skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Electrical Double Layer Spillover Drives Coupled Electron- and Phase-Transfer Reactions at Electrode/Toluene/Water Three-Phase Interfaces
Title: Electrical Double Layer Spillover Drives Coupled Electron- and Phase-Transfer Reactions at Electrode/Toluene/Water Three-Phase Interfaces
A mechanism for the concerted pathway of coupled electron- and phase-transfer reactions (CEPhT) is proposed. CEPhT at three-phase interfaces formed by a solid electrode, an insulating organic solvent, and an aqueous electrolyte is driven by electric double layer (EDL) spillover, with significant electrostatic potential gradients extending a few nanometers into the insulating phase. This EDL spillover phenomenon is studied using scanning electrochemical cell microscopy to interrogate the oxidation of ferrocene in toluene to ferrocenium in water, (Fc)tol → (Fc+)aq + e–. Finite element method simulations of the electrostatic potential distribution and species concentration profiles enable the calculation of complete i–E curves that incorporate mass transport, electron transfer, phase transfer, and the EDL structure. Simulated and experimental i–E traces show good agreement in the current magnitude and the effect of the supporting electrolyte, identifying an unexpected dependence of overall reaction kinetics on the concentration of the supporting electrolyte in the aqueous phase due to EDL spillover. An interfacial toluene/water mixing region generates a unique electrochemical microenvironment where concerted electron transfer and solvent shell replacement facilitate CEPhT. Kinetic expressions for concerted and sequential CEPhT mechanisms highlight the role of this interfacial environment in controlling the rate of CEPhT. These combined experimental and simulated results are the first to support a concerted mechanism for CEPhT where (Fc)tol is transported to the interfacial mixing region at the three-phase interface, where it undergoes oxidation and phase transfer. EDL spillover can be leveraged for engineering sample geometries and electrostatic microenvironments to drive electrochemical reactivity in classically forbidden regions, e.g., insulating solvents and gases.  more » « less
Award ID(s):
2300863
PAR ID:
10598001
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
American Chemical Society
Date Published:
Journal Name:
Journal of the American Chemical Society
Volume:
146
Issue:
44
ISSN:
0002-7863
Page Range / eLocation ID:
30464-30473
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, Nature Communications)
    Abstract The hydrated electron, e–(aq), has attracted much attention as a central species in radiation chemistry. However, much less is known about e–(aq)at the water/air surface, despite its fundamental role in electron transfer processes at interfaces. Using time-resolved electronic sum-frequency generation spectroscopy, the electronic spectrum of e–(aq)at the water/air interface and its dynamics are measured here, following photo-oxidation of the phenoxide anion. The spectral maximum agrees with that for bulk e–(aq)and shows that the orbital density resides predominantly within the aqueous phase, in agreement with supporting calculations. In contrast, the chemistry of the interfacial hydrated electron differs from that in bulk water, with e–(aq)diffusing into the bulk and leaving the phenoxyl radical at the surface. Our work resolves long-standing questions about e–(aq)at the water/air interface and highlights its potential role in chemistry at the ubiquitous aqueous interface. 
    more » « less
  2. ; ; ; ; ; (, Chemical Science)
    null (Ed.)
    The super electron donor (SED) ability of 2-azaallyl anions has recently been discovered and applied to diverse reactivity, including transition metal-free cross-coupling and dehydrogenative cross-coupling processes. Surprisingly, the redox properties of 2-azaallyl anions and radicals have been rarely studied. Understanding the chemistry of elusive species is the key to further development. Electrochemical analysis of phenyl substituted 2-azaallyl anions revealed an oxidation wave at E 1/2 or E pa = −1.6 V versus Fc/Fc + , which is ∼800 mV less than the reduction potential predicted ( E pa = −2.4 V vs. Fc/Fc + ) based on reactivity studies. Investigation of the kinetics of electron transfer revealed reorganization energies an order of magnitude lower than commonly employed SEDs. The electrochemical study enabled the synthetic design of the first stable, acyclic 2-azaallyl radical. These results indicate that the reorganization energy should be an important design consideration for the development of more potent organic reductants. 
    more » « less
  3. ; ; ; ; ; ; ; ; (, Proceedings of the National Academy of Sciences)
    Highly concentrated aqueous electrolytes (termed water-in-salt electrolytes, WiSEs) at solid-liquid interfaces are ubiquitous in myriad applications including biological signaling, electrosynthesis, and energy storage. This interface, known as the electrical double layer (EDL), has a different structure in WiSEs than in dilute electrolytes. Here, we investigate how divalent salts [zinc bis(trifluoromethylsulfonyl)imide, Zn(TFSI)2], as well as mixtures of mono- and divalent salts [lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) mixed with Zn(TFSI)2], affect the short- and long-range structure of the EDL under confinement using a multimodal combination of scattering, spectroscopy, and surface forces measurements. Raman spectroscopy of bulk electrolytes suggests that the cation is closely associated with the anion regardless of valency. Wide-angle X-ray scattering reveals that all bulk electrolytes form ion clusters; however, the clusters are suppressed with increasing concentration of the divalent ion. To probe the EDL under confinement, we use a Surface Forces Apparatus and demonstrate that the thickness of the adsorbed layer of ions at the interface grows with increasing divalent ion concentration. Multiple interfacial layers form following this adlayer; their thicknesses appear dependent on anion size, rather than cation. Importantly, all electrolytes exhibit very long electrostatic decay lengths that are insensitive to valency. It is likely that in the WiSE regime, electrostatic screening is mediated by the formation of ion clusters rather than individual well-solvated ions. This work contributes to understanding the structure and charge-neutralization mechanism in this class of electrolytes and the interfacial behavior of mixed-electrolyte systems encountered in electrochemistry and biology. 
    more » « less
  4. ; (, The Journal of Physical Chemistry C)
    Density functional theory (DFT) is used to investigate the conversion from a solvent incorporated pseudo-polymorph into a single component monolayer. Calculations of thermodynamic properties both for the surfaces in contact with gas phase and with solvent are reported. In the case of wetted surfaces, a simple bond-additivity model, first proposed by Campbell and modified here, is used to augment the DFT calculations. The model predicts a dramatic reduction in desorption energies in solvent as compared to gas phase. Eyring’s reaction rate theory is used to predict limiting desorption rates for guest (solvent) molecules from the pockets in the pseudo-polymorph and for cobalt octaethylporphyrin (COEP) molecules in all structures. The pseudo-polymorph studied here is a nearly rectangular lattice (REC) composed of two CoOEP and 2 molecules of either 1,2,4-trichlorobenzene (TCB) or toluene (TOL) supported on 63 atoms of Au(111). At sufficiently high initial concentrations of CoOEP, only a hexagonal unit cell (HEX) with two molecules of CoOEP, supported on 50 atoms of gold is observed. Experimentally, the TCB-REC structure is more stable than the TOL-REC structure existing in solution at initial mM concentrations of CoOEP in TCB as opposed to initial M concentration of CoOEP in toluene. Calculations here show that the HEX structure is the thermodynamically stable structure at all practical concentrations of CoOEP. Once the REC structure forms kinetically at low concentration because of the vast excess of solvent on the surface, it is difficult to convert to the more stable HEX structure. The difference in stability is primarily due to the difference in electronic adsorption energy of the solvents (TOL or TCB) and to the very low desorption rate of CoOEP. The adsorption energy of TCB has two important contributors: the adsorption energy onto Au alone, and the intermolecular interactions between TCB and the CoOEP host lattice. Neither factor can be neglected. We also find that planar adsorption of both TOL and TCB on Au(111) is the energetically preferred orientation when space is available on the surface. Rates of desorption are very sensitive to the solvent free activation energy and to the thermodynamic parameters required to convert the solvent free activation energy to one for the solvated surface. Small changes in the computed energy (of the order of 5%) can lead to one order of magnitude change in rates. Further, the solvation model used does not provide the barrier to adsorption in solution needed to determine values for the desorption activation energy. Thus, the rates computed here for desorption into solvent are limiting values. 
    more » « less
  5. ; (, Chemical Communications)
    Electrochemical energy systems such as batteries, water electrolyzers, and fuel cells are considered as promising and sustainable energy storage and conversion devices due to their high energy densities and zero or negative carbon dioxide emission. However, their widespread applications are hindered by many technical challenges, such as the low efficiency and poor long-term cyclability, which are mostly affected by the changes at the reactant/electrode/electrolyte interfaces. These interfacial processes involve ion/electron transfer, molecular/ion adsorption/desorption, and complex interface restructuring, which lead to irreversible modifications to the electrodes and the electrolyte. The understanding of these interfacial processes is thus crucial to provide strategies for solving those problems. In this review, we will discuss different interfacial processes at three representative interfaces, namely, solid–gas, solid–liquid, and solid–solid, in various electrochemical energy systems, and how they could influence the performance of electrochemical systems. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email