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Related Concept Videos

The Electrical Double Layer01:30

The Electrical Double Layer

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In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...
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The Debye–Hückel Theory of Electrolyte Solutions01:27

The Debye–Hückel Theory of Electrolyte Solutions

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The Debye–Hückel theory, established by Peter Debye and Erich Hückel in 1923, is a fundamental concept in physical chemistry. It provides an understanding of the behavior of strong electrolytes in solution, particularly explaining their deviations from ideal behavior.The theory is based on Coulombic interactions (the attraction or repulsion between charged particles) between ions in solution. In an ionic solution, oppositely charged ions tend to attract each other. This means...
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Electrochemical Systems01:24

Electrochemical Systems

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Electrochemical systems provide a fascinating insight into the dynamic interplay of charged species within various phases. One notable example is the interaction between a membrane permeable to K⁺ ions but not to Cl⁻ ions, separating an aqueous KCl solution from pure water. As K⁺ ions diffuse through the membrane, they generate net charges on each phase, leading to a potential difference between them.Similarly, when a piece of Zn is immersed in an aqueous ZnSO₄ solution,...
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Processes at Electrodes01:30

Processes at Electrodes

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The electrode interacts with ions in the electrolyte solution at its interface. The rate of oxidation and reduction depends on the speed at which electrons can transfer through this interface. As ions attach to or leave the electrode surface, the electrode acquires a charge, and an electrical potential forms across the interface, making the process more difficult to reach equilibrium. The charge on the electrode affects the local ion concentrations in the solution, though thermal motion...
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Theory of Strong Electrolytes01:23

Theory of Strong Electrolytes

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The interionic forces of the strong electrolytes depend on the solvent's dielectric constant, which is the ability of a solvent to store electrical energy, based on its polarizability. and the solution's concentration. In high-dielectric solvents and in dilute solutions, weak electrostatic forces keep ions apart. However, in low-dielectric solvents or concentrated solutions, stronger interionic forces may cause ions to pair up as ionic doublets despite being fully ionized. The theory of strong...
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Ion Exchange01:17

Ion Exchange

1.4K
Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or...
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Updated: Feb 28, 2026

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone
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Equilibria model for pH variations and ion adsorption in capacitive deionization electrodes.

Ali Hemmatifar1, Diego I Oyarzun1, James W Palko1

  • 1Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, USA.

Water Research
|June 17, 2017
PubMed
Summary

This study introduces a new model for capacitive deionization (CDI) that accounts for surface charge variations due to acid-base equilibria in porous electrodes. The model accurately predicts ion adsorption and enhances understanding of surface functional group effects on salt removal efficiency.

Keywords:
Activated carbonCapacitive deionizationSurface functional groupsTitrationWeak electrolytespH

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Area of Science:

  • Electrochemistry
  • Materials Science
  • Environmental Engineering

Background:

  • Capacitive deionization (CDI) relies on ion adsorption at porous electrodes.
  • Current CDI models often assume fixed surface charge, neglecting acid-base equilibria.
  • Surface functional groups significantly impact CDI performance.

Purpose of the Study:

  • To develop an advanced CDI model incorporating weak electrolyte acid-base equilibria.
  • To investigate how pH and surface functional groups influence ion adsorption.
  • To introduce a 'chemical charge efficiency' parameter for salt removal.

Main Methods:

  • Coupling the modified Donnan (mD) model with acid-base equilibria theory.
  • Developing a model where surface charge density varies with pH and equilibrium constants.
  • Validating the model with titration experiments on activated carbon cloth (ACC).
  • Utilizing ICP-MS and ion chromatography for ion concentration analysis.

Main Results:

  • The model demonstrates preferential cation/anion adsorption based on surface group acidity/basicity.
  • A new 'chemical charge efficiency' parameter quantifies functional group contribution to salt removal.
  • Experimental validation with ACC shows excellent agreement with model predictions.
  • Model accurately predicts pH changes due to ACC interaction.

Conclusions:

  • The developed model accurately captures ion adsorption influenced by surface charge equilibria in CDI.
  • Surface functional groups play a crucial role in salt removal efficiency.
  • The model provides a framework for designing improved porous electrodes for CDI.