Cadmium selenide microspheres as an electrochemical supercapacitor

Materials Today Chemistry 4 (2017) 164e171

Contents lists available at ScienceDirect

Materials Today Chemistry journal homepage: www.journals.elsevier.com/materials-today-chemistry/

Cadmium selenide microspheres as an electrochemical supercapacitor Sachin A. Pawar*, Dipali S. Patil, Jae Cheol Shin* Department of Physics, Yeungnam University, Gyeongsan, Gyeongbuk 38541, South Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 March 2017 Received in revised form 12 April 2017 Accepted 12 April 2017

This paper reports the synthesis of cadmium selenide electrodes by simple and cost effective chemical bath deposition method for the electrochemical supercapacitors. In order to study the effect of deposition time onto the morphological and electrochemical performance of CdSe electrodes, the reaction time was varied from 2 h to 10 h. As the reaction time goes on increasing the voide-less uniform growth of the thin films with increased size and density of CdSe microspheres is observed from field emission microscopy study. The supercapacitive behavior of the prepared electrodes were analysed with the help of electrochemical impedance, cyclic voltammetry and charge/discharge measurements. The areal capacitance is found to increase from 0.30 mFcm
2 to 1.285 mFcm
2 with respect to the deposition time, this indicates the positive effect towards the electrochemical performance. © 2017 Elsevier Ltd. All rights reserved.

Keywords: CdSe Annealing Chemical bath deposition (CBD) Supercapacitor XPS

1. Introduction The ever increasing demand of energy consumption nowadays have lead the researchers around the globe to seek ecofriendly and long lasting energy harvesting and storage alternatives. Supercapacitors are the new class of energy storage devices owing to its characteristics like high power density, long cycle life and superior safety. The capacitance of supercapacitors is mainly dependent on the electrode materials [1e6]. There are three classes of materials utilized for supercapacitors: namely carbon materials, metal oxides/hydroxides and conducting polymers [7e10]. Compared to metal oxides and conducting polymers, metal sulfides and selenides are abundant and cheap due to the surplus existence of minerals in the nature. Various metal sulfides have been used as an electrode materials for supercapacitors [11e13] but metal selenides are quite rarely studied for this purpose [14e16]. The members two-dimensional (2D) layered metal chalcogenides (LMCs), exhibit unique electronic structures and physical properties due to their special geometric structures with weak interlayer Van der Waals coupling, variable composition, and rich phase structure [14] and thus provide a large library of materials for potential applications in energy storage devices. Supercapacitors are mainly of two types based on their energy storage mechanisms

* Corresponding authors. E-mail addresses: [email protected] (S.A. Pawar), [email protected] (J.C. Shin). http://dx.doi.org/10.1016/j.mtchem.2017.04.002 2468-5194/© 2017 Elsevier Ltd. All rights reserved.

e.g., electrochemical double layer capacitors (EDLC's) and pseudocapacitors. In the first case the capacitance arises due to the charge separation at the electrode/electrolyte interface. Various carbon based materials are used for the EDLC's application. The pseudocapacitance arises from the surface faradaic redox reactions between electrolytes and electrode materials [17,18]. Conducting polymers, and transition metal oxides are the best candidates which can be used for pseudocapacitor applications [19e21]. Cadmium selenide (CdSe) belongs to II-VI group compound semiconductor and is widely used in the field of optoelectronics light-emitting diodes, solar cells, laser diodes, Schottky diodes, biomedical imaging devices, and various kinds of sensors etc. [12e27]. However, CdSe for supercapacitor is studied merely by Bae et al. [28]. Here they used complex hot injection method to synthesize CdSe quantum dots (QDs) and subsequently drop-casted these QDs onto ITO as a 2D thin film. This involves several steps to prepare a CdSe thin film. Several different physical and chemical techniques are currently used to grow CdSe thin films. The present work deals with a simple, one pot CBD deposition of CdSe thin films directly on the stainless steel substrate without intermediate steps in between. The effect of reaction time on the structural, morphological and electrochemical properties of the resulting films is carried out. We found significant changes in the morphological features of CdSe thin films produced by the varying reaction time. The supercapacitive behavior of the CdSe thin films were analysed with the help of electrochemical impedance, cyclic voltammetry and charge/discharge measurements. Enhanced

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

165

Fig. 1. Growth mechanism and different growth stages of CdSe pebbles.

electrochemical performance is observed with respect to varied reaction time. We characterized the thin films using various tools: FE-SEM, XPS and electrochemical measurements.

and CdSe-10h, respectively. The samples were annealed in argon at a temperature of 300  C for 1 h.

2. Experimental details

2.1.1. Growth mechanism The precipitation of metal chalcogenides in CBD occurs only when the ionic product exceeds the solubility product of metal chalcogenides. The overall chemical reactions for the preparation of CdSe microstructures proceed in the following way

2.1. Thin film deposition

Cd2þ þ 4NH3 /CdðNH3 Þ2þ 4

(1)

CdSe thin films were prepared as described in our previous work [29]. Briefly, CdSe thin films were deposited on stainless steel and F:SnO2 (FTO) substrates by CBD using cadmium sulphate (CdSO4.xH2O) as a precursor for Cd, 25 vol% NH4OH as a complexing agent, and sodium selenosulphate (Na2SeSO3-Selenourea) purchased from Aldrich as a Se source. All chemicals used were of analytical grade and did not require further purification. The ready-made Na2SeSO3 solution used as it is. For deposition of CdSe by CBD, an aqueous solution of 0.1 M CdSO4.xH2O in 30 ml was poured into a 100 ml beaker, then 30 ml 25 vol% NH4OH was slowly added with constant stirring, so that the solution was maintained at a pH of ~11. The solution became milky and turbid after addition of ammoniacal solution in cadmium precursor at room temperature because of the formation of Cd(OH)2. Excess addition of ammonia leads to a clear and transparent solution. Finally, 30 ml 0.1 M Na2SeSO3 is added to the solution, which then undergoes a colour change from transparent to light yellow. The temperature of the bath was kept constant at 70  C and deposition was allowed to occur for 2, 4, 6, 8 and 10 h. The substrates were then removed from the bath, rinsed thoroughly using double distilled water, and kept at room temperature for air drying; this sample is herein referred to as CdSe-2h, CdSe-4h, CdSe-6h, CdSe-8h

Na2 SeSO3 þ 2OH
/2NaOH þ SeSO2
3

(2)


2
2
SeSO2
3 þ 2OH 4SO4 þ H2 O þ Se

(3)

The film growth takes place via ion-by-ion condensation of the Cd2þ and Se2
(as shown in Fig. 1) or by adsorption of colloidal particles from the solution onto the substrate;

Cd2þ þ Se2
/CdSe

(4)

Hence, the overall chemical reaction is given as; 2

2
Cd ðNH3 Þ2þ 4 þ SeSO3 þ 2OH /CdSe þ 4NH3 þ SO4 þ H2 O

(5)

2.2. Characterizations of electrodes X-ray photoelectron spectroscopy (XPS, K-alpha, Thermo Scientific, UK) was performed to determine the surface chemical composition. The surface morphology of the films was examined by

166

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

Fig. 2. (a) FE-SEM surface images for samples CdSe-2h, CdSe-4h, CdSe-6h, CdSe-8h and CdSe-10h at magnifications X 10000 (b) FE-SEM cross-sectional images for samples CdSe-8h and CdSe-10h at magnifications X 10000.

field emission scanning electron microscopy (FE-SEM, S-4800 HITACHI, Ltd., Japan). The electrochemical measurements, such as CV, electrochemical impedance and galvanostatic charge/discharge

were taken in a 0.1 M H2SO4 electrolyte in a conventional three electrode arrangement comprised of a graphite counter electrode and a saturated calomel electrode (SCE) serving as the reference

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

Fig. 3. High-resolution XPS spectra of (a) the Cd(3d) (left panel) and (b) Se(3d) (right panel) core levels of the sample CdSe-8h. The XPS spectra are decomposed via Voigt curve fitting.

electrode, using (WonAtech).

a

ZIVE

SP5

electrochemical

workstation

3. Results and discussion Fig. 2(a) shows FE-SEM surface images of CdSe thin films at 10000 magnifications. The samples are well covered with microspheres with voids. A careful look at the micrographs of CdSe microspheres of samples CdSe-2h to CdSe-10h, it is clearly seen that the density and size of microspheres goes on increasing as the reaction time is increased from 2 h to 10 h. The density of microspheres is maximum for sample CdSe-8h. The samples prepared with the reaction time 2 h and 4 h have uneven distribution of microspheres and there is a presence of larger voids in between the microspheres. The average size of these microspheres is found to be 300 nm. The size of microspheres goes on increasing as the reaction time increases owing to the larger amount of material deposition. Therefore, in sample CdSe-6h and CdSe-8h the size of the microspheres is

167

almost doubled and it is found to be 600 nm. This resulted into the voide-less uniform thin film. Finally for sample CdSe-10h, the microspheres could not retain it's shape as that of the previous samples instead those uniform sized microspheres have flattened to become a complete 2 D layer. Though, some overgrowth of flat larger microspheres is observed. A similar CdSe microstructure was reported by Kale et al., who also used a CBD method [30]. Zhao et al. observed formation of CdSe spherical nanoparticles using CBD [31]. They studied the effect of ammonia concentration on the diameter and density of CdSe nanoparticles. In order to check the effect of CBD reaction time on the thickness of CdSe samples we did the cross-sectional FESEM measurements of the samples CdSe-8h and CdSe-10h (Fig. 2 (b)). For cross-sectional FESEM analysis the CdSe thin films were grown on FTO substrates instead of steel substrates as the latter sufferes from bending while sample preparations. It is noted that for sample CdSe-8h, the thickness of CdSe thin film is ~850 nm. Whereas for sample CdSe-10 h it is difficult to measure the thickness of CdSe thin film. This is due to 10 h reaction time of the CBD resulted into delamination of CdSe thin films from the surface of sample CdSe-10h. The stoichiometric and bonding changes in CdSe thin films was studied using XPS. All data were corrected for electrostatic charging using C 1s as a reference. Fig. 3(a) and (b) illustrate the Cd(3d) (left panel) and Se(3d) (right panel) high-resolution XPS spectra obtained for sample CdSe-8h. Fig. 3(a) shows a double peak in the Cd(3d) spectra in CdSe-8h sample, particularly Cd(3d5/2) peak at 405.27 eV and Cd(3d3/2) peak at 412.08 eV suggests that Cd exists either in metallic form or in CdSe form [32]. There is no splitting of double peak features of CdSe is observed in the XPS which indicates only Cd is present on the surface and there is no evidence for CdO formation in the CdSe sample affirming the high purity of our sample [29]. The energy separation between these two peaks is 6.81 eV, which is akin to that observed in CdSe nanocrystals by Hou et al. [33]. Similarly, Fig. 3(b) shows Se(3d) binding energy peak at 54.35 eV confirms presence of CdSe phase only [34]. No extra peak was observed in the decomposed XPS spectra of Cd(3d) and Se(3d), which indicates a lack of formation of CdO and SeO2 (or SeOx) was observed during synthesis. This clearly indicates that the microspheres consisted of only the elements Cd and Se and not their oxides. Electrochemical impedance spectroscopy (EIS) provides useful information on the redox reaction resistance and equivalent series resistance. In this study, impedance measurements were carried out over the frequency range, 1 to 1  105 Hz. Fig. 4(a) presents the Nyquist plots obtained at the open circuit potential for all samples (CdSe-2h to CdSe-10h) in a three electrode cell configuration in an aqueous solution of 0.1 M H2SO4. Inset of Fig. 4 represents the magnified view of Nyquist plot. At high frequency region, the intercept of the curve at real axis indicates the resistance of the electrochemical system (Rs) which includes the inherent resistance of the electroactive, ionic resistance of electrolyte and contact resistance at the interface between electrolyte and electrode. Rs of the samples CdSe-2h to CdSe-8h decreased from 0.61 U to 0.35 U. A decrease in Rs with increase in reaction time indicates an increase in the conductivity of the prepared electrode [35], because of the voide-less growth of the thin films with increased density of CdSe microspheres. Further increment in reaction time up 10 h (CdSe-10h) increase in Rs (0.42 U) was observed. This is due to the rising the reaction time beyond 8 h causes the peeling off the film which leads to reduction in the conductivity of the electrode. In order to support this we performed the cross-sectional FESEM measurements of samples CdSe-8h and CdSe-10h which is shown in Fig. 2(b). It is evident from Fig. 2(b) that the thicknesses of the samples CdSe-8h and CdSe-10h differes from each other. The inset in Fig. 4 displays a simple equivalent

168

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

Fig. 4. (a) Nyquist plot (b) Log (F) Vs phase angle (c) Log (F) Vs Log jZj of all samples in 0.1 M H2SO4 electrolyte.

Table 1 Various supercapacitor parameters obtained for the prepared electrodes are summarized in the table. Sample Code

Rs ( U)

Rct (kU)

Areal capacitance (mFcm
2)

CdSe-2h CdSe-4h CdSe-6h CdSe-8h CdSe-10 h

0.60 0.46 0.42 0.35 0.43

919.66 702.17 266.80 157.23 210.60

0.30 0.885 0.975 1.285 0.915

The bold values indicate the optimized sample.

circuit which fits well to these experimental Nyquist plots. This equivalent circuit consist of electrolyte resistance (Re), charge transfer resistance (Rct) which describe the charge transfer kinetics of the electrons, constant phase element (Q) and warburge element (W) [17,36]. The Rct of the sample goes on decresing (from 919.66 kU to 157.23 kU) with increasing reaction time from 2 h to 8 h, further increase in reaction time up to 10 h Rct increases. The Rs and Rct values of all prepared electrodes obtained from EIS study are summarized in Table 1. From this it was observed that the sample CdSe-8h demonstrates the lower Rs (0.35 U) and Rct (157.23 kU) values as compared to other samples. In Fig. 4(b) and (c), the logarithm of the modulus, jZj (Fig. 4(b)) and the phase (ф) (Fig. 4(c)), are plotted against the logarithm of the frequency, F, for all the samples. This demonstrates the frequency

versus magnitude is linear (on the log-log bode plot) and phase angle approaches to
90 . In the phase angle plot, the phase angle approaching to the negative 90 at low frequency usually describes the pure capacitive behavior of the electrode [37]. In order to get the optimized electrochemical performance of the electrodes, Cyclic voltammetry (CV) and charge e discharge measurements of all the prepared electrodes were carried out. CVs of all the samples were recorded from
0.2 to þ0.8 V versus SCE at different scan rates (10 mVs
1 to 100 mVs
1) in 0.1 M H2SO4 [Fig. 5(aee)]. The CV of all samples display the nonrectangular shape indicates the pseudocapacitive nature of all samples where the faradiac reversible reactions occur onto the electrode surface. The CV curves of all CdSe samples display the pseudo-capacitive behavior with a one pair of well-broaden redox peaks. As the reaction time increases from 2 h to 8 h the current goes on increasing, whereas the current decreases for the sample deposited with 10 h reaction time. This increase in current from sample CdSe-2h to CdSe-8h is due to reduction in Rs and Rct values with respect to increase in reaction time (Table 1). The areal capacitance of all the electrodes was calculated from CV curves using following equation:

Z idv CA ¼

2A  △V  S

(1)

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

169

Fig. 5. Cyclic voltammograms of samples (a) CdSe-2h, (b) CdSe-4h, (c) CdSe-6h, (d) CdSe-8h and (e) CdSe-10 h within a potential window
0.2 to þ0.8 V versus SCE at different scan rates in 0.1 M H2SO4 electrolyte.

Fig. 6. (a) Variation of areal capacitance with respect to reaction time. (b) Variation of areal capacitance with respect to scan rate.

where CA (Fcm
2) is the areal capacitance, !idV (A) is the integrated area of the CV curve, A (cm2) is the area of the electrode, △V (V) is the potential range, and S (Vs
1) is the scan rate. The plot of areal capacitance with respect to reaction time is shown in Fig. 6(a). As the reaction time increases (From 2 h to 10 h) the areal capacitance increases from 0.30 to 1.285 mFcm
2; with further increment in the reaction time (at 10 h) there is decrease in areal capacitance (0.9152 mFcm
2) was observed. This increased and decreased capacitance with respect to time is correlated with the Rs and Rct which was reflected in Table 1. The variation of areal capacitance with respect to scan rate for CdSe-8h is as shown in Fig. 6(b). This presented the typical limited rate performance of supercapacitors, which is increased capacitance with decreasing

scan rates. It was observed that the areal capacitance about 1.285 mFcm
2 at 10 mVs
1 is decreased down to 0.418 mFcm
2 at 100 mVs
1 in case of CdSe-8h. Fig. 7 shows the galvanostatic charge/discharge plots of all the electrodes at a 0.2 mA applied current over the potential range between 0.0 and þ 0.8 V versus SCE using 0.1 M H2SO4 as an electrolyte. From this it was observed that the highest discharge time obtained for CdSe-8h. The energy density of CdSe-8h was calculated from the charge discharge curves using equations as mentioned in our previous reports [38,39]. The energy density of 4.015 Whkg
1 is achieved for CdSe-8h at 0.2 mA applied current. Above supercapacitive parameters (areal capacitance (1.285 mFcm
2) and Energy density (4.015 Whkg
1)) revealed that,

170

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171

reaction time showed superior supercapacitive performance with 1.285 mFcm
2 areal capacitance and 4.015 WhKg
1 energy density, due to the lower values of Rs and Rct obtained for this electrode. These new electrode material based on CdSe can bring new approach towards the metal selenide based energy storage devices. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF-2017R1C1B2010906). References

Fig. 7. Galvanostatic charge/discharge characteristics of all samples at 0.2 mA applied current in 0.1 M H2SO4 electrolyte.

Fig. 8. Capacitance retention and areal capacitance as a function of the cycle number.

CdSe-8h electrode is better choice for the supercapacitor as compared to the other electrodes. Further the cyclic stability of the CdSe-8h electrode was studied upto 2000 cycles by recording CV at 10 mVs
1. Fig. 8 displays the capacitance retention and areal capacitance of CdSe-8h has changed along with the number of cycles. This indicates that the areal capacitance of the electrode is 1.285 Fcm
2 for the first cycle, which decreases slowly to 1.124 Fcm
2, i.e., approximately 12.5% loss is observed after 1000 cycles, but only 3.8% loss was observed for the next 1000 cycles. This decreasing trend suggests that the optimized electrode becomes more stable with increasing number of cycles. 4. Conclusions Cadmium selenide thin films were deposited onto stainless steel substrate by simple CBD for supercapacitor application. The effect of reaction time on the electrochemical performance of CdSe were studied to achieve the excellent electrode. The Phase angle (ф) and modulus, jZj vesus frequency plots revealed the ideal capacitive behavior of the prepared electrodes. The CdSe deposited with 8 h

[1] A. Sanchez-Sanchez, T.A. Centeno, F. Suarez-García, A. Martínez-Alonso, J.M.D. Tascon, The importance of electrode characterization to assess the supercapacitor performance of ordered mesoporous carbons, Micropor. Mesopor. Mat. 235 (2016) 1e8. [2] V. Velmurugan, U. Srinivasarao, R. Ramachandran, M. Saranya, A.N. Grace, Synthesis of tin oxide/graphene (SnO2/G) nanocomposite and its electrochemical properties for supercapacitor applications, Mater. Res. Bull. 84 (2016) 145e151. [3] H. Zhang, H. Su, L. Zhang, B. Zhang, F. Chun, X. Chu, W. He, W. Yang, Flexible supercapacitors with high areal capacitance based on hierarchical carbon tubular nanostructures, J. Power Sources 331 (2016) 332e339. [4] P. Zhou, L. Fan, J. Wu, C. Gong, J. Zhang, Y. Tu, Facile hydrothermal synthesis of NiTe and its application as positive electrode material for asymmetric supercapacitor, J. Alloy. Compd. 685 (2016) 384e390. [5] M. Balasubramaniam, S. Balakumar, Exploration of electrochemical properties of zinc antimonate nanoparticles as supercapacitor electrode material, Mat. Sci. Semicon. Proc. 56 (2016) 287e294. [6] S. Nagamuthu, S. Vijayakumar, S.H. Lee, K.S. Ryu, Hybrid supercapacitor devices based on MnCo2O4 as the positive electrode and FeMn2O4 as the negative electrode, Appl. Surf. Sci. 390 (2016) 202e208. [7] K. Wang, M. Xu, Y. Gu, Z. Gu, Q.H. Fan, Symmetric supercapacitors using ureamodified lignin derived N-doped porous carbon as electrode materials in liquid and solid electrolytes, J. Power Sources 332 (2016) 180e186. [8] M. Lia, J.P. Chenga, J. Wang, F. Liu, X.B. Zhang, The growth of nickel-manganese and cobalt-manganese layered double hydroxides on reduced graphene oxide for supercapacitor, Electrochim. Acta 206 (2016) 108e115. [9] N. Wang, P. Zhao, K. Liang, M. Yao, Y. Yang, W. Hu, CVD-grown polypyrrole nanofilms on highly mesoporous structure MnO2 for high performance asymmetric supercapacitors, Chem. Eng. J. 307 (2017) 105e112. [10] D.S. Patil, S.A. Pawar, J. Hwang, J.H. Kim, P.S. Patil, J.C. Shin, Silver incorporated PEDOT: PSS for enhanced electrochemical performance, J. Ind. Eng. Chem. 42 (2016) 113e120. [11] Z. Jiang, W. Lu, Z. Li, K.H. Ho, X. Li, X. Jiao, D. Chen, Synthesis of amorphous cobalt sulfide polyhedral nanocages for high performance supercapacitors, J. Mater. Chem. A 2 (2014) 8603e8606. [12] F. Luoa, J. Lia, H. Yuanb, D. Xiao, Rapid synthesis of three dimensional flowerlike cobalt sulfide hierarchitectures by microwave assisted heating method for high-performance supercapacitors, Electrochim. Acta 123 (2014) 183e189. [13] W. Wei, L. Mi, Y. Gao, Z. Zheng, W. Chen, X. Guan, Partial ion-exchange of nickel-sulfide-derived electrodes for high performance supercapacitors, Chem. Mater 26 (2014) 3418e3426. [14] C. Zhang, H. Yin, M. Han, Z. Dai, H. Pang, Y. Zheng, Y.Q. Lan, J. Bao, J. Zhu, Twodimensional tin selenide nanostructures for flexible all-solid-state supercapacitors, ACS Nano 8 (2014) 3761e3770. [15] A. Banerjee, S. Bhatnagar, K.K. Upadhyay, P. Yadav, S. Ogale, Hollow Co0.85Se nanowire array on carbon fiber paper for high rate pseudocapacitor, ACS Appl. Mater. Interfaces 6 (2014) 18844e18852. [16] X. Wang, B. Liu, Q. Wang, W. Song, X. Hou, D. Chen, Y.B. Cheng, G. Shen, Threedimensional hierarchical GeSe2 nanostructures for high performance flexible all-solid-state supercapacitors, Adv. Mater 25 (2013) 1479e1486. [17] Dipali S. Patil, Sachin A. Pawar, Jin Hyeok Kim, Pramod S. Patil, Jae Cheol Shin, Electrochim. Acta 213 (2016) 680e690. [18] D.S. Patil, S.A. Pawar, R.S. Devan, S.S. Mali, M.G. Gang, Y.R. Ma, C.K. Hong, J.H. Kim, P.S. Patil, Polyaniline based electrodes for electrochemical supercapacitor: synergistic effect of silver, activated carbon and polyaniline, J. Electroanal. Chem. 724 (2014) 21e28. [19] P. Simon, Y. Gogotsi, Materials for electrochemical capacitors, Nat. Mater 7 (2008) 845e854. [20] G. Wang, L. Zhang, J. Zhang, A review of electrode materials for electrochemical supercapacitors, Chem. Soc. Rev. 41 (2012) 797e828. [21] M. Zhi, C. Xiang, J. Li, M. Li, N. Wu, Nanostructured carbon-metal oxide composite electrodes for supercapacitors: a review, Nanoscale 5 (2013) 72e88. [22] F. Li, W.N. Li, S.Y. Fu, H.M. Xiao, Formulating CdSe quantum dots for white light-emitting diodes with high color rendering index, J. Alloy. Compd. 647 (2015) 837e843.

S.A. Pawar et al. / Materials Today Chemistry 4 (2017) 164e171 [23] P.P. Hankare, P.A. Chate, D.J. Sathe, M.R. Asabe, B.V. Jadhav, Photoelectrochemical studies of CdSe thin films deposited by dip method, J. Alloy. Compd. 474 (2009) 347e350. [24] K. Ohkuno, H. Oku, Y. Araki, N. Nagata, J. Saraie, Fabrication of high-quality CdSe quantum dots for green laser diodes by molecular beam epitaxy, J. Cryst. Growth 301e302 (2007) 755e758. [25] Y. Zhang, L. Du, Y. Lei, H. Zhao, Construction of high-quality CdSe NB/graphene Schottky diodes for optoelectronic applications, Mater. Lett. 131 (2014) 288e291. [26] X. Ji, F. Peng, Y. Zhong, Y. Su, Y. He, Fluorescent quantum dots: synthesis, biomedical optical imaging, and biosafety assessment, Colloid. Surf. B 124 (2014) 132e139. [27] R. Ke, X. Zhang, L. Wang, C. Zhang, S. Zhang, C. Mao, H. Niu, J. Song, B. Jin, Y. Tian, Electrochemiluminescence sensor based on Graphene Oxide/Polypyrrole/CdSe nanocomposites, J. Alloy. Compd. 622 (2015) 1027e1032. [28] J. Bae, U. Paik, D.K. Yi, Novel semiconducting CdSe quantum dot based electrochemical capacitors, Mater. Lett. 162 (2016) 230e234. [29] S.A. Pawar, D.S. Patil, M.P. Suryawanshi, U.V. Ghorpade, A.C. Lokhande, J.Y. Park, R.B.V. Chalapathy, J.C. Shin, P.S. Patil, J.H. Kim, Effect of different annealing environments on the solar cell performance of CdSe pebbles, Acta Mate 108 (2016) 152e160. [30] R.B. Kale, S.Y. Lu, Air annealing induced transformation of cubic CdSe microspheres into hexagonal nanorods and micro-pyramids, J. Alloy. Compd. 640 (2015) 504e510. [31] Y. Zhao, Z. Yan, J. Liu, A. Wei, Synthesis and characterization of CdSe nanocrystalline thin films deposited by chemical bath deposition, Mate. Sci. Semicon. Pro 16 (2013) 1592e1598.

171

[32] M. Azad Malik, N. Revaprasadu, P. O'Brien, Air-stable single-source precursors for the synthesis of chalcogenide semiconductor nanoparticles, Chem. Mater 13 (2001) 913. [33] J. Hou, H. Zhao, F. Huang, Q. Jing, H. Cao, Q. Wu, S. Peng, G. Cao, High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays, J. Power Sources 325 (2016) 438e445. [34] Q. Yang, K. Tang, F. Wang, C. Wang, Y. Qian, A g-irradiation reduction route to nanocrystalline CdE (E¼Se, Te) at room temperature, Mater. Lett. 57 (2003) 3508. [35] C. Zhou, Y. Zhang, Y. Li, J. Liu, Construction of high-capacitance 3D CoO@ Polypyrrole nanowire array electrode for aqueous asymmetric supercapacitor, Nano Lett. 13 (2013) 2078e2085. [36] Q. Zheng, H. Wu, Z. Shen, W. Gao, Y. Yu, Y. Ma, W. Guang, Q. Guo, R. Yan, J. Wan, K. Ding, An electrochemical DNA sensor based on polyaniline/graphene: high sensitivity to DNA sequences in a wide range, Analyst 140 (2015) 6660. [37] D.W. Wang, F. Li, H.T. Fang, M. Liu, G.Q. Lu, H.M. Cheng, Effect of pore packing defects in 2-d ordered mesoporous carbons on ionic transport, J. Phys. Chem. B 110 (2006) 8570e8575. [38] D.S. Patil, J.S. Shaikh, S.A. Pawar, R.S. Devan, Y.R. Ma, A.V. Moholkar, J.H. Kim, R.S. Kalubarme, C.J. Park, P.S. Patil, Investigations on silver/polyaniline electrodes for electrochemical supercapacitors, Phys. Chem. Chem. Phys. 14 (2012) 11886e11895. [39] D.S. Patil, S.A. Pawar, R.S. Devan, M.G. Gang, Y.R. Ma, J.H. Kim, P.S. Patil, Electrochemical supercapacitor electrode material based on polyacrylic acid/ polypyrrole/silver composite, Electrochim. Acta 105 (2013) 569e577.