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. 2021 Oct 12;6(42):27994–28003. doi: 10.1021/acsomega.1c03863

Preparation of Graphene Oxide/La2Ti2O7 Composites with Enhanced Electrochemical Performances for Supercapacitors

Munan Lu †, Yi Cao §,*, Yufeng Xue †, Wenfeng Qiu †,‡,*
PMCID: PMC8552325  PMID: 34722999

Abstract

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A series of graphene oxide (GO)/lanthanum titanate (La2Ti2O7, LTO) fiber composites were prepared through a hydrothermal method. The LTO fibers were homogeneously dispersed between the GO sheets. The structure and micromorphology of the GO/LTO composites were systematically studied. The composite exhibited a high specific capacitance of 900.6 F g–1 at a current density of 1 A g–1 in the 1 M H2SO4 and 10 wt % sucrose aqueous solution as the electrolyte. With the extended potential window of 1.8 V, the fabricated asymmetric supercapacitor device delivered a maximum energy density of 94.0 Wh kg–1 at a power density of 750.1 W kg–1. The GO/LTO composites could be promising materials for energy storage.

1. Introduction

With the rapid development of portable and wearable devices, there is an urgent need to seek high-performance electrical energy systems.1 In the last decade, supercapacitors have attracted much attention due to their high stability, long cycle life, and high power density.2−5 However, supercapacitors still suffer from low energy density and limited working voltage.2,6,7 In general, according to their energy storage mechanisms, supercapacitors are cataloged into two main types, the electric double-layer capacitors (EDLCs) and pseudocapacitors. Previous studies have shown that the EDLCs possessed a better voltage range, while the pseudocapacitors exhibited better specific capacitance.7,8 Hence, the advantages of EDLCs and pseudocapacitors can be combined to improve the comprehensive performance of supercapacitor devices.

Various electrode materials have been used for supercapacitors; among them, graphene has been investigated as a competitive EDLC electrode material.9−12 With a large theoretical surface area of 2630 m2 g–1, it possesses high electrical conductivity and theoretical gravimetric capacitance of 550 F g–1.13,14 However, the specific capacitance of graphene-based electrodes was reported to be only 150–230 F g–1 in the inorganic electrolytes.15,16 Because the restacking of graphene sheets strongly decreases the accessible surface area,13,14,17,18 the performance of graphene in the energy storage devices was not as excellent as the theoretical calculation. Many transition-metal oxides (TMOs) have been studied for their good pseudocapacitance properties. It has been reported that the electrical performance of other carbon materials was enhanced by doping TMOs, such as mesoporous carbon,19,20 carbon nanofibers,9,21,22 and carbon nanosheets.23,24 It is feasible to increase the energy storage properties by the combined use of TMOs and graphene.8,25,26 Various groups have reported on the combined use of graphene and TMOs to overcome the drawbacks in the electrochemical properties.

Zhang et al.27 prepared the graphene/La2O3 nanocomposite by a reflux process. It showed a high specific capacitance of 156.25 F g–1 at a current density of 0.1 A g–1. Bokhari et al.28 synthesized a hybrid composite of reduced graphene oxide (rGO)/TiO2 with 334 F g–1 at 0.1 A g–1. Yue et al.29 reported a hydrothermal method to develop TiO2 nanowire/rGO nanocomposites and a high capacitance of 202.5 F·g–1 at 1 A·g–1 was obtained. Cheng et al.30 synthesized amorphous Co2SiO4 nanobelts by a template method. The optimum specific capacitance of Co2SiO4/GO composites was 511 F g–1 at 0.5 A g–1 with 84% retention after 10 000 cycles. Wang et al.31 prepared a cyanometallic framework-derived hierarchical Co3O4-NiO/graphene foam by a solution immersion and subsequent annealing treatment. The electrode showed a specific capacitance of 766 F g–1 at 1 A g–1. Isacfranklin et al.32 presented the SmCoO3/rGO hybrid supercapacitors employing a solvothermal route and the maximum specific capacity was obtained as 30.8 mAh g–1 for 1 A g–1.

However, most of the works were based on graphene and rGO, rather than GO, as the matrix of the composites for electrode materials. Although GO suffered from low conductivity and low capacity, the wettability of GO was better, which helps the interaction with aqueous electrolytes.10,33 GO has rich oxygen functional groups, which exhibit great electroactivity and could facilitate the electrochemical reaction kinetics.34 Both the preparation and application of GO are easier and more convenient for mass production.33,34 With the improved electrochemical properties of GO, it could be a promising high-performance electrode material for industry. In addition, the loading ratio of the TMOs in previous reports was over 60 wt %, which could have ignored the contribution of graphene itself. Our group35,36 previously reported an electrospun lanthanum titanate (La2Ti2O7, LTO) system, which exhibited a high areal capacitance of 806.2 mF cm–2 at 2 mA cm–2 with a potential window of 2.1 V in the aqueous electrolyte. Such LTO fibers have great potential to develop a composite system to promote better electrochemical properties for GO. The introduction of LTO fibers may provide more pseudocapacity to the GO matrix, and the layer restacking would be reduced, which may increase the EDL capacity as well.

In this paper, a series of GO/LTO composites were successfully prepared by the hydrothermal method. The LTO fiber loading was lower than those in other reports, while the composite exhibited excellent electrochemical properties. To investigate the effect of adding LTO fibers, the composites with various contents of LTO were characterized by several methods. The electrochemical properties of the GO/LTO composites were studied in detail.

2. Results and Discussion

GO, LTO, and GO/LTO composites of different proportions were investigated by X-ray diffraction (XRD) measurements. Their XRD patterns are shown in Figure 1, the main diffraction peaks at 2θ = 21–33° were indexed to the orientations of the (210), (400), (212), (410), and (210) planes of LTO.35 For the pristine GO sample, the intense peak at 2θ = 10.9° corresponded to the GO (001) plane, indicating the successful synthesis of GO. The patterns of GO/LTO-8 and GO/LTO-10 revealed a main peak at 2θ = 10.9° and several characteristic peaks at 2θ = 21–33°, which proved the hybrid of GO and LTO. However, due to the low content ratio of the fibers, no obvious characteristic peaks belonging to LTO were detected in the GO/LTO-2 and GO/LTO-5 samples. In general, the modification of the samples was not sufficient with the low ratio of the LTO fibers. Therefore, 8 wt % of LTO fibers was selected for the robust composition in this research.

Figure 1.

Figure 1

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XRD patterns of GO, LTO, and GO/LTO composites.

To further investigate the effects of LTO on GO, the morphologies of GO and GO/LTO composites were observed through scanning electron microscopy (SEM). As shown in Figure 2, the LTO fibers were observed as red circles. The short LTO fibers could be detected homogeneously separated in the GO matrix in the GO/LTO-5 and GO/LTO-8 samples (Figure 2a,b). The diameter of the fiber was about 100 nm. The length of the LTO fibers was ∼5 μm due to the high ultrasonic energy during the mixing. The fibers were not only on the surface of the GO sheets but also between the GO sheets. The interlayer LTO fibers were also observed from the edge of the GO/LTO-8 sample as shown in Figure 2c. However, the LTO fibers tended to aggregate when the content of the LTO fibers was over 10 wt % (shown in Figure 2d). This inhomogeneous separation would lead to the defects of the graphene sheets, which caused the low electronic conductivity. Therefore, the ratio of 8 wt % would be the best proportion.

Figure 2.

Figure 2

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SEM images: (a) GO/LTO-5; (b) GO/LTO-8; (c) GO/LTO-8 edge; (d) GO/LTO-10; and (e) energy dispersive spectrometer (EDS) mappings of GO/LTO-8.

Furthermore, EDS elemental mappings of the GO/LTO-8 composite are measured and shown in Figure 2e, indicating the homogeneous distribution of La, Ti, and O elements on the GO sheets. It was confirmed from the spectrum that the LTO fibers aligned homogeneously between GO sheets.

To determine the best ratio of LTO fibers, the electrochemical properties of GO, LTO, and GO/LTO composites were tested and compared. The GO sample was hydrothermally treated as the same route of the composite. The samples with various proportions of LTO were prepared as the working electrodes and measured in the 1 M H2SO4 electrolyte through the cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) methods. The CV curves of GO, LTO, and GO/LTO composites at the scan rates of 100 mV s–1 are shown in Figure 3, and the specific capacitances of the samples displayed in Table 1 are calculated from the GCD curves (Figure S1) at the current density of 1 A g–1 by eq 1. With the mixing of LTO fibers, the potential window of the composites was extended to 1.6 V, larger than that of pristine GO (1.0 V) and LTO (1.1 V) in the 1 M H2SO4 electrolyte. The specific capacitance of the composite samples also increased significantly upon the hybridization of LTO fibers.

Figure 3.

Figure 3

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CV curves of GO, LTO, and GO/LTO composites at 100 mV s–1.

Table 1. Electrochemical Properties of GO, LTO, and GO/LTO Composites.

sample potential window (V) specific capacitance (F g–1)
GO 1.0 107.3
LTO 1.1 ∼185.7
GO/LTO-2 1.6 440.8
GO/LTO-5 1.6 602.5
GO/LTO-8 1.6 769.4
GO/LTO-10 1.6 403.4
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Among them, the GO/LTO-8 composite showed the highest specific capacitance of 769.4 F g–1. There were two possible reasons for the excellent electrochemical properties of the GO/LTO composites. First, the introduction of LTO fibers increased the distance between GO sheets, which enhanced the ability of the electrode to absorb charges from the electrolyte. Both the EDL capacitance and pseudocapacitance benefitted from the larger layer distance. Second, it is possible that the LTO fibers, which possessed high pseudocapacitance, increased the specific capacitance of the GO/LTO composites. However, when the mixing ratio was over 10 wt %, the electrochemical properties dropped significantly. As shown in the SEM image of GO/LTO-10 (Figure 2d), it was possible that the aggregated LTO fibers led to poor separation, which decreased the interaction between the GO matrix and the LTO fibers. In addition, the LTO with the poor electric conductivity also increased the charge transfer resistance at the aggregation spot, which decreased the ion transmission. In summary, the potential window of GO was expanded by the introduction of LTO fibers, and the specific capacitance was also enhanced. In this study, 8 wt % of LTO fibers was the best, which was supported by both XRD and SEM results.

2.1. Energy Storage Mechanism

Since the GO/LTO composites possessed high specific capacitance and large potential window, the structure change affected by the LTO fibers for the composite was investigated to demonstrate the energy storage mechanism. The pseudocapacitance of GO was explained to originate from electrochemical reactions37

2.1.

while the energy storage mechanism of the LTO was considered as oxygen intercalation. The oxygen ions on the surface can be transferred through the LTO lattice, and they can be absorbed by the oxygen vacancies in bulk.35 The LTO redox reaction was described as

2.1.

Therefore, it can be demonstrated that the oxygen groups of GO, functioning as ladders, enable the in situ formation of Ti(OH)3+ attaching on the surfaces of GO sheets. The electrical capacity was significantly increased due the accelerated progress. It was demonstrated that GO showed low potential window because of the decomposition of the oxygen-containing function groups.38 The loss of oxygen-containing function groups was possibly decreased by the inserted LTO fibers. The potential window of the LTO fibers can reach 2.1 V in the Na2SO4 aqueous electrolyte, indicating the possible large potential window when hybridized with GO.35 The restacking of GO sheets was also reduced by introducing LTO fibers, providing more surfaces for the redox reactions. To reveal the structural change, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectrometer (XPS) were conducted to further explore the GO/LTO-8 composite.

The surface structures of GO and GO/LTO-8 composites were analyzed by FT-IR spectroscopy. As shown in the spectrum of GO in Figure 4, there were a series of absorption peaks belonging to different organic groups. The peak at 1618 cm–1 corresponded to the stretching vibrations of C=C double bonds. The broad peak centered at 3245 cm–1 was the stretching and vibration of the O–H bond. The absorption peaks at 3410, 1722, and 1418 cm–1 were aligned to the carboxyl functional groups (COOH). And the peaks located at 1260 and 1049 cm–1 were corresponding to the epoxy functional groups (C–O–C). Compared to GO, the spectrum of GO/LTO-8 showed stronger absorption peaks at 1262 and 1053 cm–1 corresponding to C–O and C–O–C stretching vibrations. Moreover, the peaks before 900 cm–1 were aligned to LTO fibers,39 indicating that LTO fibers were bonded to the GO matrix. All of these results suggested that the LTO fibers and GO sheets were successfully combined through the hydrothermal process and promoted the stronger C–O interaction in the GO/LTO-8 composite than that in the pristine GO.

Figure 4.

Figure 4

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FT-IR spectra of GO and GO/LTO-8.

In this research, the energy storage mechanism needed more evidence. Therefore, the composition of the GO/LTO-8 composite was studied by the XPS analysis. In Figure 5a, the characteristic peaks of C 1s, O 1s, La 3d, and Ti 2p are detected in the spectrum. The details of the O 1s spectrum of pristine GO and GO/LTO-8 are displayed in Figure 5b. By the software fitting, the O 1s peak of GO can be split into three major peaks located at 531.6, 532.7, and 533.3 eV, corresponding to the chemisorbed oxygen (O–), C–O/–OH, and C=O. Compared to GO, the O 1s peak of the GO/LTO-8 sample can be split into four peaks; apart from the peaks mentioned in GO, there was the peak located at 532.2eV corresponding to the lattice oxygen (O2–). The C=O peak was stronger than the pristine GO, which indicated that the composite had a stronger C–O interaction. In addition, the spin–orbit characteristic peaks of La 3d and Ti 2p are shown in Figure 5c,d. It was confirmed from the XPS spectrum that the LTO fibers were successfully attached to the GO sheets, and as a result, the composite was able to provide rich oxygen sites.

Figure 5.

Figure 5

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XPS spectra of GO/LTO-8: (a) full scan of the composite; (b) O 1s; (c) La 3d; and (d) Ti 2p.

To further confirm that the enhancement was relied on the rich oxygen sites, a graphite/LTO-8 sample was prepared and tested. The graphite was known to lack the oxygen sites. Hence, the graphite/LTO-8 sample should show more unsatisfactory electrochemical performance than the GO/LTO-8 sample. Calculating from the CV and GCD curves displayed in Figure S2, the specific capacitance of the graphite/LTO-8 sample was only 59.3 F g–1 at 1 A g–1 and the potential window of 1.6 V. Therefore, it can be concluded that the enhancement of the electrochemical properties of the GO/LTO composites was attributed to the increase of rich oxygen sites through the introduction of LTO fibers through the hydrothermal process.

2.2. Electrochemical Performance of GO/LTO-8

The electrochemical performance of GO/LTO-8 was further analyzed. From the previous reports,40,41 the electrodes could have better performance in the water-in-salt electrolyte systems. The ultrahigh concentrated solution helps to reduce the electrolysis of water, which could increase the potential window of the electrode as well as the specific capacitance. The GO/LTO-8 composite was further tested in the 1 M H2SO4 and 10 wt % sucrose aqueous electrolyte. Figure 6a shows the CV curves of GO/LTO-8 obtained at various scan rates from 10 to 100 mV s–1. The CV curves were in the quasi-rectangle with a series of redox peaks, indicating that the energy storage mechanism of GO/LTO was the combination of EDL capacitance and pseudocapacitance. Compared to the sample tested in 1 M H2SO4 electrolyte, the potential window was further extended to 1.8 V. The curves at low scan rates showed two pairs of redox peaks corresponding to GO and LTO redox reactions. The shapes of CV profiles changed slightly with the increase of scan rate, suggesting good Coulombic efficiency.

Figure 6.

Figure 6

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(a) CV curves of GO/LTO-8 at various scan rates from 10 to 100 mV s–1; (b) GCD curves of GO/LTO-8 at different current densities from 1 to 10 A g–1; (c) specific capacitance of GO/LTO-8 at different current densities; and (d) electrochemical impedance spectroscopy (EIS) measurement of GO/LTO-8.

Figure 6b presents the GCD curves of GO/LTO-8 at different current densities from 1 to 10 A g–1 in the 1 M H2SO4 and 10 wt % sucrose electrolyte. The GCD curves were not asymmetric during the charge and discharge processes due to the redox reactions of the electrode, which matched the results from the CV curves. Furthermore, the specific capacitance was calculated by eq 1 based on the GCD curves (shown in Figure 6b). The maximum specific capacitance of the GO/LTO-8 electrode was 900.6 F g–1 at the current density of 1 A g–1. Although the specific capacitance dropped to 38% (344.4 F g–1) of the maximum capacitance at 10 A g–1, it was still higher than that of the pristine GO. As the potential window of the composites was enhanced by introducing LTO fibers, the low content of LTO fibers led to the voltage drop at the extended potential window.

The GO/LTO-8 electrode was further examined through the electrochemical impedance spectroscopy (EIS) measurement. Figure 6d presents the EIS curve of the GO/LTO-8 composite in the frequency range from 100 kHz to 0.01 Hz. The EIS curve in the Nyquist plots showed a semicircle in the high-frequency range and a straight line in the low-frequency range. The EIS data was fitted by Z-View software, and the equivalent circuit is inserted in Figure 6d. According to the curve-fitting result, the solution resistance (Rs) was 1.66 Ω and the charge transfer resistance (Rct) between the electrolyte solution and the electrode was 0.1 Ω. The composite had low Rct, which promoted the improvement of electrochemical properties.

In addition, the electrochemical properties of the GO/LTO composite were compared with some recent works concerning graphene (shown in Table 2).27,30,31,42−46 The content ratio of the GO/LTO composite was significantly lower than the previous electrode active materials. However, the GO/LTO composite delivered an excellent specific capacitance among these different composites. The potential window of the GO/LTO composite was also higher than most of the works. Therefore, the GO/LTO composite showed the competitive electrochemical properties with a relatively low content.

Table 2. Comparison of the GO/LTO Composite with Recent Works.

material specific capacitance potential window (V) loading content (wt %) reference
GO/LTO 900.6 F g–1 at 1 A g–1 1.8 8 this work
ZnO@rGO 949 F g–1 at 1 A g–1 1.5 60 (45)
Co3O4–NiO/graphene foam 766 F g–1 at 1 A g–1 0.4 63 (31)
rGO/Mn3O4 438.7 F g–1 at 0.3 A g–1 1.6 71 (46)
3D-graphene/MnO2 333.4 F g–1 at 0.2 A g–1 1.0 75 (42)
Co2SiO4 nanobelts/GO 511 F g–1 at 0.5 A g–1 0.65 91 (30)
rGO/La2O3 156.25 F g–1 at 0.1 A g–1 1.0 91 (27)
CeO2/Ce2O3/rGO 1027 F g–1 at 1 A g–1 0.45 93 (43)
NbOF/GO 599 F g–1 at 0.5 A g–1 0.6 95 (44)
FeOF/GO 459 F g–1 at 0.2 A g–1 0.52 95 (44)
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The asymmetric supercapacitor devices were fabricated to investigate the practical applications. The device GO/LTO//GO/LTO was assembled with GO/LTO-8 electrodes as described. The electrochemical properties of the device were tested though CV and GCD methods. As shown in Figure 7a, the CV curves maintained a similar shape at different scan rates, indicating that the device could be stably applied in various conditions. The specific capacitance of the supercapacitor was calculated by the GCD curves. The maximum specific capacitance was 208.8 F g–1 at 1 A g–1. The energy density and power density of the device were also calculated by eqs 2 and 3. The device delivered a maximum energy density of 94.0 Wh kg–1 at the power density of 750.1 W kg–1, and the energy density was 15.6 Wh kg–1 at the high power density of 7506 W kg–1. The Ragone plot is presented in Figure 7c. Compared to some recent reported works42,46−50 (shown in Figure 7c), the GO/LTO asymmetric device showed a high energy density due to its large potential window and high specific capacitance. To test and verify the practical application ability of the device, a blue light-emitting diode (LED) was successfully lit by two devices in series (shown in Figure 7d). In addition, they can also start a fan with the working potential of 3.3 V (shown in Figure 7f).

Figure 7.

Figure 7

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(a) CV curves of the GO/LTO-8 asymmetric supercapacitor device at various scan rates from 10 to 100 mV s–1; (b) GCD curves of the GO/LTO-8 asymmetric supercapacitor device at different current densities from 1 to 10 A g–1; (c) Ragone plot of the GO/LTO-8 asymmetric supercapacitor device; (d) specific capacitance after cycling; (e) blue LED was lit by two GO/LTO-8 asymmetric supercapacitor devices in series; and (f) fan with the working potential of 3.3 V was started by two GO/LTO-8 asymmetric supercapacitor devices in series (photograph courtesy of Munan Lu, copyright 2021).

For practical applications, the cycle stability is an important indicator. The cycle life of the fabricated device was verified by multiple charge/discharge cycles at 50 A g–1. The specific capacitance was measured for every 1000 cycles (shown in Figure 7d). As a result, the device reserved 85.0% capacitance after cycling 5000 times, exhibiting good cycling stability.

3. Conclusions

The GO/LTO composites were successfully prepared through a hydrothermal method and the LTO fibers dispersed homogeneously in and between GO sheets. The best ratio was determined by XRD, SEM, and electrochemical tests. The energy storage mechanism was investigated through FT-IR spectroscopy and XPS. The electrode of the GO/LTO-8 composite delivered a high specific capacitance of 900.6 F g–1 at the current density of 1 A g–1 with a large potential window of 1.8 V in the 1 M H2SO4 and 10 wt % sucrose aqueous electrolyte. The asymmetric two-electrode supercapacitor devices were assembled using GO/LTO-8 as active materials. The device showed a high specific capacitance of 208.8 F g–1 at the current density of 1 A g–1. Moreover, it also exhibited high energy density (94.0 Wh kg–1 at 750.1 W kg–1) and good cycle stability (85.0% capacity reserved after 5000 cycles). Since the simple preparation of GO/LTO composites exhibited excellent electrochemical properties, it provided a new idea for the energy industry.

4. Experimental Section

4.1. Preparation of GO Suspension

GO was synthesized from graphite flakes using an improved Hummer’s method.51 Briefly, 1 g of graphite flakes (≥325 mesh, Aladdin, China) were mixed with 120 mL of H2SO4 (98%, Aladdin, China) and 13 mL of H3PO5 (30%, Aladdin, China) at 10 °C in an ice bath, while 6 g of KMnO4 (AR, Aladdin, China) was added slowly in six portions. The mixture was kept stirring at 50 °C overnight. After cooling to room temperature, H2O2 (30 wt % solution, Aladdin, China) solution was added to the mixture and stirred for 3 h. The product was centrifuged and washed with HCl (10 wt % solution, Aladdin, China) and deionized water until the pH was neutral.

4.2. Synthesis of LTO Fibers

The LTO fibers were synthesized through the electrospun method as previously reported.35 Generally, a precursor was synthesized by poly(vinylpyrrolidone) (AR, Aladdin, China), La(NO3)3·6H2O (AR, Aladdin, China), and titanium tetraisopropanolate (AR, Aladdin, China). Then, the precursor was electrospun to obtain the precursor fibers. The precursor fibers were sintered at 750 °C to get the LTO fibers.

4.3. Synthesis of GO/LTO Composites

The GO/LTO composites were prepared through a hydrothermal reaction. LTO fibers and GO suspension were mixed in different mass ratios (2, 5, 8, and 10%) in deionized water, and ultrasonicated for 1 h. Then, they were transferred to a poly(tetrafluoroethylene) autoclave and heated at 110 °C for 6 h. After cooling to room temperature, the products were vacuum filtered and dried at 80 °C to obtain the GO/LTO composites (marked as GO/LTO-2, GO/LTO-5, GO/LTO-8, and GO/LTO-10).

4.4. Assembly of Asymmetric Supercapacitor

The GO/LTO electrode was attached to the stainless steel film current collector by the conductive adhesive. Then, two electrodes were separated by the semipermeable membrane and sealed in the laminating film. The 1 M H2SO4 and 10 wt % sucrose aqueous electrolyte was injected into the sealed device to assemble the asymmetric supercapacitor device (shown in Figure S3).

4.5. Characterization

The phase structure of the samples was identified by powder X-ray diffraction (XRD, Rigaku-D/max, Cu Kα). The elemental composition and chemical state of the composition were analyzed using an X-ray photoelectron spectrometer (XPS, ThermoFisher ESCALAB XI+, Al Kα). The structure of the sample surface was probed by Fourier transform infrared spectroscopy (FT-IR, VERTEX 70). The morphology of the composite was observed through scanning electron microscopy (SEM, JEOL JSM-7900F) with an energy dispersive spectrometer (EDS, Bruker XFlash 6|100).

4.6. Electrochemical Measurements

The GO/LTO composites were mixed with polyvinylidene fluoride (PVDF) as the binder and conductive carbon black as the conductive agent (mass ratio 80:10:10) in n-methyl pyrrolidone (NMP) and a slurry was formed. The working electrode was prepared by pressing the slurry (∼2 mg) on the carbon fabric and dried at 80 °C. Electrochemical measurements of the electrode were conducted with a CHI760E (Shanghai Chenhua, China) workstation with a three-electrode system. A platinum wire and a saturated calomel electrode (SCE) were applied as the counter electrode and reference electrode, respectively. The specific capacitance Cs (F g–1) was calculated from galvanostatic charge–discharge (GCD) curves with the following equation

4.6. 1

where It (A) is the charge/discharge current, t (s) is the discharge time, m (g) is the mass of the materials on each electrode, and ΔV (V) is the potential window.

The energy density (E, Wh kg–1) and power density (P, W kg–1) were calculated according to the following equations

4.6. 2
4.6. 3

Acknowledgments

This work was financially supported by the Recruitment Program of Guangdong (No. 2016ZT06C322).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c03863.

  • GCD curves of GO, LTO, and GO/LTO composites in 1 M H2SO4 electrolyte (Figure S1); CV and GCD curves of the GO, LTO, and GO/LTO composites, and C/LTO-8 in 1 M H2SO4 electrolyte: (a) CV curves of GO; (b) GCD curves of GO; (c) CV curves of GO/LTO-2; (d) GCD curves of GO/LTO-2; (e) CV curves of GO/LTO-5; (f) GCD curves of GO/LTO-5; (g) CV curves of GO/LTO-8; (h) GCD curves of GO/LTO-8; (i) CV curves of GO/LTO-10; (j) GCD curves of GO/LTO-10; (k) CV curves of C/LTO-8; and (l) GCD curves of C/LTO-8 (Figure S2); assembly of the asymmetric supercapacitor device (Figure S3) (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao1c03863_si_001.pdf (373.8KB, pdf)

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