Nitrogen-doped carbon quantum dots embedded polyoxomolybdate frameworks toward high-performance supercapacitor

• Published in: Journal of energy storage 2024-09, Vol.98, p.113015, Article 113015
• Main Authors: Hasan, Md. Akib, Islam, Md. Mominul
• Format: Article
• Language: English
• Subjects: Carbon quantum dots; Lemon juice; Nitrogen-doped carbon quantum dots; Polyoxometalate; Supercapacitor
• ISSN: 2352-152X
• DOI: 10.1016/j.est.2024.113015

In the pursuit of high energy supercapacitor electrodes, we have engineered an exceptional pseudocapacitive material with phenomenal energy density and cycle stability based on lemon-derived carbon quantum dots (CQDs) and polyoxomolybdate (H3PMo12O40, POMo). Herein, we demonstrate that the CQDs and nitrogen doped CQDs (N-CQDs) can be employed as effective nano-enhancers to surge up the electrochemical supercapacitive performances of POMo. These QDs were developed by the hydrothermal carbonization of pulp free lemon juice. POMo, a metal-inorganic framework of Mo and O with P at the center, was synthesized via simple precipitation method from (NH4)2MoO4 and NH4H2PO4 in acidic condition. The binary composites of POMo with CQDs and N-CQDs were prepared via simply dispersing them under ultrasonication. All of the materials were characterized using state-of-the-art techniques for molecular and electrochemical analysis. The as-prepared composites delivered a specific capacitance (Csp) of 660 F g−1 at 0.3 A g−1 for POMo-10 % CQDs, whereas an exceptionally high Csp of 1960 F g−1 at 0.5 A g−1 for POMo-10 % N-CQDs in 0.5 M H2SO4 (aq) which are ~35 and ~120 times higher than that of the pristine POMo, respectively. The N-CQDs based composites have superior charging-discharging tolerance with nearly 96 % initial Csp-retention after 3000 cycles at 20.0 A g−1. These QDs leverage the development of comprehensive conductive networks within the POMo matrix, allowing facile charge transfer and ion migration throughout POMo with substantial kinetics enhancement. This, in turn, facilitates the transport and storage of electrolyte ions within the intricate and deeply branched micropores. The novel electrode materials based on polyoxometalates and lemon derived oxygen-enriched nitrogen-doped CQDs presented in this study opens up new possibilities for improving capacitive and rate performances in high energy supercapacitors. [Display omitted] •Synthesizing green light-emitting, nitrogen-doped CQDs from lemon juice via hydrothermal-carbonization•Embedding nitrogen-doped CQDs into polyoxometalate electron and proton sponges•Fabricating an acid-tolerant supercapacitor with an enhanced capacitance of 1960 F g-1 at 0.5 A g-1•Obtaining remarkable energy cycle robustness of 96% initial Csp-retention after 3000 cycles at 20.0 A g-1.