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3D Interconnected Binder-Free Mn-Ni-S Nanosheets for High Performance Asymmetric Supercapacitor Devices with Exceptional Cyclic Stability Nashaat Ahmed, Basant A. Ali, mohamed ramadan, and Nageh K. Allam ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00435 • Publication Date (Web): 12 Apr 2019 Downloaded from http://pubs.acs.org on April 12, 2019

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ACS Applied Energy Materials

3D Interconnected Binder-Free Mn-Ni-S Nanosheets for High Performance Asymmetric Supercapacitor Devices with Exceptional Cyclic Stability

Nashaat Ahmed, Basant A. Ali , Mohamed Ramadan , and Nageh K. Allam*

Energy Materials Laboratory (EML), School of Sciences and Engineering, the American University in Cairo, New Cairo, 11835, Egypt.

ABSTRACT A facile one-step method was demonstrated for the electrodeposition of manganese-nickel sulﬁde (Ni-Mn-S) 3-D interconnected sheets on nickel foam substrates. The as-synthesized materials were characterized using field‐emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), and X‐ray photoelectron spectroscopy (XPS) techniques. Upon their use as supercapacitor electrodes, the electrodeposited Mn-Ni-S showed exceptionally high speciﬁc capacitance (2849 F/g and 1986 F/g at 1 A/g and 5 A/g, respectively) and an excellent rate capability. Using Fe 3 O 4 -GR as the negative electrode and the Mn-Ni-S 3D interconnected sheets as the positive electrode to assemble asymmetric supercapacitor device revealed high power density (800 W kg-1) and energy density (40.44 Wh kg1

) with 90 % capacitance retention and a Columbic efficiency of 100% after 11,000 cycles,

indicating the high potential of the fabricated materials for practical energy storage devices.

Keywords: Mn-Ni-S sheets, electrochemical deposition, XPS, binder-free, Impedance, asymmetric supercapacitors. *

Corresponding Author: [email protected]

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INTRODUCTION The rapid increase in population and the modern technological world necessitate an increasing trend in the consumption of resources, leading to imminent energy crises. Therefore, identifying new, clean, and efficient energy sources and developing new energy storage technologies and devices have become a research topic of great interest. Compared with traditional capacitors, supercapacitors have higher specific capacitance and higher energy density. Compared with batteries, supercapacitors have higher power density, longer life, fast charge-discharge rate, low cost, easy manufacture processes, and being environmentally friendly1,2. Thus, supercapacitors are promising to be used in many applications such as petroleum-electric hybrid vehicles, and smart wearable products

3–5

. However, the low energy density of the reported

supercapacitors is the bottleneck hindering their actual use in real applications. To this end, researchers are very active trying to identify suitable electrode materials6–9 and electrolytes10,11 that can overcome such limitation. To this end, transition metal sulfides, such as CoS, MnS and NiS, have been widely investigated with very promising results reported

12–18

. More recently,

mixtures of those sulfides, such as Ni-Mn-S, have also been investigated. Cheng et. al 19 showed the supercapacitor made of Ni-Mn-S to result in 1636 F/g at 2 A/g with an excellent stability of 95% after 4000 cycle. Also, Wan et. al20 reported a capacitance of 1016 F/g at 0.5 A/g. Based on those promising results, many studies were devoted to investigate the effect of the Ni:Mn ratio on the structure and performance of the mixed sulfide materials

19,21

. However, the reported

fabrication methods are tedious multistep processes and non-environmental friendly. Moreover, the reason behind the higher capacitance of mixed sulfide than their individual counterparts is not well-identified and explained. One more important point is to identify a means to achieve high power density, the main advantage of supercapacitors, along with high capacitance. As the power


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density is directly affected by the operating potential window, identifying counter electrodes that maintain both capacitance and high power density should be one of the main targets to enable the design of high performance supercapacitor devices 22. In this contribution, we report on a facile and green one-step method to fabricate disulfide materials to overcome the above mentioned limitations. Specifically, hierarchically 3D interconnected Mn-Ni-S sheets with controlled composition were grown via electrochemical codeposition on nickel foam. Upon their use as positive electrodes in a three-electrode cell, they showed exceptionally high capacitance of 2849 Fg-1 at a current density of 1A g-1. On the other hand, the asymmetric supercapacitor device, made of the as-synthesized Mn-Ni-S 3D interconnected sheets positive electrode and Fe 3 O 4 -GR negative electrode, shows very high energy density (40.44 Wh kg—1) and power density (0.8 kW kg—1) at 1 Ag-1.

EXPERIMENTAL SECTION Materials. The used chemicals in this study were analytical grade and used without any further pre-treatments. Nickel nitrate hexahydrate (Ni(NO 3 ) 2 .6H 2 O 98%, Alfa Aesar, UK), Manganese chloride tetrahydrate (MnCl 2 .4H 2 O, 98%, Sigma Aldrich, USA), potassium chloride (KCl, Alfa Aesar, UK), Thiourea (H 2 NCSNH 2 , 99%, Alfa Aesar, UK), hydrazine hydrate (99%, Sigma Aldrich, USA), Graphite powder (Sigma Aldrich), anhydrous Iron (III/II) chloride (99.9+ %), and potassium hydroxide (KOH, 85%, Alfa Aesar, UK) were used for the synthesis and device assembly of the Mn-Ni-S nanoflakes. Deionized water was used in all experiments.



Electrodeposition of Mn-Ni-S 3D interconnected sheets

The Mn-Ni-S 3D interconnected sheets were co-deposited electrochemically onto the flexible nickel foam using a biologic SP 300 potentiostat/galvanostat. The electrodeposition solution consists of 0.01M KCl, 0.1 M Thiourea (CS(NH 2 ) 2 , 0.01M Ni(NO 3 ) 2 .6H 2 O, and 0.01M MnCl 2 .4H 2 O. The nickel foam substrate was initially cleaned in concentrated HCl solution in ultrasonic bath for 15 min to remove the native NiO layer, followed by rinsing with DI water and ethanol. The electrodeposition was done in a three-electrode cell with the cleaned Ni foam as the working electrode, platinum sheet as the counter electrode, and saturated calomel electrode as the reference electrode using cyclic voltammetry in the potential range of -1.2–0.2 V at a scan rate of 5 mV s—1 for 5 cycles. The prepared electrodes were washed several times using DI water followed by drying at 60°C for 12 h. The mass of the deposited film on the Ni foam was determined as the difference between the mass of the Ni foam before and after electrodeposition using a microbalance. The typical mass loading of the positive Mn-Ni-S electrode was about 0.6 mg.cm2

. For comparison, the electrodeposition of Mn-S and Ni-S nanosheets was performed by the same

method. Synthesis of magnetite– graphene (Fe 3 O 4 -GR) composites

Graphene oxide was synthesized via the improved Hummers’ method as previously reported23,24. The Fe 3 O 4 -GR was prepared via hydrothermal method. A specific amount of Graphene oxide was first dispersed in 50ml DI water, then 5 mg FeCl 3 .6H 2 O and 2 mg FeCl 2 .4H 2 O were added to the GO solution. The mixed solution was stirred overnight at 70 oC. Then, 30% ammonia solution was added to the solution to form a solution of pH =11, then the mixture was transferred to a Teflon sealed autoclave and set at 150 oC for 2 hours, followed by filtration, washing, and drying. The Fe 3 O 4 -GR slurry was prepared by mixing 80 wt.% Fe 3 O 4 -GR, 10 wt. % carbon, and 10 wt. % 4 ACS Paragon Plus Environment

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PVDF in DMF as a solvent, which was then drop-casted onto NF, followed by drying at 60 °C for 12 h.

Material Characterization.

The morphology of the prepared samples was characterized utilizing a Zeiss SEM Ultra 60 field emission scanning electron microscope (FESEM), and the composition was examined by EnergyDispersive X-ray Analysis (EDX) associated with FESEM. The crystallinity of the prepared materials was investigated by X-ray diffraction (XRD), in the scanning range from 5° to 80°, with a step size 0.03°, The composition of the fabricated films was characterized using X-ray photoelectron spectrometer (XPS, Kratos-England) with a monochromatic Al-Kα X-ray source (hυ = 1486.6 eV). Electrochemical Measurements.

The supercapacitive properties of the fabricated electrodes were tested in 1.0 M KOH solution in a three-electrode cell with a Pt wire counter electrode and a reference electrode (saturated calomel electrode (SCE)). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) tests were carried out using Biologic SP 300. The CV measurements were performed in the potential window of 0 - 0.45 V at different scan rates from 5 to 50 mV s-1. The GCD measurements were investigated in the potential window of 0 - 0.4 V at different current densities (1 - 20 A g-1). The EIS measurements were performed at the open circuit potential over the frequency range of 0.01 Hz to 100 kHz with a sinusoidal perturbation of 10 mV amplitude. Then, the specific capacitance (Cs, F g-1) was calculated from the GCD according to the following equation:25 𝐶𝐶𝐶𝐶 =

I∆t m∆V

(1) 5

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𝐶𝐶 =

I∆t m

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(2)

where I is the discharge current (A), Δt is the discharging time (s), m is the mass of active material (g) within the electrode, and ΔV is the discharge voltage range (V). Fabrication of Mn-Ni-S // Fe 3 O 4 -GR asymmetric supercapacitor.

The assembly of the Mn-Ni-S // Fe 3 O 4 -GR asymmetric supercapacitors was performed by using Fe 3 O 4 -GR and Mn-Ni-S as the negative and positive electrodes, respectively with a filter paper as the separator and 1.0 M KOH solution as the electrolyte. The masses were balanced for the two electrodes (positive and negative) in a voltage range of ΔV according to Eqs. 3 and 4 :25 𝑄𝑄+= 𝑄𝑄 − 𝑚𝑚+ m−

=

(3)

𝐶𝐶− ∗Δ𝑉𝑉 𝐶𝐶+ ∗Δ𝑉𝑉

(4)

where m is the mass and C s is the specific capacitance, with a typical mass loading of the asymmetric supercapacitor of 5.2 mg/cm2.

RESULTS AND DISCUSSION

The electrodeposition of Mn-Ni-S was performed using cyclic voltammetry by sweeping the potential from -1.2 to 0.2 V to allow Mn2+, Ni2+, and S2- ions in solution to be deposited onto the Ni foam substrate, resulting in Mn-Ni-S 3D interconnected sheet-like structure. Note that cyclic voltammetry allows the deposition of uniform film over the electrode surface, where the thickness can be controlled by limiting the number of sweeping cycles26. The color of the Ni foam turned 6 ACS Paragon Plus Environment

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yellow once the film is deposited, which is a characteristic of Mn-Ni-S.

A plethora of

characterization techniques have been used to confirm the growth of Mn-Ni-S on Ni foam. Figure 1a shows the glancing angle x-ray diffraction (GAXRD) pattern of the fabricated electrode. The XRD spectrum exhibits different diffraction peaks at 2θ of 35.90°, 41.42°, 51.71°, and 76.09°, corresponding to the (101), (002), (110), and (202) plans with interplaying distances (d) of 2.5, 2.184, 1.761, and 1.25 Å, respectively, characteristic of hexagonal NiS 2 (ICDD Card no. 01-0799982). The peaks at 2θ of 36.23°, 51.9°, 64.8°, and 76.54°, with d-spacing of 2.48, 1.75, 1.436, and 1.242 Å, respectively can be ascribed to the (200), (220), (222), and (400) planes of cubic αMnS (ICDD Card no. 01-076-6011). Note also the characteristic peaks for γ- NiS at 41.6°, 74.86°, and 44.18° with d-spacing of 2.17, 1.27, and 2.05 Å, respectively (ICDD Card no. 00-003-1170). Moreover, there are characteristic peaks related to the nickel foam substrate at 44.52°, 51.96°, and 76.6°, corresponding to the (111), (200), and (220) planes, respectively (ICDD card no. 04-0048734). Therefore, the composition and surface electronic states of the as-prepared Mn-Ni-S electrodes were investigated by X-ray photoelectron spectroscopy (XPS). Figure 1b shows the Mn 2p photoelectron spectrum, where doublet peaks of Mn 2p1/2 and Mn 2p3/2 were detected at 654.3 eV and 642.8 eV, respectively. Using Gaussian fitting, the overlapped Mn 2p 3/2 peak was deconvoluted into three peaks at ~642 eV, ~643.9 eV, and ~647.5 eV, which are characteristic of Mn2+, Mn3+, and Mn4+ species27–29, respectively. Similarly, the coexistence of Ni2+and Ni3+species was evident from the deconvolution of the Ni 2p peaks (Figure 1c), with the Ni2+ peak being more intense than Ni3+. Furthermore, intense satellite peaks (marked as Sat.) were observed, indicating that Ni2+ is the main oxidation state present30,31. For the XPS spectrum of Sulfur (Figure 1d), the S 2p spectrum revealed two peaks, one satellite peak (~168.1 eV), and a main peak (~163 eV). The former peak is assigned to the surface-adsorbed oxidized sulfur species such as sulfates and



hydrogen sulfates. The other overlapped main peak was deconvoluted into two peaks; S 2p 3/2 (~161.9 eV), which is ascribed to metal-sulfur bonds (Mn–S and Ni–S bonds), and S 2p 1/2 (~163.4 eV), which is assigned to sulfur ions with low coordination numbers32–34.

Figure 1. (a) XRD pattern for Mn-Ni-S, (b-d) HR-XPS of Mn 2p, Ni 2p, and S2p respectively.

Figure 2a, b shows FESEM images of the film grown on the Ni foam substrate. Note the formation of a homogenous 3D interconnected sheets-like structure. The thickness of the grown Mn-Ni-S film is estimated to be only approximately 300 nm as shown in Figure 2-c, and the sheet thickness ranged from12 to 18 nm as shown in Figure 2d. Besides, the EDX analysis (Figure 2e) shows the coexistence of Ni, Mn and S with no extra peaks of foreign elements, indicating the


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formation of the Mn-Ni-S with high purity. The EDX mapping (Figure 2f-h) clearly shows that Mn, Ni, and S are evenly distributed.

Figure 2. FESEM images of the electrodeposited Mn-Ni-S nanosheets, (a, b) top view images at low and high magnification, respectively, (c, d) the corresponding side view images, (e) EDS spectrum of the fabricated Mn-Ni-S, and the EDS mapping of (f) Ni, (g) Mn, and (h) S.



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Electrochemical performance of the fabricated materials

The electrochemical performance of the deposited Mn-Ni-S was compared to that of NiS, MnS and Mn-Ni-S that have been deposited under the same conditions, Figure 3. The electrochemical test was performed in a 3-electrode cell in 1.0 M KOH as the electrolyte with the sulfide material acting as the positive electrode. All tested electrodes showed clear redox peaks in the cyclic voltammograms, Figure 3a, which originate from the reaction between KOH and the sulfide material. The reactions can be described by Eqs. 5-7 below13: NiS + OH- → NiS-OH + e-

(5)

NiS 2 + OH- → NiS 2 -OH + e-

(6)

MnS + OH- → MnS-OH + e-

(7)

At a scan rate of 5 mV/s, the CV curve showed two peaks that are characteristic of secondary sulfides35. While the higher current peak can be ascribed to the participation of NiS, the lower current peak can be related to the participation of the MnS. Upon increasing the scan rate to 50 mV/s (Figure 3b), the behavior of the Mn-Ni-S maintained its behavior and the two peaks were better matching the peaks of NiS and MnS, respectively. A comparison between the specific capacitance values of the tested sulfide materials at different scan rates is presented in Figure 3c. At all scan rates, the specific capacitance of Mn-Ni-S was higher than that of both NiS and MnS. For example, at 5 mV/s the specific capacitance of Mn-Ni-S was as high as 3205 F g-1, which is higher than that of both NiS (1829.27 F g-1) and MnS (1363 F g-1). The exceptionally high capacitance of the mixed sulfide electrode can be related to the synergism between the two high capacitance metal sulfides. Note that the obtained specific capacitance is higher than those reported in literature for the same composition but prepared but other methods, see Table 1. Although the specific capacitance of Mn-Ni-S decreases at higher scan rates, the material maintained its higher 10 ACS Paragon Plus Environment

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overall capacitance with a specific capacitance of 1188 F g-1. As the charge and discharge characteristics of the electrodes is the main factor to identify the good charge storage and delivery, GCD measurements were performed for the fabricated sulfide electrodes at different current densities. Figure 3d illustrates the comparative GCD curves of the sulfide electrodes at 1.0 Ag-1. The GCD curves show symmetric charge and discharge behavior that resembles the typical battery-like supercapacitor behavior, which is maintained at a higher current density of 20 Ag-1 (Figure 3e). The specific capacitance calculated from the GCD showed also a great enhancement upon the combination of Mn and Ni sulfides. The comparison between the specific capacitance of the fabricated sulfide electrodes is presented in Figure 3d. The specific capacitance of Mn-Ni-S at a current density of 1 A g-1 (2841.25 F g-1) was much higher than that of NiS, MnS, and previously reported values in literature, Table 1. At high current density of 20 A g-1, the Mn-Ni-S electrode maintained its excellent specific capacitance of 1334 F g-1.

Figure 3. Electrochemical performance of sulfide electrodes in a 3-electrode cell, (a) CVs of sulfide materials at a scan rate of 5 mV/s, (b) CVs of sulfide materials at 50 mV/s, (c) variation of the specific capacitance with the scan rate, (d) GCDs of sulfide materials at 1 A g-1, (e) GCDs of sulfide materials at 20 A g-1, and (f) variation of the specific capacitance with current density. 11 ACS Paragon Plus Environment


Figure 4a shows the CV curves of the Mn-Ni-S at different scan rates. Upon increasing the scan rate, the cathodic peaks were shifted to lower potentials while the anodic peaks were shifted to higher potentials. At high scan rate, the difference in the diffusion rate of the electrolyte (OH−), which is not fast enough to accomplish the electrochemical reactions at the active electrode material, is the mean reason behind the shift in the redox peaks. The GCD curves of the Mn-Ni-S in the potential range from 0 to 0.45 V at different current densities exhibited obvious voltage plateaus, indicating battery-like supercapacitive behavior. The calculated values of specific capacitance from each discharging curve were 2841.25, 2328, 1860, 1608.5, 1334, 1132.5,951, and 856.25 F g-1 at current densities of 1, 2, 5, 10, 20, 30, 40, and 20 A g-1, respectively. The MnNi-S maintained its behavior and stability over high current densities. To further investigate the charge storage behavior of the Mn-Ni-S, Tafel’s plot (i= avb) is illustrated in Figure 4c, where the slope (b) indicates the predominant charge storage mechanism. While a slope of b=0.5 indicates diffusion-controlled process, a slope of b=1 indicates a surface process36,37. The obtained b value for the Mn-Ni-S electrode was 0.55 and 0.62 for the cathodic and anodic peaks, respectively, which are similar to those obtained for NiS electrode. However, those values were 0.59 and 0.63 for the cathodic and anodic peaks of the MnS electrode. This indicates a predominant diffusion-controlled process of the charge storage mechanism in all sulfide electrodes, giving an insight on the origin of the observed redox peaks of the Mn-Ni-S, which can be ascribed to NiS.


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Figure 4. Electrochemical performance of Mn-Ni-S electrode in the 3-electrode system. (a) CVs of MnNi-S at different scan rates, (b) GCDs of Mn-Ni-S at different current densities, and (c) Tafel’s plot of Mn-Ni-S electrode.



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Table 1 Comparison of previous reports on Mn-Ni-S as an electrode material for supercapacitors with our fabricated material. Material

Synthesis

Substrate

Electrolyte

Capacitance

Condition

Retention

No. of

Pot.

Cycles

Window,

Ref.

(V) Ni-Mn-S Ni‒Mn-S

Electrodeposition

Hydrothermal

Ni foam

Ni foam

1 M KOH

3205 F/g

5 mV/s

Device

Device

2841.25 F/g

1A/g

(90%)

(11,000)

1068 F/g,

1 A/g

90%

1500

0 - 0.55

21

2 mA/cm2

96.5%

1000

0 - 0.6

38

1430 F/g

0.5 A/g

---

100

-0.1 - 0.5

20

268 F/g

10 A/g

6 M KOH

0 - 0.45

This work

2:1 Ni:Mn Ni 3 S 2 /MnS

Etching and

Ni foam

3 M KOH

6.7 mAh/cm2

pre-oxidation Ni-MnS

Hydrothermal

Ni foam

6 M KOH

Ni–MnS

Self-template

Ni foam

3 M KOH

1636.8 F/g

2 A/g

95.1%

4000

0 - 0.4

39

MnS/Ni x S y

Hydrothermal

Ni foam

3 M KOH

1073.81 F/g

1 A/g

82.14%

2500

0 - 0.45

13

To further explore the Mn-Ni-S electrode for potential practical applications, asymmetric supercapacitor devices were assembled by combining the Mn-Ni-S as the positive electrode, Fe 3 O 4 -GR as the negative electrode, and a filter paper as the separator, Figure 5, and tested in 1.0 M KOH solution.

Figure 5. Schematic illustration of the assembled asymmetric supercapacitor. 14 ACS Paragon Plus Environment

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The electrochemical performance of the asymmetric supercapacitor cell was investigated. Figure 6a shows the CV scans of the asymmetric Mn-Ni-S//Fe 3 O 4 -GR supercapacitor over the potential range of 0 to 1.6 V at different scan rates from 5 to 50 mV s-1 in an aqueous 1.0 M KOH solution. Note the Faradic behavior of the Mn-Ni-S//Fe 3 O 4 -GR asymmetric supercapacitor as evidenced by the feasible redox peaks in the CV graphs 25. This Faradic-type behavior can also be observed in the GCD curves obtained at different current densities (Figure S1 and Figure 6b). The small IR drop in the discharge curves even at high current densities indicate a low device resistance. Additionally, the GCD profiles are perfectly symmetric, which indicate a reversible electrochemical process and high Columbic efficiency22. Figure 6c illustrates the variation of the rate capability of our fabricated device over a broad range of current densities ranged from 1 to 20 A g−1. Note that the specific capacitance reaches a maximum of 113.75 F g−1 at 1 A g−1 and sustains a capacitance of 47.5 F g−1 at a high current density of 20 A g−1. This exceptional rate capability performance can be ascribed to the 3 D interconnected structure of the fabricated Mn-Ni-S electrode, which is easily accessible by the electrolyte as well as the excellent characteristics of the negative electrode. Figure 6d shows the Nyquist plot of the Mn-Ni-S//Fe 3 O 4 -GR device in the frequency range of 0.01 Hz–100 kHz. Note the low charge transfer resistance in the high frequency regime, indicating a facile Faradic behavior of the device. Moreover, the assembled asymmetric supercapacitor device exhibits excellent characteristics as indicated by the very low internal resistance (small intercept of the Nyquist plot) and the linear part at low frequencies

22,35

. Upon

evaluating the stability of the fabricated device, only 10 % capacitance decay, at a current density of 10 Ag-1, was observed with a very high columbic efficiency reaching 100% after 11,000 cycles, indicating the remarkable stability and reversibility of the device as shown in Figure 6e.



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Consequently, the energy density (E) and power density (P) were calculated using Eqs. 8 and 9, taking into account the total weight of the positive and negative electrodes in the devices40,41. 𝐸𝐸 = 𝑃𝑃 =

𝐶𝐶𝑉𝑉 2

(8)

2

𝐸𝐸

𝑡𝑡𝑑𝑑

=

𝐶𝐶𝑉𝑉 2

(9)

2𝑡𝑡𝑑𝑑

where C is the capacitance, t d is the discharge time obtained from the discharge curve, and V is the maximum voltage applied during the charge/discharge measurement. Figure 6f shows Ragone plot (E vs. P) for the Mn-Ni-S//Fe 3 O 4 -GR asymmetric supercapacitor. The obtained energy and power densities of our devices (40.44 Wh kg-1, 0.8 kW kg-1 and 15.831 kW kg-1, 16.71 Wh kg-1) are higher than most of the recently reported values for asymmetric aqueous supercapacitor devices: (MnO 2 //graphene 42 showing a power density of 1 kW kg-1 with an energy density of 23.2 Wh kg-1, MWCNT-Ni 3 S 2 //activated carbon 43 resulting in a power density of 798 W kg-1 with an energy density of 19.8 Wh kg-1, NiCoS //activated carbon 44 with a power density of 447 W kg-1 and an energy density of 25 Wh kg-1, NiCo 2 O 4 /graphene//AC 45 giving a power density of 5600 W kg -1 with an energy density of 7.6 Wh kg-1, MnO 2 -graphene //graphene 46 with a power density of 100 Wkg-1 and an energy density of 30.4 Wh kg-1, CoO nanowire arrays – polypropylene//AC 47

showing a power density of 5500 W kg-1 with an energy density of 11.8 Wh kg-1, and Ni(OH) 2

free standing nanoporous film//exfoliated graphite oxide48 with an energy density of 6.9Wh kg-1 and a power density of 44000 Wkg-1. Finally, for practical applications, three series‐connected ASC devices successfully glow up a 3 V LEDs, Figure 6g, for 1500 s, indicating the great potential of the assembled Mn-NiS//Fe 3 O 4 -GR SC for energy storage applications.


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Figure 6. Electrochemical performance of the Mn-Ni-S//Fe 3 O 4 -RGO asymmetric supercapacitor: (a) CV curves at different scan rates ranging from 5 to 50 mVs-1, (b) GCD curves at various current densities ranging from 7 to 20 A g−1, (c) calculated capacitance at different current densities, (d) Nyquist plots of the device, (e) capacity retention and columbic efficiency for 11,000 cycle at a current density of 10 A g-1, (f) Ragone plot comparing the performance of our device with those reported in literature, and (g) glowing LED for 1500 s. 17 ACS Paragon Plus Environment


Conclusion In summary, 3D interconnected Mn-Ni-S nanosheets (12-18 nm thick) were synthesized by a facile one-step electrodeposition method as confirmed via FESEM imaging, EDS, and XPS analysis. The XPS analysis showed the existence of Mn2+, Mn3+, and Mn4+ as well as Ni2+and Ni3+. Due to the unique structure and composition of the interconnected nanosheets, Mn-Ni-S exhibited a very high specific capacitance (2849 F g-1 at 1 A g-1) with a capacitance retention of 90% after 11,000 cycles. The assembled asymmetric device enjoys 100% Columbic efficiency with high energy density (40.44 Wh/kg) and power density (800 W/kg). The device achieves 90% capacitance retention. The high conductivity and porosity are believed to be responsible for the observed exceptional electrochemical performance of the fabricated Mn-Ni-S nanosheets, allowing fast electrons/ions transport. The obtained results highlight the promising applications of Mn-Ni-S nanosheets structure as a potential candidate for effective energy storage devices.

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ASSOCIATED CONTENT

Supporting Information

The Supporting Information is available free of charge on the ACS Publications website at DOI: GCD curves obtained at different current densities ranged from 1-7 Ag-1.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Nashaat Ahmed: 0000-0002-4251-2309 Basant A. Ali: 0000-0002-6961-257X Mohamed Ramadan: 0000-0002-6155-3413 Nageh K. Allam: 0000-0001-9458-3507

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Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENT

The financial support by the Egyptian Academy of Scientific Research and Technology (ASRT) under JESOR grant is highly appreciated.

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3D Interconnected Binder-Free Mn-Ni-S Nanosheets for High- Performance Asymmetric Supercapacitors with Exceptional Cyclic Stability 219x152mm (72 x 65 DPI)


3D Interconnected Binder-Free Mn-Ni-S ... - ACS Publications

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