**2. Experimental details**

In this study, supercapacitor working electrodes were fabricated using 304L stainless steel as current collector (0.5 mm thick, 9 cm2 area) coated with sputter CrN thin film. Prior to deposition, the steel substrates were polished with SiC abrasive paper and ultrasonically washed with alcohol and acetone, respectively. The thin film deposition was carried out for 60 min by applying 50 W power and 5 mTorr (Ar:N2::1:1) working pressure using Cr target (99.99% pure, Testbourne Ltd., UK), keeping the current collector at 5 cm and 300°C.

The sputtered CrN thin films were characterized via X-ray diffraction (Bruker AXS, D8 advance), FE-SEM (Carl Zeiss, Ultra plus), energy dispersive X-ray analysis (EDAX, Oxford Instruments), Raman spectroscopy (Renishaw, United Kingdom), and X-ray photoelectron spectroscopy (XPS, PerkinElmer model 1257). The supercapacitive behavior of CrN working electrodes was examined via electrochemical workstation (CHI-660D) in a three-electrode cell in 1 M Na2SO4 solution.

The specific capacitance (F/g) of working electrode was calculated from the CV curves using Eq. (1), respectively:

$$\mathbf{C\_s} = \frac{\mathbf{Q}}{\mathbf{m} \, \mathbf{x} \, \Delta \mathbf{V}} = \frac{\int\_{-\mathbf{V}}^{\mathbf{V}} \mathbf{I}(\mathbf{V}) \mathbf{d} \mathbf{V}}{\mathbf{m} \, \mathbf{x} \, \Delta \mathbf{V} \, \mathbf{x} \, \mathbf{v}} \tag{1}$$

Where specific capacitance Cs is in F/g, Q is charge in coulomb, m is mass of the active material in gram, *v* is the scan rate in V/s, and ∆V is the potential window between the positive (V+) and negative (V−) electrodes in volt [3]. The loading mass of active material was around ~12 mg.

### **3. Results and discussion**

As depicted in **Figure 1**, the XRD spectrum of sputtered cubic CrN thin films shows three characteristic peaks at 37.45°, 43.35°, and 63.37 corresponding to (111), (200), and (220) planes (JCPDS file no. 110065) [15]. The working electrode also shows three characteristic peaks at 44.54°, 50.56°, and 73.96° corresponding to (111), (200), and (220) planes of cubic phase of 304 L steel substrate (JCPDS file no. 10752128) [16].

As shown in **Figure 2**, the CrN thin film depicts two Raman active modes centered at 238 cm<sup>−</sup><sup>1</sup> corresponding to vibrations of metal atoms, and 619 cm<sup>−</sup><sup>1</sup> corresponding to vibrations of lighter nonmetal ions [17].

As depicted in **Figure 3**, XPS measurements were carried out to study the chemical structure of CrN film. The XPS spectra of N1 s depict two binding energies peaks at 396.96 and 398.56 eV, corresponding to the CrN and adsorbed nitrogen, respectively (**Figure 3a**). The XPS spectra of Cr2p3/2 depict a peak at 575.76 eV corresponding to CrN (**Figure 3b**), well corroborated with the XRD and Raman results [18].

As depicted in **Figure 4a** and **b**, the FE-SEM images represent columnar porous morphology of CrN working electrode. The EDS spectra represents the stoichiometric chemical composition (1:1) of CrN working electrode.

To compare the CrN film and current collector, the CV curves were measured at a high scan rate of 200 mV/s. The CV curve depicted that CrN film is key contributor in supercapacitive performance as working electrode swept a more area than that of the current collector (**Figure 5a**). The CV plots of working electrode were tested between 0 and 1.2 V range at scan rates 5–200 mV/s in 1 M Na2SO4

**109**

**Figure 1.**

**Figure 2.**

*2018)*[23].

*Copyright 2018)*[23].

active sites of CrN films.

*CrN Sputtered Thin Films for Supercapacitor Applications*

solution (**Figure 5b**). The CV curves of working electrode showed the symmetric and reversible plots with good capacitive behavior [19]. The plot between specific capacitance (Cs) versus scan rates is represented in **Figure 5c**, showing 41.66, 31.25, 16.7, 12.5, and 11.2 F/g at the scan rates of 5, 20, 50, 100, and 200 mV/s, respectively,

*Raman spectrum of CrN thin film. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright* 

*XRD pattern of CrN working electrode. (Adapted from Mohd. Arif et al., with permission from Elsevier.* 

**Table 1** shows the specific capacitance values of present case along with previ-

demonstrated excellent capacitance retention of 87% after 2000 cycles at a scan rate of 200 mV/s [21]. The reduction in capacitive retention is due to the dissolution of

ously reported literature. As shown in **Figure 5d**, the CrN working electrode

well corroborated with the available literature [18, 20].

*DOI: http://dx.doi.org/10.5772/intechopen.81469*

*CrN Sputtered Thin Films for Supercapacitor Applications DOI: http://dx.doi.org/10.5772/intechopen.81469*

#### **Figure 1.**

*Science, Technology and Advanced Application of Supercapacitors*

stainless steel as current collector (0.5 mm thick, 9 cm2

UK), keeping the current collector at 5 cm and 300°C.

In this study, supercapacitor working electrodes were fabricated using 304L

ter CrN thin film. Prior to deposition, the steel substrates were polished with SiC abrasive paper and ultrasonically washed with alcohol and acetone, respectively. The thin film deposition was carried out for 60 min by applying 50 W power and 5 mTorr (Ar:N2::1:1) working pressure using Cr target (99.99% pure, Testbourne Ltd.,

The sputtered CrN thin films were characterized via X-ray diffraction (Bruker

AXS, D8 advance), FE-SEM (Carl Zeiss, Ultra plus), energy dispersive X-ray analysis (EDAX, Oxford Instruments), Raman spectroscopy (Renishaw, United Kingdom), and X-ray photoelectron spectroscopy (XPS, PerkinElmer model 1257). The supercapacitive behavior of CrN working electrodes was examined via electrochemical workstation (CHI-660D) in a three-electrode cell in 1 M Na2SO4 solution. The specific capacitance (F/g) of working electrode was calculated from the CV

<sup>m</sup> <sup>x</sup> ΔV <sup>=</sup>

Where specific capacitance Cs is in F/g, Q is charge in coulomb, m is mass of the active material in gram, *v* is the scan rate in V/s, and ∆V is the potential window between the positive (V+) and negative (V−) electrodes in volt [3]. The loading

As depicted in **Figure 1**, the XRD spectrum of sputtered cubic CrN thin films shows three characteristic peaks at 37.45°, 43.35°, and 63.37 corresponding to (111), (200), and (220) planes (JCPDS file no. 110065) [15]. The working electrode also shows three characteristic peaks at 44.54°, 50.56°, and 73.96° corresponding to (111), (200), and (220) planes of cubic phase of 304 L steel substrate (JCPDS file

As shown in **Figure 2**, the CrN thin film depicts two Raman active modes

As depicted in **Figure 3**, XPS measurements were carried out to study the chemical structure of CrN film. The XPS spectra of N1 s depict two binding energies peaks at 396.96 and 398.56 eV, corresponding to the CrN and adsorbed nitrogen, respectively (**Figure 3a**). The XPS spectra of Cr2p3/2 depict a peak at 575.76 eV corresponding to CrN (**Figure 3b**), well corroborated with the XRD and Raman results [18]. As depicted in **Figure 4a** and **b**, the FE-SEM images represent columnar porous morphology of CrN working electrode. The EDS spectra represents the stoichio-

To compare the CrN film and current collector, the CV curves were measured at a high scan rate of 200 mV/s. The CV curve depicted that CrN film is key contributor in supercapacitive performance as working electrode swept a more area than that of the current collector (**Figure 5a**). The CV plots of working electrode were tested between 0 and 1.2 V range at scan rates 5–200 mV/s in 1 M Na2SO4

corresponding to vibrations of lighter nonmetal ions [17].

metric chemical composition (1:1) of CrN working electrode.

corresponding to vibrations of metal atoms, and 619 cm<sup>−</sup><sup>1</sup>

∫

−V <sup>V</sup> I(V)dV \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

area) coated with sput-

<sup>m</sup> <sup>x</sup> ΔV <sup>x</sup> <sup>v</sup> (1)

**2. Experimental details**

curves using Eq. (1), respectively:

**3. Results and discussion**

no. 10752128) [16].

centered at 238 cm<sup>−</sup><sup>1</sup>

Cs <sup>=</sup> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ <sup>Q</sup>

mass of active material was around ~12 mg.

**108**

*XRD pattern of CrN working electrode. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

#### **Figure 2.**

*Raman spectrum of CrN thin film. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

solution (**Figure 5b**). The CV curves of working electrode showed the symmetric and reversible plots with good capacitive behavior [19]. The plot between specific capacitance (Cs) versus scan rates is represented in **Figure 5c**, showing 41.66, 31.25, 16.7, 12.5, and 11.2 F/g at the scan rates of 5, 20, 50, 100, and 200 mV/s, respectively, well corroborated with the available literature [18, 20].

**Table 1** shows the specific capacitance values of present case along with previously reported literature. As shown in **Figure 5d**, the CrN working electrode demonstrated excellent capacitance retention of 87% after 2000 cycles at a scan rate of 200 mV/s [21]. The reduction in capacitive retention is due to the dissolution of active sites of CrN films.

#### **Figure 3.**

*(a) XPS spectra of N1 s, and (b) XPS spectra of Cr2p3/2. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

#### **Figure 4.**

*(a and b) FE-SEM images of CrN thin film at different scales, 200 and 100 nm scales, and (c) EDS spectrum of CrN thin film. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

The EIS spectroscopy of CrN working electrode was measured between the frequency range of 0.01 and 100 kHz. As depicted in **Figure 5e**, the Nyquist plot of CrN working electrode showed a straight line in low frequency range, which represents the diffusion of ions at the electrode-electrolyte interface [22]. The Nyquist plot of CrN working electrodes showed a semicircle in high frequency range, which represents the electronic resistance and contact resistance between active material and current collector (inset of **Figure 5e**). The equivalent circuit model of working electrode is shown in **Figure 5f**. From the EIS circuit model, the electrolyte resistance (Rs) was found to be 1.77 Ω, corresponding to good ionic conductivity of the

**111**

**Table 1.**

**Figure 5.**

*from Elsevier. Copyright 2018)*[23.]

CrN/activated carbon nanoparticles

**Sample Method Electrolyte** 

CrN thin film Sputtering 0.5 M H2SO4 12.8 mF/cm2

Chemical method

*CrN Sputtered Thin Films for Supercapacitor Applications*

*(a) CV curve of CrN working electrode and steel current collector at 200 mV/s, (b) CV curve of CrN working electrode at different scan rates, (c) specific capacitance vs. scan rate graph, (d) capacitive retention curve of CrN thin film working electrode, (e) Nyquist plot (inset shows the enlarged Nyquist plot at the high frequency region), and (f) corresponding equivalent circuit model. (Adapted from Mohd. Arif et al., with permission* 

**specific**

CrN thin films Sputtering 1 M Na2SO4 41.6 F/g at 5 mV/s This work

*Comparison of the specific capacitance of chromium nitride-based supercapacitor electrodes reported in the literature. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

**Capacitance References**

[17]

at

1 mA/cm2

1 M LiPF6 50 F/g at 1 mV/s [19]

*DOI: http://dx.doi.org/10.5772/intechopen.81469*

#### **Figure 5.**

*Science, Technology and Advanced Application of Supercapacitors*

The EIS spectroscopy of CrN working electrode was measured between the frequency range of 0.01 and 100 kHz. As depicted in **Figure 5e**, the Nyquist plot of CrN working electrode showed a straight line in low frequency range, which represents the diffusion of ions at the electrode-electrolyte interface [22]. The Nyquist plot of CrN working electrodes showed a semicircle in high frequency range, which represents the electronic resistance and contact resistance between active material and current collector (inset of **Figure 5e**). The equivalent circuit model of working electrode is shown in **Figure 5f**. From the EIS circuit model, the electrolyte resistance (Rs) was found to be 1.77 Ω, corresponding to good ionic conductivity of the

*(a and b) FE-SEM images of CrN thin film at different scales, 200 and 100 nm scales, and (c) EDS spectrum of CrN thin film. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

*(a) XPS spectra of N1 s, and (b) XPS spectra of Cr2p3/2. (Adapted from Mohd. Arif et al., with permission* 

**110**

**Figure 4.**

**Figure 3.**

*from Elsevier. Copyright 2018)*[23].

*(a) CV curve of CrN working electrode and steel current collector at 200 mV/s, (b) CV curve of CrN working electrode at different scan rates, (c) specific capacitance vs. scan rate graph, (d) capacitive retention curve of CrN thin film working electrode, (e) Nyquist plot (inset shows the enlarged Nyquist plot at the high frequency region), and (f) corresponding equivalent circuit model. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23.]


#### **Table 1.**

*Comparison of the specific capacitance of chromium nitride-based supercapacitor electrodes reported in the literature. (Adapted from Mohd. Arif et al., with permission from Elsevier. Copyright 2018)*[23].

electrolyte. The charge transfer resistance (Rct) was found to be 6.15 Ω, owing to the contact between CrN film and steel substrate.
