Pressure effects and solvent dynamics in the electrochemical kinetics of the tris(hexafluoroacetylacetonato)ruthenium(III)/(II) couple in nonaqueous solvents

2001 ◽  
Vol 79 (5-6) ◽  
pp. 841-847 ◽  
Author(s):  
Jinkui Zhou ◽  
Thomas W Swaddle
Keyword(s):  
Free Energy ◽  
Activation Barrier ◽  
Electrode Reaction ◽  
Pressure Effects ◽  
Electrochemical Kinetics ◽  
Free Energy Barrier ◽  
Exchange Reactions ◽  
Electrode Processes ◽  
Solvent Dynamics ◽  
Kinetics Of

Rate constants and reactant diffusion coefficients for the Ru(hfac)30/– electrode reaction have been measured at 25°C as functions of pressure (0-200 MPa) in acetone, acetonitrile, methanol, and propylene carbonate. In sharp contrast to the negative volumes of activation ΔVex‡ found for the corresponding bimolecular self-exchange reaction in organic solvents, the volumes of activation ΔVel‡ for the electrode reaction are markedly positive, ranging from 8 to 12 cm3 mol–1. The volumes of activation ΔVdiff‡ for reactant diffusion (which can be equated to the volume of activation ΔVvisc‡ for viscous flow) range from 12 to 19 cm3 mol–1. For the Debye solvents acetonitrile and acetone at least, ΔVel‡ is given within the experimental uncertainty by ΔVdiff‡ + (ΔVex‡/2). In this relation, the numerical value of ΔVdiff‡ represents indirectly the dominant contribution of solvent dynamics (solvent friction) to ΔVel‡, and ΔVex‡/2 represents the pressure dependence of the free-energy barrier height for the electrode reaction. It is proposed that solvent friction is important in nonaqueous electrode processes but not in the corresponding bimolecular self-exchange reactions because the free-energy activation barrier is twice as high in the latter.Key words: electrode reaction kinetics, solvent dynamics, electron transfer mechanisms, pressure effects, volume of activation.

Volumes of activation for electrode processes of various charge-types in nonaqueous solvents

2001 ◽  
Vol 79 (12) ◽  
pp. 1864-1869 ◽  
Author(s):  
Mitsuru Matsumoto ◽  
Delanie Lamprecht ◽  
Michael R North ◽  
Thomas W Swaddle
Keyword(s):  
Electron Transfer ◽  
Reaction Rate ◽  
Electrode Reaction ◽  
State Theory ◽  
Exchange Reactions ◽  
Pt Electrode ◽  
Electrode Processes ◽  
Solvent Dynamics ◽  
The Mean ◽  
Dynamical Control

Volumes of activation (ΔV‡el) are reported for electron transfer at a Pt electrode of Mn(CN-cyclo-C6H11)62+/+ in acetonitrile, acetone, methanol, and propylene carbonate, and of Fe(phen)33+/2+ in acetonitrile. In all cases, ΔV‡el is markedly positive, whereas for the homogeneous self-exchange reactions of these couples in the same solvents the corresponding parameter is known to be strongly negative. The rate constants for the electrode reactions correlate loosely with the mean reactant diffusion coefficients (i.e., with solvent fluidity) and the ΔV‡el values with the volumes of activation for diffusion (i.e., for viscous flow), consistent with solvent dynamical control of the electrode reaction rate in organic solvents. A detailed analysis of ΔV‡el values of the kind presented for a couple with an uncharged member (Zhou and Swaddle, Can. J. Chem. 79, 841 (2001)) fails, however, either because of ion-pairing effects with these more highly charged couples or because of breakdown of transition-state theory in predicting the contribution of the activational barrier. Attempts to measure ΔV‡el for the oxidation of the uncharged molecule ferrocene at various electrodes in acetonitrile were unsuccessful, although ΔV‡el was again seen to be clearly positive.Key words: electrode kinetics, volumes of activation, nonaqueous electron transfer, solvent dynamics.

scholarly journals Co-Crystallization Kinetics of 2:1 Benzoic Acid–Sodium Benzoate Co-Crystal: The Effect of Templating Molecules in a Solution

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 812
Author(s):  
Freshsya Zata Lini ◽  
Dhanang Edy Pratama ◽  
Tu Lee
Keyword(s):  
Growth Rate ◽  
Free Energy ◽  
Crystal Growth ◽  
Energy Barrier ◽  
Crystal Growth Rate ◽  
Supramolecular Assemblies ◽  
Solution Phase ◽  
Crystal Habit ◽  
Free Energy Barrier ◽  
Kinetics Of

The addition of dissolved templating molecules in crystallization will create “supramolecular assemblies” within the solution, serving as “anchor points” for the solute molecules to nucleate and grow. In this work, nucleation and crystal growth kinetics of 2:1 benzoic acid (HBz)–sodium benzoate (NaBz) co-crystallization with or without templates in a solution were analyzed by monitoring the concentration of the mother liquor during cooling crystallization. The results showed that the addition of the dissolved 2:1 or 1:1 HBz–NaBz co-crystals as templating molecules could reduce the critical free energy barrier of 2:1 HBz–NaBz co-crystal during its nucleation, but did not significantly affect the order of crystal growth rate. On the other hand, the critical free energy barrier of the nucleation process was increased if dissolved NaBz was used as a templating molecule, while a significant rise in the order of crystal growth rate occurred. The crystal habit obtained from the NaBz-templated system was needle-like, suggesting that sodium–sodium coordination chains of NaBz supramolecular assemblies in the solution phase were responsible for creating elongated crystals. Conversely, a large prismatic crystal habit found in non-templated and 2:1 and 1:1 HBz–NaBz co-crystal-templated systems implied that those templating molecules formed sparsely interconnected supramolecular assemblies in the solution phase.

scholarly journals The kinetics of electrode reactions. I and II

1938 ◽  
Vol 169 (937) ◽  
pp. 206-234 ◽  
Keyword(s):  
Electrode Potential ◽  
Surface Reaction ◽  
Reference Electrode ◽  
Electrode Reaction ◽  
Potential Difference ◽  
Concentration Difference ◽  
Electrode Processes ◽  
Electrode Reactions ◽  
Concentration Changes ◽  
Kinetics Of

In any surface reaction taking place in a Solution, it is clear that the concentration of the reactants in the vicinity of the surface must fall. If the concentration in the bulk of the solution remains constant, a steady state may finally be reached, in which the rate of replenishment of the solution in this region, from the bulk, is equal to the rate at which the reactant in question is used up. But, in general, such a state is only attained when the concentration at the surface is less than that in the rest of the solution. If the reaction considered is an electrode reaction, these concentration changes may affect the electrode potential. This question is therefore of importance in the study of overpotential, and of the kinetics of electrode processes generally. The overpotential at an electrode is defined as the potential difference between this electrode and a similar unpolarized reversible electrode in the same solution. In practice this reference electrode is usually situated outside the region affected by the concentration changes near the electrode at which the reaction is taking place. The measured potential difference between the two electrodes, i.e. the measured overpotential, may therefore include a term due to the concentration difference.

scholarly journals Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells

2017 ◽  
Vol 19 (4) ◽  
pp. 2666-2673 ◽  
Author(s):  
Tao Cheng ◽  
William A Goddard ◽  
Qi An ◽  
Hai Xiao ◽  
Boris Merinov ◽  
...  
Keyword(s):  
Free Energy ◽  
Energy Barrier ◽  
Reduction Reaction ◽  
Free Energy Barrier ◽  
Hydrogen Fuel Cells ◽  
Hydrogen Fuel ◽  
Applied Potential ◽  
Mechanism And Kinetics ◽  
Kinetics Of ◽  
Electrocatalytic Reaction

Free energy barrier as a function of applied potential for the Oxygen Reduction Reaction (ORR) on Pt(111) surface.

scholarly journals Electrochemical kinetics of cerium selenide nano-pebbles: Design of device grade symmetric configured wide-potential flexible solid-state supercapacitor

2021 ◽  
Author(s):  
Bidhan Pandit ◽  
Akansha Agrawal ◽  
Priyanka Patel ◽  
Babasaheb R. Sankapal
Keyword(s):  
Free Energy ◽  
Energy Storage ◽  
Solid State ◽  
Flexible Electronics ◽  
Electrochemical Kinetics ◽  
Roll To Roll ◽  
Mechanical Bending ◽  
Kinetics Of ◽  
Wide Potential ◽  
State Of Art

Next generation portable flexible electronics appliances necessitate liquid-free energy storage supercapacitor devices to get rid of leakage along with mechanical bending compatible to roll-to-roll technologies. Hence, state of art is...

Molecular Basis of Glucose Transport Mechanism in Plants

2019 ◽  
Author(s):  
Balaji Selvam ◽  
Ya-Chi Yu ◽  
Liqing Chen ◽  
Diwakar Shukla
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Molecular Dynamics Simulations ◽  
Conformational Changes ◽  
Transport Mechanism ◽  
Conformational Dynamics ◽  
Site Directed Mutagenesis ◽  
Free Energy Barrier ◽  
Transport Cycle ◽  
Dynamics Simulations

<p>The SWEET family belongs to a class of transporters in plants that undergoes large conformational changes to facilitate transport of sugar molecules across the cell membrane. However, the structures of their functionally relevant conformational states in the transport cycle have not been reported. In this study, we have characterized the conformational dynamics and complete transport cycle of glucose in OsSWEET2b transporter using extensive molecular dynamics simulations. Using Markov state models, we estimated the free energy barrier associated with different states as well as 1 for the glucose the transport mechanism. SWEETs undergoes structural transition to outward-facing (OF), Occluded (OC) and inward-facing (IF) and strongly support alternate access transport mechanism. The glucose diffuses freely from outside to inside the cell without causing major conformational changes which means that the conformations of glucose unbound and bound snapshots are exactly same for OF, OC and IF states. We identified a network of hydrophobic core residues at the center of the transporter that restricts the glucose entry to the cytoplasmic side and act as an intracellular hydrophobic gate. The mechanistic predictions from molecular dynamics simulations are validated using site-directed mutagenesis experiments. Our simulation also revealed hourglass like intermediate states making the pore radius narrower at the center. This work provides new fundamental insights into how substrate-transporter interactions actively change the free energy landscape of the transport cycle to facilitate enhanced transport activity.</p>

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