Combined Effect of Nitrogen‐ and Oxygen‐Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

TLDR

The study systematically investigates how nitrogen‑ and oxygen‑containing functional groups, introduced by melamine and urea treatments on coconut‑shell‑derived activated carbon, influence electrochemical performance in 1 M H₂SO₄ supercapacitors. The authors prepared the carbon by high‑temperature treatment, then characterized its surface chemistry with elemental analysis, Boehm and potentiometric titrations, X‑ray photoelectron spectroscopy, and measured textural properties via N₂ and CO₂ sorption. They found that the nitrogen precursor and pre‑existing surface groups dictate nitrogen incorporation, with pseudocapacitance from oxygen and nitrogen groups in pores larger than 10 Å, 5–6 Å pores favoring double‑layer formation, quaternary and pyridinic‑N‑oxides enhancing high‑current capacitance, and pyrrolic and pyridinic nitrogen together with quinone oxygen being the most critical functional groups for energy storage.

Abstract

Abstract Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen‐ and oxygen‐containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H 2 SO 4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X‐ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea‐ and melamine‐treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 Å. On the other hand, pores between 5 Å and 6 Å are most effective in a double‐layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic‐N‐oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen.