The atomic‐scale structure of the interface between a transition metal oxide and aqueous electrolyte regulates the interfacial chemical reactions fundamental to (photo)electrochemical energy conversion and electrode degradation. Measurements that probe oxide–electrolyte interfaces in situ provide important details of ion and solvent arrangements, but atomically precise structural models do not exist for common oxide–electrolyte interfaces far from equilibrium. Using a novel cell, the structure of the hematite (α‐Fe2O3) (
Prussian blue analogs (PBAs) are used as electrode materials in energy storage and water deionization cells due to their reversible cation intercalation capability. Despite extensive research on their performance and intercalation mechanisms, little attention has been given to their behavior under open-circuit conditions. Recent studies using symmetrical PBA electrodes in two electrode deionization cells reported that after constant current cycling in dilute NaCl (<0.2 M), the cell voltage dropped under open-circuit conditions, which substantially increased the amount of energy consumed for deionization. However, it remains unclear which electrode (anode/cathode) experienced potential drift and if it was influenced by the low salinity of the electrolyte. Here, we performed a series of electrochemical experiments under different charging and discharging regimes and electrolyte compositions to determine the processes that contributed most significantly to open-circuit potential drift. The data indicated that charge redistribution within the electrode was the main contributor to open circuit potential drift, with electrode dissolution and parasitic reactions playing negligible roles. A one-dimensional finite element model was constructed to simulate charge redistribution by accounting for cation diffusion under open-circuit conditions. The open-circuit potential profiles generated by the model were validated against experimental trends, confirming the occurrence of charge redistribution. A Monte Carlo analysis of the model was conducted to determine the relationship of potential drift to key factors such as applied current, electrode thickness, diffusion coefficient of intercalating ions, and intercalation capacity. Subsequently, a dimensionless number (
- NSF-PAR ID:
- 10472210
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 170
- Issue:
- 11
- ISSN:
- 0013-4651
- Format(s):
- Medium: X Size: Article No. 110503
- Size(s):
- ["Article No. 110503"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract )–electrolyte interface is measured under controlled electrochemical bias using synchrotron crystal truncation rod X‐ray scattering. At increasingly cathodic potentials, charge‐compensating protonation of surface oxygen groups increases the coverage of specifically bound water while adjacent water layers displace outwardly and became disordered. Returning to open circuit potential leaves the surface in a persistent metastable state. Therefore, the flux of current and ions across the interface is regulated by multiple electrolyte layers whose specific structure and polarization change in response to the applied potential. The study reveals the complex environment underlying the simplified electrical double layer models used to interpret electrochemical measurements and emphasizes the importance of condition‐specific structural characterization for properly understanding catalytic processes at functional transition metal oxide–electrolyte interfaces. -
more » « less
A theoretical analysis on crack formation and propagation was performed based on the coupling between the electrochemical process, classical elasticity, and fracture mechanics. The chemical potential of oxygen, thus oxygen partial pressure, at the oxygen electrode-electrolyte interface (
-
more » « less
Cyclic voltammetry was applied to investigate the permselective properties of electrode-supported ion-exchange polymer films intended for use in future molecular-scale spectroscopic studies of bipolar membranes. The ability of thin ionomer film assemblies to exclude mobile ions charged similarly to the polymer (co-ions) and accumulate ions charged opposite to the polymer (counterions) was scrutinized through use of the diffusible redox probe molecules [Ru(NH3)6]3+and [IrCl6]2−. With the anion exchange membrane (AEM) phase supported on a carbon disk electrode, bipolar junctions formed by addition of a cation exchange membrane (CEM) overlayer demonstrated high selectivity toward redox ion extraction and exclusion. For junctions formed using a Fumion®AEM phase and a Nafion®overlayer, [IrCl6]2−ions exchanged into Fumion®prior to Nafion®overcoating remained entrapped and the Fumion®excluded [Ru(NH3)6]3+ions for durability testing periods of more than 20 h under conditions of interest for eventual
in situ spectral measurements. Experiments with the Sustainion®anion exchange ionomer uncovered evidence for [IrCl6]2−ion coordination to pendant imidazolium groups on the polymer. A cyclic voltammetric method for estimation of the effective diffusion coefficient and equilibrium extraction constant for redox active probe ions within inert, uniform density electrode-supported thin films was applied to examine charge transport mechanisms. -
more » « less
Understanding the current response at an electrode from suspended solid particles in an electrolyte is crucial for developing materials to be used in semi-solid electrodes for energy storage applications. Here, an analytical model is proposed to predict and understand the current response from non-disintegrable solid particles at a rotating disk electrode. The current is shown to be limited by a combination of ion diffusion within the solid particle and the mean residence time of the particle at the rotating disk electrode. This results in a relationship between current and angular frequency of
-
more » « less
Abstract The distortion of the charge cloud around a uniformly charged, dielectric, rigid sphere that translates and rotates in an unbounded binary, symmetric electrolyte at zero Reynolds number is examined. The zeta potential of the particle ζ is assumed small relative to the thermal voltage scale. It is assumed that the equilibrium structure of the cloud is slightly distorted, which requires that the Péclet numbers characterizing distortion due to particle translation,
, and rotation, , are small compared to unity. Here, a is radius of the particle;D is the ionic diffusion coefficient;and , where U Ω and are employed to calculate the nonequilibrium structure of the cloud, whence the force and torque on the particle are determined. In particular, we predict that the sphere experiences a force orthogonal to its directions of translation and rotation. This “lift” force arises from the nonlinear distortion of the cloud under the combined actions of particle translation and rotation. The lift force is given by . Here, ε is the permittivity of the electrolyte; is the Debye length; and is a negative function that decreases in magnitude with increasing . The lift force implies that an unconstrained particle would follow a curved path; an electrokinetic analog of the inertial Magnus effect. Finally, the implication of the lift force on cross‐streamline migration of an electrophoretic particle in shear flow is discussed.
