Optimizing oxygen substituents of a carbon cathode for improved capacitive behavior in ethanol-based zinc-ion capacitors
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摘要: 锌离子电容器(ZICs)具有能量密度高、倍率性能好、循环寿命长、成本低等优点,近年来得到了广泛的研究。在碳基阴极表面引入氧官能团是提高水系ZICs电容性能的有效策略。然而,氧官能团的存在是否有利于提高乙醇(EtOH)基ZICs的电容性能,目前还没有被深入研究。本文采用硝酸氧化和进一步热处理的方法对阴极活性炭表面的氧官能团进行了优化。在ZnCl2/EtOH电解液中,优化后的样品在电流密度为1 A g−1时比电容达到195 F g−1,比未改性的样品 (125 F g−1)提高了56%。同时,ZICs也表现出良好的循环稳定性,在3 A g−1下的稳定循环次数超过16000次,并且保持100%的库仑效率。这是因为氧官能团,特别是羧基和酯基(―COO)的存在,为Zn2+氧化还原反应提供了丰富的电化学活性位点。因此,本研究通过优化氧官能团增强了炭阴极的电容性能,并为EtOH基ZICs的商业应用提供了研究基础。Abstract: Zinc ion capacitors (ZICs) have been widely studied in recent years due to their high energy density, excellent rate capability, long cycling life and low cost. The incorporation of oxygen functional groups (OFGs) on the surface of the carbon-based cathodes is an effective strategy for improving the capacitive performance of aqueous ZICs. However, whether their presence helps improve the capacitance of ethanol (EtOH)-based ZICs has not been investigated. In this work, a combination of nitric acid oxidation and thermal treatment was used to regulate the OFGs on the activated surface of the carbon cathode. The optimized sample had a high specific capacitance of 195 F g−1 at 1 A g−1 using ZnCl2/EtOH as the electrolyte, i.e., a 56% increase compared to an unmodified cathode (125 F g−1). ZICs also shown excellent stability for more than 16 000 cycles at 3 A g−1, while maintaining 100% coulombic efficiency. This significantly improved performance is attributed to the presence of OFGs, especially carboxyl and ester groups, which provide abundant electrochemical active sites for redox reaction with the zinc ions. This study reports a significant improvement in the specific capacitance of carbon cathodes for commercial EtOH-based ZIC systems.
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Key words:
- Zinc-ion capacitors /
- Oxygen functional groups /
- Ethanol /
- Activated carbon /
- Specific capacitance
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Figure 3. (a) CV curves at different scan rates for (b) AC and (c) AC-O-500, (d) CV comparison of AC and AC-O-500 at 1 mV s−1, (e, f) contribution ratio of the capacitive capacities, (g) contribution ratios, (h) b values in both the charge and discharge processes of AC and AC-O-500, (i) nyquist plots of AC and AC-O-500
Table 1. Structural parameters of AC, AC-O, AC-O-400, AC-O-500 and AC-O-600
Samples SBETa/(m2 g−1) SMicrob/(m2 g−1) VTotalc/(cm3 g−1) VMicrod/(cm3 g−1) AC 1751.16 1500.97 0.904 0.734 AC-O 1240.78 1093.44 0.734 0.521 AC-O-400 1221.51 1001.25 0.684 0.498 AC-O-500 1286.62 1020.91 0.699 0.519 AC-O-600 1386.31 1086.03 0.741 0.558 Note: a-BET (Brunauer-Emmett-Teller) surface area. b-Micropore specific surface area obtained from the QSDFT method. c-Single-point total pore volume at p/p0 = 0.995. d-Micropore volume obtained from the QSDFT method. Table 2. Analysis of the fitted O 1s peaks of the OFGs on the AC samples from XPS spectra
Samples C=O (531.3 eV)/% OH (532.3 eV)/% C―O―C (533.3 eV)/% COO (534.3 eV)/% AC 1.33 2.69 1.34 0.74 AC-O 2.23 6.10 3.33 1.50 AC-O-400 1.93 2.73 5.52 1.77 AC-O-500 1.53 2.23 4.72 1.93 AC-O-600 1.28 1.86 3.65 1.25 -
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Supporting Information2023-0030.pdf