The effect of low‐defected carboxylic acid functional group–rich carbon nanotube–doped electrode on the performance of aqueous vanadium redox flow battery

Abstract

Summary Modified (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO)‐mediated oxidation (MTMO) is introduced to fabricate low‐defected carboxylic acid functional group–rich carbon nanotube (TEMPO‐CNT) through facile and eco‐friendly chemical preparation. Due to the MTMO, the O=C‐O portion (18.2%), representing the amount of active site to vanadium ion redox reaction (VIRR), reaches the nearly same with conventionally acid‐treated CNT (AT‐CNT, 18.9%). However, the intensity ratio of D to G band of TEMPO‐CNT is measured lower value (1.14) than that of AT‐CNT (1.29) in Raman spectra, showing the MTMO is the better strategy to functionalize carboxylic groups on CNT with the uniform structure and low‐defected feature. Furthermore, when the TEMPO‐CNT is utilized for the catalyst for VIRR, the catalytic activity increases to 2.11 (negolyte) and 2.03 (posolyte) times compared to AT‐CNT, and the reversibility of VIRR is also improved. These results attribute to the 41.6% lower charge transfer resistance than AT‐CNT, demonstrating that the low‐defected CNT structure of TEMPO‐CNT induced a facile electron transfer, resulting in the high catalytic performance. With that, the energy efficiency (EE) and discharge capacity of vanadium redox flow battery (VRFB) adopting TEMPO‐CNT display 58.8% and 16.8 Ah L−1 even at high current density (250 mA cm−2), whereas those of AT‐CNT are only 52.3% and 6.8 Ah L−1. Regarding long‐term stability, the TEMPO‐CNT and AT‐CNT preserved 98.8% and 91.4% of retention rate in EE at 200 mA cm−2 for 200 cycles, respectively, indicating that the MTMO is the promising option to fabricate the catalyst to use in the practical VRFB.

Asymmetric Chemical Potential Activated Nanointerfacial Electric Field for Efficient Vanadium Redox Flow Batteries

“…By comparison, it can be deduced that the performance strengthening unambiguously stems from the accelerated reaction kinetics of VO 2+ /VO 2 + redox couple due to the accelerator-like nanointerfacial E -fields (Figure h). Finally, we prove that the nanointerfacial E -fields liberated on the multilevel substrate network bestows outstanding flow battery capabilities, beating representative targets in recent literature with regard to the key current density and energy efficiency performance metrics, as demonstrated in Figure i and Table S9. ,− …”

Controlled Construction of a N-Doped Carbon Nanotube Network Endows Carbon Felt with Superior Performances for High-Rate Vanadium Flow Batteries

“…(a) Cycling performance and (b) capacity retention of the VFB using NCNT@CF-10 electrodes at 200 mA cm –2 . (c) Comparison of energy efficiency between the NCNT@CF-10 and carbon-based nanomaterial-modified electrodes reported in the open literature. ,,,,,,,− …”

“…Pristine CNTs have demonstrated remarkable capabilities in enhancing redox reversibility for V 2+ /V 3+ and VO 2+ /VO 2 + couples, primarily attributed to fast electron transport performance. , Furthermore, to make full use of their substantial specific surface area, significant efforts have been devoted to modifying CNTs to enhance the redox kinetics. These modifications typically involve functional group grafting, − heteroatom doping (nitrogen, phosphate, and sulfur), and nanomaterial compositing . Typically, the modified CNTs are bonded to the electrode surface to yield composite electrodes using organic binders, such as Nafion and dimethylformamide.…”

Two-dimensional polymeric cobalt phthalocyanine synthesized by microwave irradiation and its use for continuous glucose monitoring

“…The anodic peak current near 0.35 V was used to plot the relationship between the peak current and the scan rate for all electrodes. As a result, the peak current density of all three electrodes increased proportionally to the scan rate, indicating that the two-step reaction is surfacecontrolled [49].…”