Search results for "proton-coupled electron transfer"

Proton coupled electron transfer of ubiquinone Q2 incorporated in a self-assembled monolayer.

2011

We present a complete study of the reduction of ubiquinone Q(2) (UQ(2)) in simpler aqueous medium, over a pH range of 2.5 to 12.5. The short isoprenic chain ubiquinones (UQ(2)) were incorporated in a self-assembled monolayer. Under these conditions, the global 2e(-) electrochemical reaction can be described on the basis of a nine-member square scheme. The thermodynamic constants of the system were determined. The global 2e(-) process is controlled by the uptake of the second electron. The elementary electrochemical rate constants obtained by fitting of the experimental rate constant were k(s4) = 1.5 s(-1) for QH˙(+)(2)↔ QH(2), k(s5) = 1.5 s(-1) for QH˙↔ QH(-) and k(s6) = 1 s(-1) for Q˙(-)↔ …

Hole Localization and Thermochemistry of Oxidative Dehydrogenation of Aqueous Rutile TiO2(110)

2012

Rate Theory for Electrocatalytic Systems: Fixed Potential Formulation for General, Electron Transfer, and Proton-Coupled Electron Transfer Reactions

2019

Atomistic modeling of electrocatalytic reactions is most naturally conducted within the grand canonical ensemble (GCE) which enables fixed chemical potential calculations. While GCE has been widely adopted for modeling electrochemical and electrocatalytic thermodynamics, the electrochemical reaction rate theory within GCE is lacking. Molecular and condensed phase rate theories are formulated within microcanonical and canonical ensembles, respectively, but electrocatalytic systems described within the GCE require extension of the conventionally used rate theories for computation reaction rates at fixed electrode potentials. In this work, rate theories from (micro) canonical ensemble are gene…

Unified Rate Theory of Electrochemistry and Electrocatalysis: Fixed Potential Formulation for General, Electron Transfer, and Proton-Coupled Electron…

2019

Atomistic modeling of electrocatalytic reactions is most naturally conducted within the grand canonical ensemble (GCE) which enables fixed chemical potential calculations. While GCE has been widely adopted for modeling electrochemical and electrocatalytic thermodynamics, the electrochemical reaction rate theory within GCE is lacking. Molecular and condensed phase rate theories are formulated within microcanonical and canonical ensembles, respectively, but electrocatalytic systems described within the GCE require extension of the conventionally used rate theories for computation reaction rates at fixed electrode potentials. In this work, rate theories from (micro)canonical ensemble are gener…

Computational Screening of Doped Graphene Electrodes for Alkaline CO2 Reduction

2020

The electrocatalytic CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) is considered as one of the most promising approaches to synthesizing carbonaceous fuels and chemicals without utilizing fossil resources. However, current technologies are still in the early phase focusing primarily on identifying optimal electrode materials and reaction conditions. Doped graphene-based materials are among the best CO<sub>2</sub>RR electrocatalysts and in the present work we have performed a computational screening study to identify suitable graphene catalysts for CO<sub>2</sub>RR to CO under alkaline conditions. Several types of modified-graphene frame…

Proton-Coupled Electron Transfer in Ferrocenium–Phenolate Radicals

2013

Electron and proton transfer (ET, PT) can be intimately coupled, provided suitable redox and acid/base sites are available. The amide-linked ferrocene–phenol H-1 is deprotonated to the phenolate [1]– by phosphazene bases and oxidized to the ferrocenium ion [H-1]+ by silver hexafluoroantimonate. Concomitant oxidation and deprotonation yields the radical [1]•, featuring a characteristic near-IR absorption band. The ground state of [1]• is best described as the ferrocenium–phenolate zwitterion [1b]• with a dynamic dissymmetric N···H···O hydrogen bond (PT). The ferrocenium–iminolate N···H–O tautomer [1b]•-NHO′ can undergo a thermal structural rearrangement to the high-energy OH···O tautomer [1b…

Grand canonical rate theory for electrochemical and electrocatalytic systems I: General formulation and proton-coupled electron transfer reactions

2020

A generally valid rate theory at fixed potentials is developed to treat electrochemical and electrocatalytic potential-dependent electron, proton, and proton-coupled electron reactions. Both classical and quantum reactions in adiabatic and non-adiabatic limits are treated. The applicability and new information obtained from the theory is demonstrated for the gold catalyzed acidic Volmer reaction.

Electrochemical and Spectroelectrochemical Behavior of a Tetracyanotriphenodioxazine in Solution and Thin-Films

2018

International audience; We report the electrochemical behavior of a tetracyano triphenodioxazine bearing two triisopropylsilylethynyl moieties (TiPS‐TPDO‐tetraCN) during its reduction studied either in solution or after vacuum evaporation deposition on indium tin oxide (ITO) support. While in dichloromethane, it typically proceeds in two successive monoelectronic reactions, in acetonitrile, the mechanism appears more complex. Fine analysis of the spectroelectrochemical results combined with simulation of the voltammograms with various amount of water suggest the involvement of water and of a restructured dianion in the electrochemical process. In the solid‐state, the formation of the diprot…

Photoinduced Electron Transfer Reactions in a Porphyrin−Viologen Complex:  Observation of S2 to S1 Relaxation and Electron Transfer from the S2 State

1999

Photoinduced Energy Transfer Reactions in a Porphyrin-Viologen Complex: Observation of S2 to S1 Relaxation and Electron Transfer from the S2 state

Grand canonical ensemble approach to electrochemical thermodynamics, kinetics, and model Hamiltonians

2021

The unique feature of electrochemistry is the ability to control reaction thermodynamics and kinetics by the application of electrode potential. Recently, theoretical methods and computational approaches within the grand canonical ensemble (GCE) have enabled to explicitly include and control the electrode potential in first principles calculations. In this review, recent advances and future promises of GCE density functional theory and rate theory are discussed. Particular focus is devoted to considering how the GCE methods either by themselves or combined with model Hamiltonians can be used to address intricate phenomena such as solvent/electrolyte effects and nuclear quantum effects to pr…