全钒氧化还原液流电池用石墨毡电极的分步氧化活化

石墨毡电极是组成钒电池的关键材料,其较低的电化学活性是造成钒电池功率密度较低的关键因素之一. 本论文采用一种简便的石墨毡电极分步氧化活化法,先将石墨毡在高锰酸钾溶液中进行氧化,后置于活化溶液中激发其反应活性. 通过对处理后的石墨毡进行循环伏安、交流阻抗测试、XPS以及SEM表征,发现氧化时间和活化溶液组成是影响电极性能的因素,在本文中,先经过3天氧化时间,后在配比为3:1的活化溶液中处理的电极,较其他方法处理的电极,电荷传递电阻明显降低,其与溶液之间的接触电阻最低,为7.33 Ω·cm ²,氧化还原峰值比更接近于1,有效提高了反应的活性与可逆性,经X射线光电子能谱分析发现性能提高的原因与表面含氧官能团数目增加有关. 单电池性能测试结果进一步证实,利用该方法处理的石墨毡为电极的单电池,较未经处理的电池相比性能更优,有更高的放电容量和能量效率,在100 mA·cm ^-2电流密度下,能量效率较未处理电极高出7.47%. 与热处理法、酸处理法及电化学氧化法相比较,该方法不需要辅助设备,不消耗能源.     

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Developing robust oxygen electrocatalyst with high-performance is very significant for practical rechargeable Zn-air battery.We report herein the preparation of three-dimensional continuous nanocarbon network composed of interconnected nitrogen-doped carbon nanotubes and its application as oxygen electrocatalysis in rechargeable Zn-air battery.Except the excellent electrochemical bifunctionality,this carbon nanotube matrix also delivers an impressive battery performance.Specifically,an opencircuit voltage of 1.50 V as well as a high power density of 220 m W cm^-2 with remarkable cycling stability for 1600 h is achieved in the rechargeable Zn-air battery.The study not only provides an efficient bifunctional oxygen electrocatalyst but more importantly may pave significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies.     

Novel catalytic effects of Mn3O4 for all vanadium redox flow batteries

A new approach for enhancing the electrochemical performance of carbon felt electrodes by employing non-precious metal oxides is designed. The outstanding electro-catalytic activity and mechanical stability of Mn(3)O(4) are advantageous in facilitating the redox reaction of vanadium ions, leading to efficient operation of a vanadium redox flow battery.     

全钒液流电池碳电极材料的研究进展

近年来,全钒液流电池作为一种大规模储能装置,其电极材料得到了广泛的研究,并且获得了一定的进展.本文简述了全钒液流电池对电极材料的要求,综述了其电极材料的研究进展,重点介绍了碳电极及其改性方面的工作,并对其电极材料的发展趋势进行了展望.     

Hydrothermal ammoniated treatment of PAN-graphite felt for vanadium redox flow battery

A novel method of hydrothermal ammoniated treatment on the polyacrylonitrile (PAN)-based graphite felt for vanadium redox flow battery was developed. The graphite felt was treated in a Teflon-lined stainless steel autoclave for different time at 180 °C. The content of nitrogen in the PAN graphite felt changed from 3.803% to 5.367% by adjusting treatment time to 15 h in ammonia solution, while FT-IR results indicated that nitrogenous groups were introduced. The electrochemical properties of these graphite felts were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, as well as cell charge and discharge tests. The energy efficiency of the treated graphite felt reached 85% at a current density of 20 mA/cm². The corresponding coulombic efficiency and voltage efficiency were 95.3% and 75.1%, respectively. The improvement of the electrochemical properties for the treated graphite felt might be attributed to the increase of polar nitrogenous groups of carbon fiber surface, which facilitated charge transfer between electrode and vanadium ions.     

Modified multiwalled carbon nanotubes as an electrode reaction catalyst for an all vanadium redox flow battery

Different modified multiwalled carbon nanotubes (MWCNTs) are prepared by heat treatments in the air and in the H₂SO₄?+?HNO₃ (1:1) mixed acids which are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Brunaur–Emmett–Teller, and cyclic voltammetry measurements. The results show the physicochemical properties of MWCNTs change significantly after these different modification processes, especially the electrochemical catalytic activity towards the VO₂ ⁺/VO²⁺ and V³⁺/V²⁺ redox pairs. The MWCNTs treated in the air at 600 °C for 30 min shows better electrochemical performances for the VO₂ ⁺/VO²⁺ redox reactions (58.8 and ?32.4 μA for the oxidation and reduction peaks at 10 mV?s^?1, respectively) than any other samples. Compared with the V³⁺/V²⁺ redox couple, the VO₂ ^+/VO²⁺ redox reactions are more easily affected by the physicochemical property changes of the MWCNTs. The enhanced electrochemical catalytic activity of the modified MWCNTs is not only related to the surface oxygen content, but also to the specific surface area, conductivity and the unique structure variations of the MWCNTs. The investigation demonstrated that the modified MWCNTs have a promising future application in the vanadium redox flow battery.     

Detrimental role of hydrogen evolution and its temperature-dependent impact on the performance of vanadium redox flow batteries

This paper addresses the damaging role of the parasitic hydrogen evolution reaction(HER) in the negative half-cell of a vanadium redox flow battery(VRFB) on state-of-the-art carbon felt electrodes at different temperatures. It was found that increasing the temperature resulted in a better catalytic performance for both the positive and negative half-cell reactions. In addition, increasing the temperature significantly enhanced the undesired HER at the negative side. Operating the VRFB cell at higher temperature led to a decrease in the coulombic efficiency attributed to the higher hydrogen production. More pronounced hydrogen production caused an oxidation on the surface of the carbon fibers and a degradation of the electrode as indicated from scanning electron microscopy and X-ray photoelectron spectroscopy measurements. This observed degradation results in fading of the overall performance of the vanadium redox flow battery over time.     

NiO/ZnO Composite Derived Metal-Organic Framework as Advanced Electrode Materials for Zinc Hybrid Redox Flow Battery

NiO/ZnO composite derived metal-organic framework (MOF) is used as to modify carbon felt (CF) via a conventional solid-state reaction followed by ultrasonication. The prepared electrode material is used in zinc-hybrid redox flow batteries (RFBs) due to their high redox activity of Zn²⁺/Zn. The electrochemical performance of composite modified CF and pre-treated CF was studied by cyclic voltammetry (CV) in 0.5 M aqueous zinc chloride with 5 M potassium hydroxide solutions showed clear confirmation for enhanced electrocatalytic activity. The unique porous structure of NiO/ZnO-derived MOF with increased surface area improves the battery behavior significantlyThe peak current ratio for the as-prepared material is about 3 times higher than that of the pre-treated CF due to more active sites. Zinc-based RFB with modified CF electrode exhibited better electrochemical performance with voltage efficiency (VE, 88 %), which is higher than true redox flow batteries.     

High electro-catalytic graphite felt/Mn O2composite electrodes for vanadium redox flow batteries

A mild and simple synthesis process for large-scale vanadium redox flow batteries(VRFBs)energy storage systems is desirable.A graphite felt/Mn O_2(GF-MNO)composite electrode with excellent electrocatalytic activity towards VO~(2+)/VO_2~+redox couples in a VRFB was synthesized by a one-step hydrothermal process.The resulting GF-MNO electrodes possess improved electrochemical kinetic reversibility of the vanadium redox reactions compared to pristine GF electrodes,and the corresponding energy efficiency and discharge capacity at 150 m A cm~(-2)are increased by 12.5%and 40%,respectively.The discharge capacity is maintained at 4.8 A h L~(-1)at the ultrahigh current density of 250 m A cm~(-2).Above all,80%of the energy efficiency of the GF-MNO composite electrodes is retained after 120 charge-discharge cycles at 150 m A cm~(-2).Furthermore,these electrodes demonstrated that more evenly distributed catalytic active sites were obtained from the Mn O_2particles under acidic conditions.The proposed synthetic route is facile,and the raw materials are low cost and environmentally friendly.Therefore,these novel GF-MNO electrodes hold great promise in large-scale vanadium redox flow battery energy storage systems.     

Three‐dimensional Nitrogen‐Doped Reduced Graphene Oxide/Carbon Nanotube Composite Catalysts for Vanadium Flow Batteries

The development of vanadium redox flow battery is limited by the sluggish kinetics of the reaction, especially the cathodic VO₂⁺/VO²⁺ redox couples. Therefore, it is vital to develop new electrocatalysts with enhanced activity to improve the battery performance. Herein, we synthesized the hydrogel precursor by a facile hydrothermal method. After the following carbonization, nitrogen‐doped reduced graphene oxide/carbon nanotube composite was obtained. By virtue of the large surface area and good conductivity, which are ensured by the unique hybrid structure, as well as the proper nitrogen doping, the as‐prepared composite presents enhanced catalytic performance toward the VO₂⁺/VO²⁺ redox reaction. We also demonstrated the composite with carbon nanotube loading of 2 mg/mL exhibits the highest activity and remarkable stability in aqueous solution due to the strong synergy between reduced graphene oxide and carbon nanotubes, indicating that this composite might show promising applications in vanadium redox flow battery.     

Evolution of Vanadium Redox Flow Battery in Electrode

The vanadium redox flow battery (VRFB) is a highly regarded technology for large-scale energy storage due to its outstanding features, such as scalability, efficiency, long lifespan, and site independence. This paper provides a comprehensive analysis of its performance in carbon-based electrodes, along with a comprehensive review of the system‘s principles and mechanisms. It discusses potential applications, recent industrial involvement, and economic factors associated with VRFB technology. The study also covers the latest advancements in VRFB electrodes, including electrode surface modification and electrocatalyst materials, and highlights their effects on the VRFB system‘s performance. Additionally, the potential of two-dimensional material MXene to enhance electrode performance is evaluated, and the author concludes that MXenes offer significant advantages for use in high-power VRFB at a low cost. Finally, the paper reviews the challenges and future development of VRFB technology.     

Electrochemistry of polystyrene intercalated vertically aligned single- and double-walled carbon nanotubes on gold electrodes

Electrochemical electrodes incorporating double- and single-walled carbon nanotubes (CNTs) were fabricated on cysteamine modified flat gold substrates. Through covalent coupling of the amine end groups with carboxyl functionalized CNTs, a dense forest of vertically aligned CNTs was produced. To these a 30 nm thick insulating polystyrene layer was spin coated, resulting in exposure of the uppermost carbon nanotube ends. The electrochemical performance of each electrode was then determined using the redox probe ruthenium hexaamine. Once surrounded by polymer, the double-walled CNTs (DWCNTs) showed an improved electron transfer rate, compared to the single-walled electrode. This improvement was attributed to the protection of the electronic properties of the inner wall of the DWCNT during the chemical modification and suggests that DWCNTs may offer a useful alternative to SWCNTs in future electrochemical sensors and biosensors.     

The catalytic effect of bismuth for VO_2~+/VO~(2+) and V~(3+)/V~(2+) redox couples in vanadium flow batteries

The effect of bismuth(Bi) for both VO_2~+/VO2+ and V~(3+)/V~(2+) redox couples in vanadium flow batteries(VFBs) has been investigated by directly introducing Bi on the surface of carbon felt(CF).The results show that Bi has no catalytic effect for VO_2~+/VO2+ redox couple.During the first charge process,Bi is oxidized to Bi~(3+)(never return back to Bi metal in the subsequent cycles) due to the low standard redox potential of 0.308 V(vs.SHE) for Bi3+/Bi redox couple compared with VO_2+/VO2+ redox couple and Bi~(3+)exhibit no(or neglectable) electro-catalytic activity.Additionally,the relationship between Bi loading and electrochemical activity for V~(3+)/V~(2+) redox couple was studied in detail.2 wt%Bi-modified carbon felt(2%-BiCF) exhibits the highest electrochemical activity.Using it as negative electrode,a high energy efficiency(EE) of 79.0%can be achieved at a high current density of 160mA/cm~2,which is 5.5%higher than the pristine one.Moreover,the electrolyte utilization ratio is also increased by more than 30%.Even the cell operated at 140mA/cm2 for over 300 cycles,the EE can reach 80.9%without obvious fluctuation and attenuation,suggesting excellent catalytic activity and electrochemical stability in VFBs.     

A systematic study of the electrochemical determination of hydrogen peroxide at single-walled carbon nanotube ensemble networks

The electrochemical detection of one of the most sought after analytical targets has been studied at single-walled carbon nanotube ensemble networks, which are electrically wired via an underlying electrode substrate. A range of parameters and their effect on the electro–analytical detection of hydrogen peroxide have been explored which includes heterogeneity, role of the underlying electrode, electrode pre-treatment and analytical performance. This work provides researches with an overall view of the various parameters, which may affect the electro–analytical detection of hydrogen peroxide at native carbon nanotubes before modification with electro–catalytic materials allowing the assignment of the true origin of electro–catalysis to be properly assigned.     

锂硫电池复合正极研究进展

锂硫电池因其超高的理论能量密度被视为极具前景的下一代电化学储能体系,其中高比容量的硫正极提供了锂硫电池的能量密度优势并直接决定了电池的实际性能。经过数十年的发展,最具前景的硫正极体系分别是硫碳复合（S/C）正极和硫化聚丙烯腈（SPAN）正极。本文系统综述了S/C正极和SPAN正极的最新研究进展。首先,简要介绍了两种正极的工作原理并进行了比较。S/C正极发生固-液-固多相转化反应,充放电表现为双平台特征。与之相比,SPAN正极发生固-固反应,充放电曲线为单平台。然后,对两种正极所面临的挑战和目前报道的优化策略进行了系统的分析与讨论。对于S/C正极,主要调控策略包括电极结构修饰、电催化剂设计与辅助氧化还原介体调控;对于SPAN正极,主要调控策略包括电极结构设计、电极形貌调控、杂原子掺杂和外源性氧化还原介体调控。最后,在电池尺度上对S/C正极和SPAN正极进行了综合比较,并对基于S/C正极和SPAN正极的锂硫电池在未来所面对的机遇与挑战进行了展望。     

全钒液流电池磺化石墨烯/Nafion复合膜的研究

本文通过磺化石墨烯对Nafion膜进行改性,研究了磺化石墨烯/Nafion复合膜（GRS-Nafion复合膜）的吸水率、电阻率和钒离子迁移数. 结果表明,经磺化石墨烯改性之后,GRS-Nafion复合膜的面电阻和钒离子渗透率显著降低. 全钒液流电池的测试结果表明,GRS-Nafion复合膜有着更加优异的电化学性能,展示出GRS-Nafion复合膜在液流电池中的应用潜力.     

Hydrous manganese oxide/carbon nanotube composite electrodes for electrochemical capacitors

A novel type of composite electrode based on hydrous manganese oxide and a single-walled carbon nanotube has been prepared and used in electrochemical capacitors. Cyclic voltammetry, galvanostatic charging/discharging tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of hydrous manganese oxide and single-walled carbon nanotube. For comparison, the performance of pure hydrous manganese oxide and pure carbon nanotubes was also studied. In this way, the composite electrode with a 6:4 ratio of hydrous manganese oxide to carbon nanotube was found to be the most promising active material for an electrochemical capacitor, which shows both good capacitance and power characteristics.     

High electro-catalytic graphite felt/MnO<Subscript>2</Subscript> composite electrodes for vanadium redox flow batteries

A mild and simple synthesis process for large-scale vanadium redox flow batteries (VRFBs) energy storage systems is desirable. A graphite felt/MnO₂ (GF-MNO) composite electrode with excellent electrocatalytic activity towards VO²⁺/VO₂⁺ redox couples in a VRFB was synthesized by a one-step hydrothermal process. The resulting GF-MNO electrodes possess improved electrochemical kinetic reversibility of the vanadium redox reactions compared to pristine GF electrodes, and the corresponding energy efficiency and discharge capacity at 150 mA cm^?2 are increased by 12.5% and 40%, respectively. The discharge capacity is maintained at 4.8 A h L^?1 at the ultrahigh current density of 250 mA cm^?2. Above all, 80% of the energy efficiency of the GFMNO composite electrodes is retained after 120 charge-discharge cycles at 150 mA cm^?2. Furthermore, these electrodes demonstrated that more evenly distributed catalytic active sites were obtained from the MnO₂ particles under acidic conditions. The proposed synthetic route is facile, and the raw materials are low cost and environmentally friendly. Therefore, these novel GFMNO electrodes hold great promise in large-scale vanadium redox flow battery energy storage systems.     

Mesoporous carbon nitride loaded with Pt nanoparticles as a bifunctional air electrode for rechargeable lithium-air battery

A composite comprised of oxygen reduction reaction (ORR) catalyst and oxygen evolution reaction (OER) catalyst was designed and applied as a bifunctional electrocatalyst for the air electrode of the lithium-air battery. The ordered mesoporous carbon nitride (MCN) prepared by a nano hard-templating approach displayed a surface area as high as 648 m² g^?1 and a large pore volume of 0.7 cm³ g^?1 and acted as both the ORR catalyst and the support for the in situ-formed OER catalyst of Pt particles with a diameter of 3–4 nm. The electrochemical performances of the electrode were examined in a solid-state lithium-air cell structured as Li/LATP-based electrolyte/cathode, which demonstrated a higher round-trip efficiency and lower overpotential compared with the Pt@AB and MCN electrodes. The combination of the OER and ORR catalysts is proved as an effective way to improve the performance of lithium-air batteries.     

水热氧化改性碳纸电极在全钒氧化还原电池中的应用

为了提高钒氧化还原电池电极的活性,在180°C下将碳纸电极与过氧化氢的硫酸溶液置于有聚四氟乙烯内衬的不锈钢反应釜中进行不同时间的水热酸氧化处理.水的接触角测试表明,随着处理时间从6h调整至18h,处理前后碳纸电极的接触角也从120.0°降低至100.8°,尤其是经过12h处理的样品的接触角最小,这说明在此条件下处理过的碳纸的亲水性得到了提高.而傅里叶变换红外测试表明,羰基和羧基等含氧基团被成功地引入到了碳纸电极中.使用扫描电镜,循环伏安,电化学阻抗以及充放电技术分别检测了处理前后样品的表面形貌及电化学性能.V(IV)/V(V)氧化还原电对在这些处理过的样品上表现出较大的活性.用处理12h的碳纸电极组装的单电池性能优异,在30mA·cm-2的电流密度下能量效率达到了80%,相应的电流效率和电压效率分别为96%和84%.