Mechanochemically Assisted Microwave-Induced Plasma Synthesis of a N‑Doped Graphitic Porous Carbon-Based Aqueous Symmetric Supercapacitor with Ultrahigh Volumetric Capacitance and Energy Density

In the realm of affordable and yet efficient energy storage devices required for future portable electronic gadgets and electric vehicles, supercapacitors (SCs) have immense potential; however, the prime bottleneck is the low volumetric capacitance and energy density caused by the sluggish reaction kinetics and a limited potential window (<1.2 V) in aqueous electrolytes. Therefore, to address this challenge, we aim to design suitable biomass-derived nitrogen (N)-doped highly porous graphitic carbon (HP-NGC) via a mechanochemically assisted microwave plasma-induced quick synthesis process to deliver high volumetric capacitance and energy density. Detailed characterization of the developed electrode materials revealed that the structural and functional properties are highly influenced by the crucial role of mechanochemical treatment carried out just before carbonization through microwave irradiation under N2 plasma. HP-NGC produces an almost 32% higher surface area (820 m2 g–1) than the surface area (620 m2 g–1) of N-doped graphitic carbon (NGC) prepared without mechanochemical treatment. Moreover, HP-NGC shows more N doping (IDIG∼1.01) than NGC (where N doping is 1.1 atom % and IDIG is ∼0.98), which significantly affects their electrochemical storage properties. The HP-NGC electrode exhibited ∼145% higher volumetric capacitance (840 F cm–3) and energy density (168 Wh L–1) than the volumetric capacitance (308 F cm–3) and energy density (61.5 Wh L–1) of the NGC electrode within a wide potential window of 1.2 V measured at 0.5 A g–1 in 6 M KOH. Finally, the assembled aqueous symmetric device (HP-NGC//HP-NGC) made of HP-NGC electrodes exhibits a volumetric capacitance of 630 F cm–3 with excellent rate performance (∼81% capacitance retained even after increasing the current density by 10 times), high-energy density of 32 Wh L–1, and power density of 640 W L–1 at 0.5 A g–1, which is higher than those of many reported porous carbon-based symmetric devices, making it a promising candidate for commercial applications

Genetic map of pMET1 and comparison to plasmid pCRY and chromosomal elements.

<p>A. The genetic maps of pMET1 and pCRY are compared showing the homologous regions. The arrows indicate genes locations and orientation. Genes with different functions are shown with different colors and if the genes in the different structures shown are homologus they are represented with the same colors. Yellow: mobilization; green: replication and partition; red: antibiotic resistance; purple: virB/pilX-like; blue: transposition; grey: unknown. Since pCRY is smaller than pMET1, to represent it in circular form a dotted line was added to fill the gap. Solid line represents non-homologous DNA. B. Comparison of a pMET1 region with chromosomal HPIs or ICEs is shown using a linearized version of the plasmid. The HPIs shown are those from <i>E. coli</i> ECOR31 (HPI_ECOR31) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001800#pone.0001800-Schubert1" target="_blank">[43]</a>, <i>K. pneumoniae</i> NTUH-K2044 (ICE_Kp1) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001800#pone.0001800-Lin1" target="_blank">[44]</a>, and <i>Y. pestis</i> KIM (HPI_Yp)<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001800#pone.0001800-Schubert1" target="_blank">[43]</a>. The diagram shows the HP core regions, which are not at scale and are represented as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001800#pone.0001800-Schubert1" target="_blank">[43]</a>, and the RB-HPIs. The sequence described in this manuscript has been deposited in GenBank, accession number is EU383016.</p

Replication region of pMET1.

<p>A. The bar shows a genetic map of the pMET1 replication region and the GC content plot generated using a window size of 100 bp on top. Recombinant clones were obtained by inserting the indicated fragments into pCR2.1 or ligated to the pUC4K <i>aph</i> cassette. The ability to be maintained in <i>E. coli</i> C2110 (a <i>polA</i> mutant) of the recombinant plasmids made using pCR2.1 as vector is indicated to the right by a + or − sign. The ability to generate kanamycin resistant colonies in <i>E. coli</i> TOP10 of the indicated fragments when ligated to the <i>aph</i> cassette from pUC4K is also represented by a + or − sign. B. BLASTP comparison of the amino acid sequences of the putative RepA proteins from pMET1 and pCRY.</p