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Fig. 5. (a) and (b)Energy Band gap evaluation of synthesized samplesA1 and A2 using Kubelka—Munk samples Al and A2 show type IV isotherm with H3 hysteresis at relative pressure (P/P,) ranging from 0.0 to 1.0 which indicate that the syn- thesized samples Al and A2 are mesoporous materials [30]. Surface area of the samples were evaluated using Brunauer-Emmett-Teller (BET) method Eq. (7). Surface area of samples Al and A2 are 6.42 m?/ g and 8.32 m?/g, respectively. Pore diameter of the samples Al and A2 are 2.47 cm?/g, 2.12 cm?/g, which are calculated from BJH (Barrett-Joy- ner-Halenda) method [31]. High surface areas provide more electro- active site for catalytic activities [32].Porosity play a pivotal role in the electro-catalytic performance of the nano-material, porous surfaces reduce the diffusion resistance and large pore size easily absorb the electrolyte ions on the surface of the electrode which enhances electro-catalytic performance [33]. samples Al and A2 show strong reflectance peaks around 340 nm, and 330 nm, respectively which are shown in inset of Fig. 5(a) and (b) [35]. For exact calculation of energy band gap, reflectance was evaluated by Kubelka- Munk function Eq. (11). For calculation of band gap, the graph is plotted between the [F(Rq)hv] V/ and ho extrapolating the straight line at [F(R.)hv]/" = 0, gives the value of band gap, where ‘n’ repre- sents the nature of transition. The ‘n’ takes different value such as n = 1/2 for allowed direct band gap and n = 2 for allowed indirect band gap [36,37]. Nickel sulphide show indirect energy band gap, so n = 2 is taken [38]. The intercept of [F (Rq) hv]? and ho gives the value of en- ergy band gap, as shown in Fig. 5(a) and (b). The energy band gap of the synthesized samples Al and A2 are 2.75 nm, 3.46 nm, respectively [39].

Figure 5 (a) and (b)Energy Band gap evaluation of synthesized samplesA1 and A2 using Kubelka—Munk samples Al and A2 show type IV isotherm with H3 hysteresis at relative pressure (P/P,) ranging from 0.0 to 1.0 which indicate that the syn- thesized samples Al and A2 are mesoporous materials [30]. Surface area of the samples were evaluated using Brunauer-Emmett-Teller (BET) method Eq. (7). Surface area of samples Al and A2 are 6.42 m?/ g and 8.32 m?/g, respectively. Pore diameter of the samples Al and A2 are 2.47 cm?/g, 2.12 cm?/g, which are calculated from BJH (Barrett-Joy- ner-Halenda) method [31]. High surface areas provide more electro- active site for catalytic activities [32].Porosity play a pivotal role in the electro-catalytic performance of the nano-material, porous surfaces reduce the diffusion resistance and large pore size easily absorb the electrolyte ions on the surface of the electrode which enhances electro-catalytic performance [33]. samples Al and A2 show strong reflectance peaks around 340 nm, and 330 nm, respectively which are shown in inset of Fig. 5(a) and (b) [35]. For exact calculation of energy band gap, reflectance was evaluated by Kubelka- Munk function Eq. (11). For calculation of band gap, the graph is plotted between the [F(Rq)hv] V/ and ho extrapolating the straight line at [F(R.)hv]/" = 0, gives the value of band gap, where ‘n’ repre- sents the nature of transition. The ‘n’ takes different value such as n = 1/2 for allowed direct band gap and n = 2 for allowed indirect band gap [36,37]. Nickel sulphide show indirect energy band gap, so n = 2 is taken [38]. The intercept of [F (Rq) hv]? and ho gives the value of en- ergy band gap, as shown in Fig. 5(a) and (b). The energy band gap of the synthesized samples Al and A2 are 2.75 nm, 3.46 nm, respectively [39].

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Synthesis parameters of the B-NiS nanoparticles. Table 1 Rhombohedral f-NiS and their electro-catalytic performance. Carbona- ceous free electrode is used for the electrochemical studies in 1 M LiOH aqueous electrolyte. The synthesized B-NiS nanoparticles were charac- terized by, HR-XRD, UV-Vis diffuse reflectance spectroscopy, BET, FTIR, FESEM.
Synthesis parameters of the B-NiS nanoparticles. Table 1 Rhombohedral f-NiS and their electro-catalytic performance. Carbona- ceous free electrode is used for the electrochemical studies in 1 M LiOH aqueous electrolyte. The synthesized B-NiS nanoparticles were charac- terized by, HR-XRD, UV-Vis diffuse reflectance spectroscopy, BET, FTIR, FESEM.
Fig. 1. Rietveld refinement pattern of XRD data of synthesized samples Al and A2. Red colour shows the refined data. Vertical green line show the Bragg's position of the rhombohedral phase of B-NiS. Cyan line shows the difference between refined data and observed data.(*) marked peaks represents the presence of Ni(OH)», (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
Fig. 1. Rietveld refinement pattern of XRD data of synthesized samples Al and A2. Red colour shows the refined data. Vertical green line show the Bragg's position of the rhombohedral phase of B-NiS. Cyan line shows the difference between refined data and observed data.(*) marked peaks represents the presence of Ni(OH)», (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
Parameters are calculated from Rietveld Refinement analysis. Table 2
Parameters are calculated from Rietveld Refinement analysis. Table 2
Fig. 2. FTIR spectra of the synthesized sample Al and A2.
Fig. 2. FTIR spectra of the synthesized sample Al and A2.
Fig. 3. FESEM image of the synthesized samples Al(a,c) and A2 (b,d).
Fig. 3. FESEM image of the synthesized samples Al(a,c) and A2 (b,d).
Peak positions of vibrational bands of synthesized Samples Al and A2. Table 3
Peak positions of vibrational bands of synthesized Samples Al and A2. Table 3
Parameters which are calculated from N2 adsorption-desorption isotherm. Table 4 Thiourea (SC (NH2)2) was used as sulphur source which play a vital role in the formation of B-NiS. Thiourea decomposes at 140 C and pro- duced H2S, 2NH3 and CO.. Through hydrolysis S?~ ions released which originated from thiourea. These S?- ions reacted with [Ni(NH3)4]?* and led to the formation of B-NiS.
Parameters which are calculated from N2 adsorption-desorption isotherm. Table 4 Thiourea (SC (NH2)2) was used as sulphur source which play a vital role in the formation of B-NiS. Thiourea decomposes at 140 C and pro- duced H2S, 2NH3 and CO.. Through hydrolysis S?~ ions released which originated from thiourea. These S?- ions reacted with [Ni(NH3)4]?* and led to the formation of B-NiS.
Fig. 4. (a) Nitrogen isotherms of synthesized samples A1 and A2 (b) Pore size distribution plot of the synthesized p-NiS (c) BET plot of the synthesized B-NiS. Fourier transform infrared spectra of the synthesized samples Al and A2, are shown in Fig. 2, performed in the wave number range of 400-4000 cm ~!.The characteristics vibrational modes are identified, which are present on the surface of the synthesized samples Al and A2. All observed vibrational bands and wave numbers are provided in Table .3. Broad peaks around at 1060-1150 cm~! and 3400-3450 cm™! are due to the presence of C-O and O-H bonds respectively [24].These peaks indicate the presence of HzO and COz2 on the surface of the syn- thesized samples. Due to saturated alkane, C-N vibration bands are observed at 1300-1380 cm™! in samples Al and A2 respectively [25]. The C-H and S-H vibrational bands are observed at 2900-2940 cm™! The textural properties of the synthesized samples Al and A2 were studied by the Np» adsorption-desorption isotherm. All the parameters were calculated from the N2 adsorption-desorption isotherm is shown in Table .4. According to the shape of the isotherms (Fig. 4(a)), synthesized
Fig. 4. (a) Nitrogen isotherms of synthesized samples A1 and A2 (b) Pore size distribution plot of the synthesized p-NiS (c) BET plot of the synthesized B-NiS. Fourier transform infrared spectra of the synthesized samples Al and A2, are shown in Fig. 2, performed in the wave number range of 400-4000 cm ~!.The characteristics vibrational modes are identified, which are present on the surface of the synthesized samples Al and A2. All observed vibrational bands and wave numbers are provided in Table .3. Broad peaks around at 1060-1150 cm~! and 3400-3450 cm™! are due to the presence of C-O and O-H bonds respectively [24].These peaks indicate the presence of HzO and COz2 on the surface of the syn- thesized samples. Due to saturated alkane, C-N vibration bands are observed at 1300-1380 cm™! in samples Al and A2 respectively [25]. The C-H and S-H vibrational bands are observed at 2900-2940 cm™! The textural properties of the synthesized samples Al and A2 were studied by the Np» adsorption-desorption isotherm. All the parameters were calculated from the N2 adsorption-desorption isotherm is shown in Table .4. According to the shape of the isotherms (Fig. 4(a)), synthesized
Areal capacitance of the synthesized samples Al and A2 at different scan rates. Table 5 slope (m) of the plot is m = 0.5, then the process is diffusion controlled, if slope is m= 1, capacitive behaviour is dominating [43]. Fig. 7 shows that charge storage mechanism in the synthesized samples Al and A2 is diffusion controlled [41,44].
Areal capacitance of the synthesized samples Al and A2 at different scan rates. Table 5 slope (m) of the plot is m = 0.5, then the process is diffusion controlled, if slope is m= 1, capacitive behaviour is dominating [43]. Fig. 7 shows that charge storage mechanism in the synthesized samples Al and A2 is diffusion controlled [41,44].
Fig. 8. Areal capacitance of the synthesized samples Al and A2 at different scan rate. Fig. 7. log (peak current) versus log scan rate which indicated that the syn- thesized samples Al and A2 are diffusion controlled.
Fig. 8. Areal capacitance of the synthesized samples Al and A2 at different scan rate. Fig. 7. log (peak current) versus log scan rate which indicated that the syn- thesized samples Al and A2 are diffusion controlled.
Fig. 6. (a) and (b) Cyclic voltammetry curves of the synthesized samples Al and A2.
Fig. 6. (a) and (b) Cyclic voltammetry curves of the synthesized samples Al and A2.
Electroactive mass of the electrodes Al and A2 before cyclic stability and after cyclic stability.
Electroactive mass of the electrodes Al and A2 before cyclic stability and after cyclic stability.
Electrochemical impedance parameters of the synthesized samples Al and A2 are calculated using Z-fit.
Electrochemical impedance parameters of the synthesized samples Al and A2 are calculated using Z-fit.
Fig. 9. Cyclic stability of the synthesized samples Al and A2 in 1 M LiOH aqueous electrolyte.
Fig. 9. Cyclic stability of the synthesized samples Al and A2 in 1 M LiOH aqueous electrolyte.
Electrochemical impedance measurements were performed to study the charge kinetics, internal resistance and charge transfer resistance of Fig. 10. Nyquist plot synthesized samples (a) Sample Al (b) Sample A2 and (c) Equivalent circuit diagram.
Electrochemical impedance measurements were performed to study the charge kinetics, internal resistance and charge transfer resistance of Fig. 10. Nyquist plot synthesized samples (a) Sample Al (b) Sample A2 and (c) Equivalent circuit diagram.
Fig. 11. Bode plot of the phase angle and log |Z| versus frequency of the synthesized samples (a) Sample Al (b) Sample A2.
Fig. 11. Bode plot of the phase angle and log |Z| versus frequency of the synthesized samples (a) Sample Al (b) Sample A2.
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