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

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 H2SO4 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.

Nitrogen-containing chitosan-based carbon as an electrode material for high-performance supercapacitors

“…At low scan rates, NCh2 exhibits the highest capacity value, which agrees with the highest total content of nitrogen-and oxygen-containing functional groups on its surface, based on the XPS results ( Table 2). In addition, this sample possesses the highest content of pyridinic-N (N-6), pyrrolic/pyridonic-N (N-5), and quinone-O (O-I) groups, to whom the pseudocapacitive effect is attributed [33,34]. Hydroxyl groups were also found to contribute to pseudocapacitance [35].…”

Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors

“…It has previously been reported that retaining some amount of oxygen moieties enhances the capacitive performance of graphene material in addition to the presence of nitrogen groups. 40 The partially reduced nature of our N-rGO ensures the presence of some residual oxygen functional groups which provide another pseudo-capacitive contribution to the total material capacitance. The capacitance per unit area reported here is approximately twice that reported previously using the same technique for nonfunctionalised liquid phase exfoliated graphene electrodes.…”

Comparison of surface and bulk nitrogen modification in highly porous carbon for enhanced supercapacitors

“…A second peak is also present in each sample, centered around 531.5 eV, which may be attributed to oxygen double bonded to carbon as a quinone type group [23,51]. A very small third peak is seen at approximately 535.4 eV, which may correspond to chemisorbed oxygen or water [23,51]. After adding the hexamine coating to carbon, the relative amount of C−O as compared to C=O decreases.…”

“…A summary of each of the different peaks and their percent contribution is shown in Table 3. The detailed scans of O1s peak show that each of the three samples has a peak centering at approximately 533.1 eV which can be attributed to oxygen single bonded to carbon in the form of phenol and/or ether groups [23,51]. A second peak is also present in each sample, centered around 531.5 eV, which may be attributed to oxygen double bonded to carbon as a quinone type group [23,51].…”

“…The detailed scans of O1s peak show that each of the three samples has a peak centering at approximately 533.1 eV which can be attributed to oxygen single bonded to carbon in the form of phenol and/or ether groups [23,51]. A second peak is also present in each sample, centered around 531.5 eV, which may be attributed to oxygen double bonded to carbon as a quinone type group [23,51]. A very small third peak is seen at approximately 535.4 eV, which may correspond to chemisorbed oxygen or water [23,51].…”