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

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.