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Related Concept Videos

Acid–Base Equilibria: Activity-Based Definition of pH01:10

Acid–Base Equilibria: Activity-Based Definition of pH

563
For an ideal solution, the pH is defined as the negative logarithm of the hydrogen ion concentration. For a non-ideal solution, an accurate measurement of the pH must consider the negative logarithm of the hydrogen ion activity rather than concentration. In such a solution, the pH can be more accurately defined as the negative logarithm of a product of the hydrogen ion concentration and its activity coefficient.
In solutions of very low ionic strength—for example, pure water—the...
563
Titration of a Strong Acid with a Strong Base01:23

Titration of a Strong Acid with a Strong Base

5.2K
During the titration of a strong acid with a strong base, pH calculations are primarily based on the concentration of residual hydronium or hydroxide ions. Initially, a strong acid like hydrochloric acid fully dissociates, creating hydronium and chloride ions, resulting in a low pH. The addition of a strong base like sodium hydroxide alters the concentration of hydronium ions by neutralizing them. As more base is added, the pH gradually increases. At the equivalence point, all hydronium ions...
5.2K
pH Scale02:41

pH Scale

68.6K
Hydronium and hydroxide ions are present both in pure water and in all aqueous solutions, and their concentrations are inversely proportional as determined by the ion product of water (Kw). The concentrations of these ions in a solution are often critical determinants of the solution’s properties and the chemical behaviors of its other solutes. Two different solutions can differ in their hydronium or hydroxide ion concentrations by a million, billion, or even trillion times. A common means of...
68.6K
pH01:24

pH

133.4K
The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. However, the extensive range of hydronium ion concentrations present in water-based solutions makes measuring pH in moles cumbersome. Therefore, a pH scale was developed to convert moles of hydronium ions into the negative logarithm of the hydronium...
133.4K
Mixtures of Acids03:27

Mixtures of Acids

19.6K
The pH of a solution containing an acid can be determined using its acid dissociation constant and its initial concentration. If a solution contains two different acids, then its pH can be determined using one of several methods depending upon the relative strength of the acids and their dissociation constants.
A Mixture of a Strong Acid and a Weak Acid
In a mixture of a strong acid and a weak acid, the strong acid dissociates completely and becomes a source of almost all the hydronium ions...
19.6K
Henderson-Hasselbalch Equation02:48

Henderson-Hasselbalch Equation

68.7K
The ionization-constant expression for a solution of a weak acid can be written as:
68.7K

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Insights into the pH effect on hydrogen electrocatalysis.

Wen-Gang Cui1, Fan Gao1, Guoquan Na1

  • 1Institute of Science and Technology for New Energy, Xi'an Technological University, Xi'an, 710021, P. R. China.

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Understanding the pH effect on hydrogen reactions is key for better fuel cells and water electrolyzers. This review explores theories and catalyst designs to overcome sluggish alkaline kinetics for a sustainable energy future.

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Area of Science:

  • Electrochemistry
  • Materials Science
  • Energy Conversion and Storage

Background:

  • Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are vital for energy technologies.
  • These reactions exhibit significantly slower kinetics in alkaline media compared to acidic media.
  • A fundamental understanding of this pH-dependent kinetics is crucial for advancing energy devices.

Purpose of the Study:

  • To provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis.
  • To discuss experimental observations, underlying principles, and catalyst design strategies.
  • To address the current debates and future research directions in alkaline HER/HOR.

Main Methods:

  • Review of experimental findings and theoretical models (HBE, bifunctional, pzfc, 2B theories).
  • Analysis of activity descriptors across various electrolytes and catalyst surfaces.
  • Highlighting catalyst design principles and electrolyte optimization for improved alkaline kinetics.

Main Results:

  • The review synthesizes current knowledge on the pH effect in hydrogen electrocatalysis.
  • It critically evaluates various theories explaining the observed kinetics.
  • It identifies strategies for enhancing alkaline HER/HOR performance through rational catalyst design.

Conclusions:

  • A deeper molecular-level understanding of the pH effect is essential for developing efficient catalysts.
  • Optimizing catalysts and electrolytes is key to overcoming sluggish kinetics in alkaline media.
  • This work aims to guide the development of cost-effective alkaline water electrolyzers and fuel cells.