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pH

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...

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Updated: May 3, 2026

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

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Published on: July 24, 2015

Unlocking pH-universal charge storage: electrochemically engineered N-doped graphene beyond nanoporosity.

Limin Wang¹, Zhenxiang Chen¹, Yongchun Liu¹

¹Guangxi Key Laboratory of Low Carbon Energy Materials, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin 541004, China.

Journal of Colloid and Interface Science

|August 20, 2025

Summary

This study reveals how nitrogen-doped graphene (N-doped graphene) functions in supercapacitors across different pH levels. It identifies specific functional groups responsible for charge storage in acidic and alkaline conditions, clarifying supercapacitor mechanisms.

Keywords:

Charge-discharge mechanism Electrochemical synthesis In situ FTIR Nitrogen-modified graphene Theoretical calculation

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Area of Science:

Materials Science
Electrochemistry
Nanotechnology

Background:

Carbon-based supercapacitors show great performance but their charge-discharge mechanisms in varying pH are not fully understood.
Decoupling capacitive effects from complex porous structures and ionic channels in these materials is challenging.

Purpose of the Study:

To investigate the pH-dependent charge-discharge mechanisms of carbon-based materials.
To develop a model system for studying these mechanisms across the full pH range.

Main Methods:

Electrochemical synthesis of structure-defined, nanohole-free N-doped graphene (ENG).
In situ Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR) to monitor electrochemical activity.
Theoretical calculations to understand ion adsorption affinities.

Main Results:

Pyridinic N and carboxyl groups in ENG are highly active in acidic media, while hydroxyl groups dominate in alkaline media.
CO bonds show detectable ATR-FTIR peaks in neutral media.
Theoretical calculations confirm stronger H+ adsorption by pyridinic N and carboxyl groups, enhancing acidic performance.

Conclusions:

N-doped graphene (ENG) serves as a robust model for elucidating supercapacitor mechanisms across diverse pH environments.
The study clarifies the distinct roles of different functional groups in charge storage depending on the solution's acidity or alkalinity.