Flow-type membraneless hydrogen peroxide fuel cell (HPFC) having high power density is fabricated using buckypaper (BP) based electrodes and eddy-inducing cell structure to use low concentrated H2O2 fuel. Benefiting from...
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.
A facile and inexpensive method of fabricating a myoglobin-mimic nanostructure is introduced by evaluating the influence of temperature conditions on the axial coordination between the Fe core of hemin and amine of polyethyleneimine (PEI). Through the high-temperature (100 C) synthesis condition, more hemin molecules are strongly attached to the carbon nanotube and PEI composite owing to the amide bond formation, whereas the energy distribution of hemin is deformed, and the electrical connection is improved by the coordination of axial ligands when the catalyst is synthesized on a lower temperature (25 C). Benefiting from the high concentration of axial ligands, the onset potential is positively shifted by 0.258 V, and the highest current density (155.43 μA cm À2 ) is observed with 10 mM H 2 O 2 under physiological conditions. These phenomena occur because of the different hydrogen peroxide reduction reaction (HPRR) mechanisms and the overpotential stemming from the effect of the axial ligand, which induces the lowest catalytic and charge transfer resistance for HPRR at 51 and 820 Ω cm À2 , respectively. In the polarization curves measured using a 3D printed membraneless flow-type fuel cell, the maximum power density reaches 129.0 μW cm À2 with 0.340 V of opencircuit voltage, respectively, which offers the best performance among the reported studies for the membraneless hydrogen peroxide fuel cells driving under physiological conditions so far.
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