Advertisement

Enhanced supercapacitive performance of MnOx through N2/H2 plasma treatment

  • Shenggao Wang
  • Mingchen Zhou
  • Xujie Wang
  • Yangwu Mao
  • Quanrong Deng
  • Geming WangEmail author
Original Paper
  • 10 Downloads

Abstract

This work relates to the research on the effect of plasma on the performance of manganese oxide. Manganese oxide nanoflakes were prepared through the reaction of KMnO4 and alcohol, and then treated by N2 and N2/H2 plasma. The crystal structure of manganese oxide can be destructed by plasma treatment and manganese oxide become more amorphous and aggregated than those of as-synthesized MnOx, both of which have been proven by XRD and TEM techniques. Results of XPS confirm that the ionic defects and oxygen vacancy are also formed in manganese oxide by plasma. The electrochemical behavior was studied using CV, GCD, and EIS method in 0.5 M Na2SO4 solution. The results show that N2/H2 plasma treatment can fascinate the coexistence of mixed valence of Mn and the formation of oxygen vacancies, reduce the charge-transfer resistance, and then enhance the capacitive performance efficiently.

Keywords

MnOx Plasma Supercapacitors 

Introduction

In recent years, supercapacitors attract considerable attention in the area of energy storage due to its high power density, high energy density, superior cycling stabling, and wide operating temperature range (Zhu et al. 2011; Simon et al. 2014). In terms of the fundamental charge storage mechanisms, supercapacitors can be classified into two types, which are electrical double-layer capacitors (EDLCs) and pseudocapacitors. EDLCs store charge by physical ion adsorption, while pseudocapacitors store charge through fast reversible Faradaic redox reactions on/near the surface of active materials (Zhang et al. 2013a, b; Kang et al. 2015; Ho et al. 2014). Compared with EDLCs, pseudocapacitors have higher specific capacitance and more widespread application. Among all kinds of pseudocapacitors electrode materials, manganese oxides are the most promising materials, because of their low cost, rich resources, high theoretical specific capacitance, and environmental friendliness (Ho et al. 2014; Lee et al. 2015; Jiang et al. 2015). However, the low conductivity and accessible active surface area limit their practical application (Lee et al. 2010; Huang et al. 2015; Shimamoto et al. 2013). To enhance the capacitive performance of MnO2, the good electron conduction and the ion diffusion paths are needed to be obtained (Teng et al. 2010; Li et al. 2015). Carbon nanotubes, graphene and conducting polymer have been used to enhance conductivity and accessible active surface of MnO2 (Pi et al. 2016; Xiao and Xu 2013; zhang et al. 2013b). However, owing to the interface resistance, the MnO2 conductivity resulting from the conductive material can only be enhanced to a limited degree (Wu et al. 2012). To avoid the interface resistance, Kang et al. prepared Au-doped MnO2, which remarkably improved conductivity and capacitive performance of MnO2 (Kang et al. 2013). Liu et al. reported that Co-doped MnO2 exhibited better rate capability and electron transport ability than pure MnO2 (Liu and Yue 2014). Li et al. synthesized Cu-doped hollow-structured MnO2 via the hydrothermal process, which demonstrated 642 mAh/g at the current density of 100 mA/g (Li et al. 2013). On the other hand, oxygen vacancies also played a very important role in enhancing the intrinsic conductivity of MnO2. Zhai et al. prepared hydrogenated MnO2 nanorods by annealing the as-synthesized MnO2 nanorods in H2 at 250 °C for 3 h, and on account of the oxygen vacancies, the hydrogenated MnO2 exhibits high capacitance of 449 F/g at 0.75 m A/cm2 (Zhai et al. 2014). Song et al. claimed that the mixed valence state facilitated the formation of more ionic defects and electronic defects, thus improving the capacitive performance of MnOx (Song et al. 2012).

Plasma modification technology is regarded as an economical and efficient technology applied to various areas, which only works on/near the surface of material (Dorraki et al. 2015; Sahin et al. 2015). Through the plasma modification, the surface structure and valence state of materials can be changed efficiently. It is also expected that plasma treatment can efficiently change the chemical states of Mn in manganese oxide and, thus, significantly enhance its capacitive performance. Therefore, in this paper, we treated MnOx through N2 and N2/H2 plasma, and compared their capacitive performance. Electrochemical measurements showed that, after the N2/H2 plasma treatment, the conductivity and rate capability of MnOx were greatly enhanced, and the relaxation time constant of MnOx was reduced greatly. It shows that N2/H2 plasma treatment is a promising way to enhance the conductivity and capacitive performance of MnOx.

Experimental section

Synthesis and plasma treatment of MnOx

All the chemicals used were of analytical grade and were used without further purification. In a typical experiment, 3 g KMnO4 was dissolved in 200 mL deionized water and stirred with a magnetic stirrer for 30 min to form a homogeneous solution at room temperature. 200 mL ethanol was then added to the solution with constant stirring for 5 h. Later, the precipitate was collected by filtration, and sequentially washed for several times with deionized water and absolute ethanol, and then dried at 60 °C for 12 h. The final product is denoted as MnOx. Afterwards, a given fraction of MnOx (500 mg) was modified by N2/H2 plasma in the microwave plasma generator (2.45 GHz). During the 5 min plasma modification process, the input microwave power was 300 W, and chamber pressure was kept at 0.5 kPa, the N2 and H2 flow rates were kept at 50sccm and 5sccm, respectively. The sample modified by N2/H2 plasma was denoted as MnOx-NH. For comparison, MnOx was also modified by N2 plasma with the same process, which was denoted as MnOx-N.

Characterization and electrochemical measurements

The morphologies and chemical composition of the products were characterized by transmission electron microscopy (TEM, JEM-2010EX, 200 kV), X-ray diffraction (XRD, D8 Brucker), and X-ray photoelectron spectroscopy (XPS, Thermal Scientific INC). Electrochemical studies were performed through a workstation (AMETEK, Princeton perstat4000). The surface and the pore size distribution were evaluated based on the Brunauer–Emmett–Teller (BET) method and the Barret–Joyner–Halenda (BJH) method, respectively. Cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) were carried out by a standard three-electrode cell configuration. The platinum electrode and Ag/AgCl electrode served as counter and reference electrode, respectively. All the electrochemical tests were performed in 0.5 M Na2SO4 solution. The working electrodes were prepared as follows. First, 5 mg material was dissolved into the mixture solution of deionized water (800 μL), alcohol (800 μL), and 5% Nafion (80 μL). Then, it was poured into the ultrasonic vibration for 0.5 h to achieve homogeneous catalyst ink. At last, 5 μL of the ink was dropped on the glass carbon electrode to act as working electrode, and thus, the mass of the active electromaterials was about 0.0149 mg.

Results and discussion

Figure 1 shows the XRD patterns of the as-prepared MnOx and plasma-treated MnOx-NH and MnOx-N. It can be seen that MnOx is poorly crystallized, which may be attributed to the small particle size and amorphous nature property of the sample (Zhang et al. 2015). The three weak diffraction peaks of 2θ at around 12º, 37º, and 66º can be indexed to birnessite-type MnO2 (JCPDS no. 80-1098). It can be deduced from the comparison of XRD patterns that plasma-treated MnOx-N is more poorly crystallized than MnOx, and MnOx-NH is almost amorphous. These results show that the plasma treatment can destruct the crystal structure of manganese oxide and the materials become more amorphous.
Fig. 1

XRD patterns of manganese oxides before and after plasma treatment

Further information on the elemental composition, the valence state of Mn, and the oxygen vacancy in the samples is obtained from XPS measurement. Figure 2a–d shows the Mn valence state in manganese oxide which can be determined by calculating the splitting width of Mn 3 s orbit peak from XPS spectra. From Fig. 2b–d, it is found that the peak splitting width of MnOx, MnOx-N, and MnOx-NH is 4.89 eV, 5.01 eV, and 5.10 eV, respectively. According to the relationship between the peak splitting width and the oxide state of manganese (Toupin et al. 2002; Pang et al. 2015), the average valence state of Mn in MnOx, MnOx-N, and MnOx-NH is about 3.8, 3.6, and 3.4, respectively. MnOx, the as-synthesized manganese oxide, is nearly stoichiometry, and it can react with plasma and tend to form nonstoichiometry oxide. Plasma, especially hydrogen plasma, is beneficial for the reduced reaction of Mn to form ionic defects in manganese oxide. Then, multivalent manganese coexists in plasma-treated samples. Furthermore, the O 1 s peaks in the XPS are believed to be related with the loss of oxygen (oxygen vacancy) in the manganese dioxide samples (Ma et al. 2015; Zhu, et al. 2017). Figure 2e–g shows the asymmetrical O 1 s signals of MnOx, MnOx-N, and MnOx-NH, respectively. All of the three signals can be deconvoluted into two components. The one at binding energy about 529.0 eV is assigned to surface lattice oxygen (OLatt) species, and the other at binding energy about 531.4 eV is related to the surface adsorbed oxygen (OAds) species, which locate at the surface oxygen vacancies of manganese dioxide (Wang, et al. 2012). The estimated OAds:OLatt molar ratios in the MnOx-NH, MnOx-N, and MnOx are 25.8, 16.39, and 13.8% respectively, indicating that the plasma treatment can increase the oxygen vacancy density.
Fig. 2

XPS wide scan survey spectra of MnOx-NH (a) and Mn 3 s core-level spectra of MnOx (b), MnOx-N (c), MnOx-NH (d) and asymmetrical O 1 s signals of MnOx (e), MnOx-N (f), and MnOx-NH (g)

Figure 3 shows the isotherms of MnOx, MnOx-N, and MnOx-NH. The specific surface area of MnOx, MnOx-N, and MnOx-NH are 153 m2/g, 134 m2/g, and 129 m2/g, respectively. Correspondingly, the pores’ volume of MnOx, MnOx-N, and MnOx-NH is 0.582 cm3/g, 0.513 cm3/g, and 0.527 cm3/g, respectively. And the pore size distribution becomes a little broader after plasma treatment.
Fig. 3

a Nitrogen adsorption–desorption isotherms of MnOx, MnOx-N, and MnOx-NH, and b the pore size distribution curves of MnOx, MnOx-N, and MnOx-NH

Figure 4 shows TEM images of MnOx, MnOx-N, and MnOx-NH. It can be seen that most of MnOx fabricated by alcohol reacting with potassium permanganate are flakes. And some manganese oxides are interconnected nanoparticles which create abundant space and, thus, lead to porous nanostructures. After plasma treatment, the manganese oxide flakes break and the interconnected nanoparticles aggregate slightly. The aggregation of manganese oxide particles results in the reduction of specific surface area, which is consistent with the results showed in Fig. 3, but, at the same time, micropores form as flakes break and the interconnected nanoparticles aggregate, especially for MnOx-NH. It is estimated that several factors cause the formation of micropores. During the short-time plasma treatment with the temperature being lower than 100 °C, the interconnection among nanoparticles can resist the aggregation to some extent. Furthermore, because of the reaction between manganese oxide and plasma, gas emits out from manganese oxide and, thus, micropores are formed.
Fig. 4

TEM images of MnOx (a), MnOx-N (b), and MnOx-NH (c)

To evaluate the electrochemical properties of MnOx, MnOx-N, and MnOx-NH, CV, GCD, and EIS are conducted in 0.5 M Na2SO4. Figure 5a, b shows the CV comparison of the three electrodes recorded at a scan rate of 30 mV s−1 and 100 mV s−1, respectively. There are distinctive differences among the three curves, not only in the CV area, but also in the curve shapes. In comparison to MnOx, plasma-treated manganese oxide, especially MnOx-NH, exhibits an obvious pseudocapacitive characteristic, which can be attributed to the presence of low valence Mn ions (Zhai et al. 2014). And the pseudocapacitance of MnOx-NH is evidently bigger than those of the other two. Figure 5c shows the variation of specific capacitance versus scan rate. It can be seen that the specific capacitance decreases gradually with the increasing of scan rate, which can be ascribed to the ion diffusion limitation at high scan rate. The decreases of the specific capacitance of the three samples show that the resistance on the ion diffusion in MnOx-NH is smallest. Furthermore, it is well known that reductions of specific surface area and pores volume are not conducive to the improvement of capacitive performance, including capacitance and rate capability. The specific surface areas of MnOx-NH and MnOx-N are smaller than that of MnOx. However, compared with MnOx, the rate capacitances of MnOx-NH and MnOx-N have been improved dramatically and the specific capacitance is enhanced, especially for MnOx-NH. Although, in comparison with the previous reports (Liu and Yue 2014; Li et al. 2013; Zhai et al. 2014; Song et al. 2012), the specific capacitance of MnOx is a little lower, our results show that the capacitance of MnOx treated by N2 and N2/H2 plasma has been enhanced dramatically. Especially for MnOx-NH, at scan rates of 50 mV/s, 100 mV/s and 200 mV/s, the specific capacitances have increased by 184, 200, and 223%, respectively. Figure 5d shows the galvanostatic charge–discharge curves at the current density of 10 A/g. The discharge time of MnOx-NH is far longer than that of MnOx, which also shows that plasma treatment can efficiently enhance the capacitance of manganese oxide. In addition, the IR drops of the three electrodes are 0.21 V (MnOx), 0.14 V (MnOx-N), and 0.11 V (MnOx-NH), respectively (see Fig. 5e). Plasma-treated manganese oxides have smaller IR drops than MnOx, which shows that the electrical conductivity has been improved by plasma.
Fig. 5

CV curves of three electrodes at scan rates of 30 mV s−1 (a) and 100 mV s−1 (b), variation of specific capacitance of three electrodes at different scan rate (c), comparison of galvanostatic discharge–charge curves of three electrodes collected at a current density of 10 Ag−1 (d), and the comparison of IR drop (e)

To further study the effect of plasma treatment on the electrochemical properties of manganese oxide, electrochemical impedance spectroscopy (EIS) measurement is carried out. According to Fig. 6, all these plots show a semicircle in the high-frequency region arising from the chemical reaction process and straight line in the low-frequency region which is related to the ion diffusion in the electrode materials (Pang et al. 2015). The high-frequency intercepting the X-axis represents the equivalent series resistance (ESR) of electrolyte, intrinsic resistance of active materials, and contact interface resistance between the electrode and electrolyte. And the diameter of the semicircle corresponds to the charge-transfer resistance (Kundu and Liu 2013). Figure 6 reveals that, after N2/H2 plasma treatment, both the equivalent series resistance and the charge-transfer resistance drop dramatically. It confirms that plasma treatment, especially N2/H2 plasma, can efficiently enhance the conductivity of MnOx, which is consistent with the results showed in Fig. 5e. Furthermore, the straight line of MnOx-NH in the low frequency tends to more vertical than that of MnOx, which suggests that the N2/H2 plasma treatment can enhance the capacitive behavior of MnO2 (Miller et al. 2010). Clearly, the largest of straight slope suggests the fastest ions diffuse in MnOx-NH. The fastest ion diffusion rate and the smallest charge-transfer resistance, which can be attributed to coexistence of multivalent Mn and large amounts of oxygen vacancies, lead to the best capacitive performance of MnOx-N. This result is in consistence with Song’s work, in which Song et al. claim that the coexistence of multivalent Mn can facilitate the formation of ionic defects and electronic defects. These defects may accelerate the rate of surface redox reaction, and enhance the transportation of charged species and extend the reaction sites from the surface to the subsurface (Song et al. 2012). Figure 6c represents the variation of the imaginary part of the capacitance with the frequency. The peak of plot represents character frequency (f) and the relaxation time constant (τ = 1/f). The small relaxation time constant means that material can deliver high power (Gu and Wei 2015). It shows that, through N2/H2 plasma treatment, the relaxation time constant is enhanced, which is consistent with the rate capability improvement showed in Fig. 5c.
Fig. 6

Nyquist plots (a), the zoom-in Nyquist plots at high-frequency region (b), and evolution of the imaginary part of the capacitance vs. the frequency (c) of MnOx, MnOx-N, and MnOx-NH

Figure 7 shows the long-term cycling test of MnOx, MnOx-N, and MnOx-NH. The cycling life test is conducted by repeating the CV test between 0 and 1 V at a scan rate of 50 mV/s for 1000 cycles. It can be seen that the capacitance retention value of MnOx-NH maintains better than that of MnOx and MnOx-N, which even increases slightly during the first several hundred cycles. The mechanism of the capacitance increment may be ascribed to the structure reorganization and element redistribution of MnOx-NH during electrochemical oxidation and reduction process (Peng et al. 2013). Moreover, it may also explain the activation process of MnOx-NH that allows the trapped cations to diffuse out gradually and confirms that there are more defects in MnOx-NH (Li et al. 2013).
Fig. 7

The cycle performance of MnOx, MnOx-N and MnOx-NH at a scan rate of 50 mV/s

Conclusion

In summary, plasma treatment can efficiently change the structure of MnOx and valence state of Mn. Compared with as-synthesized MnOx, plasma-treated manganese oxides show better conductivity, rate capability and cycling stability. The better capacitive performance of MnOx-NH can be attributed to the existence of mixed valence of Mn and oxygen vacancies. It shows that plasma treatment is a promising way to enhance the conductivity and capacitive performance of MnOx.

Notes

Acknowledgments

Financial support from National Natural Science Foundation of China (Grants No.: 51272187, 11704288), the Science and Technology Supporting Program of Hubei Province (Grants No.: 2015BAA093, 2013CFA012), and the Scientific Project provided by Wuhan Government (Grants No.: 2016010101010026) was greatly acknowledged.

References

  1. Dorraki N, Safa NN, Jahanfar M, Ghomi H, Siadat SOR (2015) Surface modification of chitosan/PEO nanofibers by air dielectric barrier discharge plasma for acetylcholinesterase immobilization. Appl Surf Sci 349:940–947.  https://doi.org/10.1016/j.apsusc.2015.03.118 CrossRefGoogle Scholar
  2. Gu T, Wei B (2015) Fast and stable redox reactions of MnO2/CNTs hybrid electrodes for dynamically stretchable pseudocapacitors. Nanoscale 7:11626–11632.  https://doi.org/10.1039/C5NR02310F CrossRefGoogle Scholar
  3. Ho MY, Khiew PS, Isa D, Tan TK (2014) A review of metal oxide composite electrode materials for electrochemical capacitors. NANO 9:1430002.  https://doi.org/10.1142/S1793292014300023 CrossRefGoogle Scholar
  4. Huang HJ, Zhang WY, Fu YS, Wang X (2015) Controlled growth of nanostructured MnO2 on carbon nanotubes for high performance electrochemical capacitors. Electrochim Acta 152:480–488.  https://doi.org/10.1016/j.electacta.2014.11.162 CrossRefGoogle Scholar
  5. Jiang Y, Ling XT, Jiao Z, Li L, Ma QL, Wu MH, Chu YL, Zhao B (2015) Flexible of multiwalled carbon nanotubes/manganese dioxide nanoflake textiles for high-performance electrochemical capacitors. Electrochim Acta 153:246–253.  https://doi.org/10.1016/j.electacta.2014.12.023 CrossRefGoogle Scholar
  6. Kang JL, Hirata A, Kang LJ, Zhang XM, Hou Y, Chen LY, Li C, Tujita T, Akagi K, Chen MW (2013) Enhanced supercapacitor performance of MnO2 by atomic doping. Angew Commun 52:1664–1667.  https://doi.org/10.1002/anie.201208993 CrossRefGoogle Scholar
  7. Kang LT, Deng JC, Liu TJ, Cui MW, Zhang XY, Li PY, Liu XG, Liang W (2015) One-step solution combustion synthesis of cobalt-nickel oxides/C/Ni/CNTs nanocomposites as electrochemical capacitors electrode materials. J Power Sources 275:126–135.  https://doi.org/10.1016/j.jpowsour.2014.10.201 CrossRefGoogle Scholar
  8. Kundu M, Liu LF (2013) Direct growth of mesoporous MnO2 nanosheet arrays on nickel foam current collectors for high-performance pseudocapacitors. J Power Sources 243:676–681.  https://doi.org/10.1016/j.jpowsour.2013.06.059 CrossRefGoogle Scholar
  9. Lee SW, Kim JH, Chen S, Hammond PT, Horn YS (2010) Carbon nanotube/manganese oxide ultrathin film electrodes for electrochemical capacitors. ACS Nano 4:3889–3896.  https://doi.org/10.1021/nn100681d CrossRefGoogle Scholar
  10. Lee H, Park SH, Kim SJ, Park YK, Kim BJ, An KH, Ki SJ, Jung SC (2015) Synthesis of manganese oxide/activated carbon composites for supercapacitor application using a liquid phase plasma reduction system. Int J Hydrogen Energy 40:754–759.  https://doi.org/10.1016/j.ijhydene.2014.08.085 CrossRefGoogle Scholar
  11. Li Q, Yin LW, Li ZQ, Wang XK, Qi YX, Ma JY (2013) Copper doped hollow structured manganese oxide mesocrystals with controlled phase structure and morphology as anode materials for lithium ion battery with improved electrochemical performance. Appl Mater Inter 5:10975–10984.  https://doi.org/10.1021/am403215j CrossRefGoogle Scholar
  12. Li CY, Wang SY, Zhang GW, Du ZL, Wang GL, Yang J, Qin XJ, Shao GJ (2015) Three-dimensional crisscross porous manganese oxide/carbon composite networks for high performance supercapacitor electrodes. Electrochim Acta 161:32–39.  https://doi.org/10.1016/j.electacta.2015.02.097 CrossRefGoogle Scholar
  13. Liu B, Yue L (2014) Synthesis and electrochemical properties of Co doped MnO2 framework with nanofibrous structure. Int J Appl Ceram Technol 7:1–6.  https://doi.org/10.1016/j.electacta.2009.10.028 CrossRefGoogle Scholar
  14. Ma YY, Wang RF, Wang H, Key JL, Ji S (2015) Control of MnO2 nanocrystal shape from tremella to nanobelt for enhancement of the oxygen reduction reaction activity. J Power Sources 280:526–532.  https://doi.org/10.1016/j.jpowsour.2015.01.139 CrossRefGoogle Scholar
  15. Miller JR, Outlaw RA, Holloway BC (2010) Graphene double-layer capacitor with ac line-filtering performance. Science 329:1637–1639.  https://doi.org/10.1126/science.1194372 CrossRefGoogle Scholar
  16. Pang MJ, Long GH, Jiang S, Ji Y, Ham W, Wang B, Liu XL, Xi YL (2015) One pot low-temperature growth of hierarchical σ-MnO2 nanosheets on nickel foam for supercapacitor application. Electrochim Acta 161:297–304.  https://doi.org/10.1016/j.electacta.2015.02.089 CrossRefGoogle Scholar
  17. Peng L, Peng X, Liu B, Wu CZ, Xie Y, Yu GH (2013) Ultrathin two-dimensional MnO2/graphene hybrid nanostructures for high-performance, flexible planar supercapacitors. Nano Lett 13:2151–2157.  https://doi.org/10.1021/nl400600x CrossRefGoogle Scholar
  18. Pi XQ, Wang SG, Deng QR, Wang GM, Wang CX, Cui LJ, Chen R, Liu XX (2016) The role of carbon nanotubes on the capacitance of MnO2/CNTs. Russ J Appl Chem 89:1189–1195.  https://doi.org/10.1134/S107042721607020X CrossRefGoogle Scholar
  19. Sahin O, Kaya M, Saka C (2015) Plasma-surface modification on bentonite clay to improve the performance of adsorption of methylene blue. Appl Clay Sci 116:46–53.  https://doi.org/10.1016/j.clay.2015.08.015 CrossRefGoogle Scholar
  20. Shimamoto K, Tadanaga K, Tatsumisago M (2013) All-solid-state electrochemical capacitors using MnO2/carbon nanotube composite electrode. Electrochim Acta 109:651–655.  https://doi.org/10.1016/j.electacta.2013.07.154 CrossRefGoogle Scholar
  21. Simon P, Gogotsi Y, Dunn B (2014) Where do batteries end and supercapacitors begin? Mater Sci 343:1210–1211.  https://doi.org/10.1126/science.1249625 Google Scholar
  22. Song MK, Cheng S, Chen HY, Qin WT, Nam KW, Xu SC, Yang XQ, Bongiorno A, Lee J, Bai JM, Tyson TA, Cho J, Liu ML (2012) Anomalous pseudocapacitive behavior of a nanostructured, mixed-valent manganese oxide film for electrical energy storage. Nano Lett 12:3483–3490.  https://doi.org/10.1021/nl300984y CrossRefGoogle Scholar
  23. Teng F, Santhanagopalan S, Wang Y, Meng DD (2010) In-situ hydrothermal synthesis of three-dimensional MnO2-CNT nanocomposites and their electrochemical properties. J Alloy Comp 499:259–264.  https://doi.org/10.1016/j.jallcom.2010.03.181 CrossRefGoogle Scholar
  24. Toupin M, Brousse T, Belanger D (2002) Influence of microstructure on the charge storage properties of chemically synthesized manganese dioxide. Chem Mater 14:3946–3952.  https://doi.org/10.1021/cm020408q CrossRefGoogle Scholar
  25. Wang F, Dai HX, Deng JG, Bai GM, Ji KM, Liu YX (2012) Manganese oxides with rod-, wire-, tube-, and flower-Like morphologies: highly effective catalysts for the removal of toluene. Environ Sci Technol 46:4034–4041.  https://doi.org/10.1021/es204038j CrossRefGoogle Scholar
  26. Wu ZS, Zhou G, Yin LC, Ren WC, Li F, Cheng HM (2012) Graphene/metal oxide composite electrode materials for energy storage. Nano Energy 1:107–131.  https://doi.org/10.1016/j.nanoen.2011.11.001 CrossRefGoogle Scholar
  27. Xiao F, Xu Y (2013) Electrochemical co-deposition and characterization of MnO2/SWNT composite for supercapacitor application. J Mater Sci: Mater Electron 24:1913–1920.  https://doi.org/10.1007/s10854-012-1034-9 Google Scholar
  28. Zhai T, Xie SL, Yu MG, Fang PP, Liang CL, Lu XH, Tong YX (2014) Oxygen vacancies enhancing capacitive properties of MnO2 nanorods for wearable asymmetric supercapacitors. Nano Energy 8:255–263.  https://doi.org/10.1016/j.nanoen.2014.06.013 CrossRefGoogle Scholar
  29. Zhang LL, Gu Y, Zhao XS (2013a) Advanced porous carbon electrodes for electrochemical capacitors. J Mater Chem A 1:9395–9408.  https://doi.org/10.1039/C3TA11114H CrossRefGoogle Scholar
  30. Zhang W, Mu B, Wang A (2013b) Preparation of manganese dioxide/multiwalled carbon nanotubes hybrid hollow microspheres via layer-by-layer assembly for supercapacitor. J Mater Sci 48:7581–7586.  https://doi.org/10.1007/s10853-013-7574-4 CrossRefGoogle Scholar
  31. Zhang YF, Zhang CX, Huang GX, Xing BL, Duan YL (2015) Synthesis and capacitive properties of manganese oxide nanoparticles dispersed on hierarchical porous carbons. Electrochim Acta 166:107–116.  https://doi.org/10.1016/j.electacta.2015.03.073 CrossRefGoogle Scholar
  32. Zhu YW, Murali S, Stoller MD, Ganesh KJ, Cai W, Ferreira PJ, Pirkle A, Wallace RM, Cychosz KA, Thommes M, Su D, Stach EA, Ruoff RS (2011) Carbon-based supercapacitors produced by activation of grapheme. Science 332:1537–1541.  https://doi.org/10.1126/science.1200770 CrossRefGoogle Scholar
  33. Zhu GX, Zhu JG, Jiang WJ, Zhang ZJ, Wang J, Zhu YF, Zhang QF (2017) Surface oxygen vacancy induced-MnO2 nanofiber for highly efficient ozone elimination. Appl Catal B-Environ 209:729–737.  https://doi.org/10.1016/j.apcatb.2017.02.068 CrossRefGoogle Scholar

Copyright information

© Institute of Chemistry, Slovak Academy of Sciences 2019

Authors and Affiliations

  • Shenggao Wang
    • 1
  • Mingchen Zhou
    • 1
  • Xujie Wang
    • 1
  • Yangwu Mao
    • 1
  • Quanrong Deng
    • 1
  • Geming Wang
    • 1
    Email author
  1. 1.Provincial Key Laboratory of Plasma Chemistry and Advanced MaterialsWuhan Institute of TechnologyWuhanChina

Personalised recommendations