6 research outputs found
Analyzing Benzene and Cyclohexane Emulsion Droplet Collisions on Ultramicroelectrodes
We
report the collisions of single emulsion oil droplets with extremely
low dielectric constants (e.g., benzene, Δ of 2.27, or cyclohexane,
Δ of 2.02) as studied via emulsion droplet reactor (EDR) on
an ultramicroelectrode (UME). By applying appropriate potentials to
the UME, we observed the electrochemical effects of single-collision
signals from the bulk electrolysis of single emulsion droplets. Different
hydrophobic redox species (ferrocene, decamethyl-ferrocene, or metalloporphyrin)
were trapped in a mixed benzene (or cyclohexane) oil-in-water emulsion
using an ionic liquid as the supporting electrolyte and emulsifier.
The emulsions were prepared using ultrasonic processing. Spike-like
responses were observed in each <i>iât</i> response
due to the complete electrolysis of all of the above-mentioned redox
species within the droplet. On the basis of these single-particle
collision results, the collision frequency, size distribution, <i>iât</i> decay behavior of the emulsion droplets, and
possible mechanisms are analyzed and discussed. This work demonstrated
that bulk electrolysis can be achieved in a few seconds in these attoliter
reactors, suggesting many applications, such as analysis and electrosynthesis
in low dielectric constant solvents, which have a much broader potential
window
Single Organic Droplet Collision Voltammogram via Electron Transfer Coupled Ion Transfer
Single-emulsion
toluene oil droplets (femtoliter) containing a
hydrophobic redox probe that are dispersed in water stochastically
collide with an ultramicroelectrode (UME). The fast-scan cyclic voltammetry
(FSCV) or Fourier-transformed sinusoidal voltammetry (FTSV) is applied:
the UME was scanned with a fast, repetitive triangular, or sinusoidal
potential, and its current in time/frequency domains were monitored.
The electron transfer at the UME/oil interface is coupled with ion
transfer at the oil/water interface. Thus, the obtained transient
voltammograms of a myriad of ions were used to estimate thermodynamics
of ion transfer at the toluene/water interface. Additionally, the
single-droplet voltammogram combined with finite element simulations
reveal the dropletâs size and shape distributions. Four collision
mechanisms with new physical insights were also uncovered via comprehensive
analysis of phase angle in the frequency domain, time domain FSCVs,
and finite element simulations
Probing Ion Transfer across LiquidâLiquid Interfaces by Monitoring Collisions of Single Femtoliter Oil Droplets on Ultramicroelectrodes
We describe a method of observing
collisions of single femtoliter
(fL) oil (i.e., toluene) droplets that are dispersed in water on an
ultramicroelectrode (UME) to probe the ion transfer across the oil/water
interface. The oil-in-water emulsion was stabilized by an ionic liquid,
in which the oil droplet trapped a highly hydrophobic redox probe,
rubrene. The ionic liquid also functions as the supporting electrolyte
in toluene. When the potential of the UME was biased such that rubrene
oxidation would be possible when a droplet collided with the electrode,
no current spikes were observed. This implies that the rubrene radical
cation is not hydrophilic enough to transfer into the aqueous phase.
We show that current spikes are observed when tetrabutylammonium trifluoromethanesulfonate
or tetrahexylammonium hexafluorophosphate are introduced into the
toluene phase and when tetrabutylammonium perchlorate is introduced
into the water phase, implying that the ion transfer facilitates electron
transfer in the droplet collisions. The current (<i>i</i>)âtime (<i>t</i>) behavior was evaluated quantitatively,
which indicated the ion transfer is fast and reversible. Furthermore,
the size of these emulsion droplets can also be calculated from the
electrochemical collision. We further investigated the potential dependence
on the electrochemical collision response in the presence of tetrabutylammonium
trifluoromethanesulfonate in toluene to obtain the formal ion transfer
potential of tetrabutylammonium across the toluene/water interface,
which was determined to be 0.754 V in the inner potential scale. The
results yield new physical insights into the charge balance mechanism
in emulsion droplet collisions and indicate that the electrochemical
collision technique can be used to probe formal ion transfer potentials
between water and solvents with very low (Δ < 5) dielectric
constants
A Method to Inhibit Disproportionation of Mn<sup>3+</sup> for Low-Cost MnâFe All-Flow Battery
Among
battery technologies considered for large-scale energy storage,
manganese-based redox flow batteries have been extremely attractive
due to the low cost of materials. Impeding its industrial adoption
is the precipitation of MnO2 due to disproportionation
of Mn3+. In this work, we overcome the formation of MnO2 precipitates through complexation of Mn3+ with
Clâ ions. By virtue of the stable [MnCl4(H2O)2]â complex, an inexpensive
and scalable FeâMn flow battery was demonstrated using Mn3+/Mn2+ and Fe3+/Fe2+ redox
couples as catholyte and anolyte, respectively. The flow battery achieved
an output voltage of 0.7 V and current density of up to 160 mA cmâ2
Observing Discrete Blocking Events at a Polarized Micro- or Submicro-Liquid/Liquid Interface
Single-entity collisional electrochemistry (SECE), a
subfield of
single-entity electrochemistry, enables directly characterizing entities
and particles in the electrolyte solution at the single-entity resolution.
Blockade SECE at the traditional solid ultramicroelectrode (UME)/electrolyte
interface suffers from a limitation: only redox-inactive particles
can be studied. The wide application of the classical Coulter counter
is restricted by the rapid translocation of entities through the orifice,
which results in a remarkable proportion of undetected signals. In
response, the blocking effect of single charged conductive or insulating
nanoparticles (NPs) at low concentrations for ion transfer (IT) at
a miniaturized polarized liquid/liquid interface was successfully
observed. Since the particles are adsorbed at the liquid/liquid interface,
our method also solves the problem of the Coulter counter having a
too-fast orifice translocation rate. The decreasing quantal staircase/step
current transients are from landings (controlled by electromigration)
of either conductive or insulating NPs onto the interface. This interfacial
NP assembly shields the IT flux. The size of each NP can be calculated
by the step height. The particle size measured by dynamic light scattering
(DLS) is used for comparison with that calculated from electrochemical
blocking events, which is in fairly good agreement. In short, the
blocking effect of IT by single entities at micro- or submicro-liquid/liquid
interface has been proven experimentally and is of great reference
in single-entity detection
Oxygen reduction at soft interfaces catalyzed by in situ-generated reduced graphene oxide
Face to face: Flakes of reduced graphene oxide, synthesizedâ
in situ at the liquid/liquid interface from a grapheneâoxide precursor, are capable of catalyzing the biphasic reduction of protons to hydrogen peroxide in the presence of molecular oxygen and an organic solubilized electron donor. This offers a new perspective for the bulk production of a green oxidant through biphasic electrolysi