How Buffers Resist Electrochemical Reaction-Induced pH Shift under a Rotating Disk Electrode Configuration

Area of Science:

• Electrochemistry
• Physical Chemistry
• Chemical Engineering

Background:

• Electrochemical reactions can alter the pH at the electrode-electrolyte interface (pHs).
• Limited buffer capacity in solutions exacerbates pHs changes.
• Buffer pairs are crucial for stabilizing pHs during electrochemical processes.

Purpose of the Study:

• To investigate the quantitative relationship between interfacial pH (pHs), bulk pH (pHb), buffer properties, and reaction rate.
• To develop predictive models for pHs shifts in electrochemical systems.
• To provide guidelines for selecting appropriate buffer systems for electrochemical applications.

Main Methods:

• Numerical simulations of a model electrochemical reaction (H2X ⇄ 2H+ + X + 2e-) under rotating disk electrode conditions.
• Analysis of pHs changes across a wide range of bulk pH (0-14).
• Evaluation of buffer pairs with varying pKa values and concentrations.

Main Results:

• Established quantitative relationships between pHs, pHb, buffer pKa, buffer concentration, and reaction current density.
• Generated diagrams illustrating pHs and pH shifts (ΔpH) as functions of pHb and current density.
• Defined maximum allowable current density (jmax) for acceptable pHs deviations (ΔpH < 0.2).

Conclusions:

• The study provides predictive diagrams (j-pHs) for estimating interfacial pH and ΔpH without direct measurement.
• jmax-pHb plots serve as a practical guide for selecting buffer pairs to mitigate pH shifts.
• Understanding and controlling pHs is critical for optimizing electrochemical reaction efficiency and selectivity.