◽  
pp. 73-76 ◽  
Author(s):  
Hong-Fang Ji ◽  
Liang Shen
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Transfer Reaction ◽  
Direct Electron Transfer ◽  
Density Functional Theory Calculations ◽  
Electron Transfer Reaction ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Direct Energy ◽  
Electronic Parameters

Abstract Pterins are widespread in biological systems and possess photosensitizing activities. In the present study, the photosensitization mechanism of acid form of pterin (PTA) and basic form of pterin (PTB) is investigated by means of density functional theory calculations. The reactive oxygen species-photogenerating pathways of the lowest triplet excited (T1) state PTA and PTB are proposed as follows. Through direct energy transfer, both T1 state PTA and PTB can photogenerate 1O2. Two possible O2 .−-generating pathways are proposed according to the electronic parameters of PTA and PTB: i) direct electron transfer from T1 state PTA and PTB to 3O2 and the electron transfer reaction is more favorable energetically for PTB in comparison with PTA; and ii) electron transfer from anion radical of PTA and PTB to 3O2.

Metal carbonyl complexes of potentially ambidentate 2,1,3-benzothiadiazole and 2,1,3-benzoselenadiazole acceptors

2017 ◽  
Vol 72 (11) ◽  
pp. 839-846
Author(s):  
Sebastian Plebst ◽  
Martina Bubrin ◽  
David Schweinfurth ◽  
Stanislav Záliš ◽  
Wolfgang Kaim
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Electron Transfer ◽  
Density Functional ◽  
Metal Carbonyl ◽  
Density Functional Theory Calculations ◽  
Carbonyl Complexes ◽  
Functional Theory ◽  
Metal Carbonyl Complexes ◽  
Reduced Forms

AbstractThe compounds [W(CO)5(btd)], [W(CO)5(bsd] and [Re(CO)3(bpy)(bsd)](BF4), btd=2,1,3-benzothiadiazole and bsd=2,1,3-benzoselenadiazole were isolated and characterized experimentally (crystal structure, spectroscopy, spectroelectrochemistry) and by density functional theory calculations. The results confirm single N-coordination in all cases, binding to Se was calculated to be less favorable. Studies of one-electron reduced forms indicate that the N-coordination is maintained during electron transfer.

scholarly journals The Role of Structural Flexibility in Plasmon-Driven Coupling Reactions: Kinetic Limitations in the Dimerization of Nitro-Benzenes

2021 ◽  
Author(s):  
Wouter Koopman ◽  
Evgenii Titov ◽  
Radwan Mohamed Sarhan ◽  
Tina Gaebel ◽  
Robin Schürmann ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Photoelectron Spectroscopy ◽  
Density Functional ◽  
Bond Activation ◽  
Density Functional Theory Calculations ◽  
Surface Enhanced Raman Spectroscopy ◽  
Bimolecular Reaction ◽  
Structural Flexibility ◽  
Coupling Reactions ◽  
Time Resolved

<div>The plasmon-driven dimerization of 4-nitrothiophenol (4NTP) to 4-4’-dimercaptoazobenzene (DMAB) has become a testbed for understanding bimolecular photoreactions enhanced by nanoscale metals, in particular, regarding the relevance of electron transfer and heat transfer from the metal to the molecule. By adding a methylene group between the thiol bond and the nitrophenyl, we add structural flexibility to the reactant molecule. Time-resolved surface-enhanced Raman-spectroscopy proves that this (4-nitrobenzyl)mercaptan (4NBM) molecule has a larger dimerization rate and dimerization yield than 4NTP and higher selectivity towards dimerization. X-ray photoelectron spectroscopy and density functional theory calculations show that the electron transfer would prefer activation of 4NTP over 4NBM. We conclude that the rate limiting step of this plasmonic reaction is the dimerization step, which is dramatically enhanced by the additional flexibility of the reactant. This study may serve as an example for using nanoscale metals to simultaneously provide charge carriers for bond activation and localized heat for driving bimolecular reaction steps. The molecular structure of reactants can be tuned to control the reaction kinetics.<br></div>

scholarly journals Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration

2019 ◽  
Author(s):  
Larrissa Y. Kunz ◽  
Lintao Bu ◽  
Brandon C. Knott ◽  
Cong Liu ◽  
Mark R. Nimlos ◽  
...  
Keyword(s):  
Electrostatic Interactions ◽  
Density Functional ◽  
Activation Barrier ◽  
Knudsen Diffusion ◽  
Transition States ◽  
Density Functional Theory Calculations ◽  
Detailed Examination ◽  
Amyl Alcohol ◽  
Primary Objective ◽  
Alcohol Dehydration

In the upgrading of biomass pyrolysis vapors to hydrocarbons, dehydration accomplishes a primary objective of removing oxygen and acidic zeolites represent promising catalysts for dehydration reaction. Here, we utilize density functional theory calculations to estimate adsorption energetics and intrinsic kinetics of alcohol dehydration over H-ZSM-5, H-BEA, and H-AEL zeolites. ONIOM calculations of adsorption energies were observed to be inconsistent when benchmarked against QM/Hartree-Fock and periodic boundary condition calculations. However, reaction coordinate calculations of adsorbed species and transition states were consistent across all levels considered. Comparison of ethanol, iso-propanol (IPA), and tert-amyl alcohol (TAA) over these three zeolites allowed for a detailed examination of how confinement impacts reaction mechanisms and kinetics. TAA, seen to proceed via a carbocationic mechanism, was found to have the lowest activation barrier, followed by IPA and then ethanol, both of which dehydrate via a concerted mechanism. Barriers in H-BEA were consistently found to be lower than in H-ZSM-5 and H-AEL, attributed to late transition states and either elevated strain or inaccurately estimating long-range electrostatic interactions in H-AEL, respectively. Molecular dynamics simulations revealed that the diffusivity of these three alcohols in H-ZSM-5 are significantly overestimated by Knudsen diffusion, which will complicate experimental efforts to develop a kinetic model for catalytic fast pyrolysis.

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