- Nano Express
- Open Access
The Two-Dimensional Nanocomposite of Molybdenum Disulfide and Nitrogen-Doped Graphene Oxide for Efficient Counter Electrode of Dye-Sensitized Solar Cells
© Cheng et al. 2016
- Received: 27 August 2015
- Accepted: 25 January 2016
- Published: 29 February 2016
In this study, we reported the synthesis of the two-dimensional (2D) nanocomposite of molybdenum disulfide and nitrogen-doped graphene oxide (MoS2/nGO) as a platinum-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy were used to examine the characteristics of the 2D nanocomposite of MoS2/nGO. The cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and the Tafel polarization measurements were carried out to examine the electrocatalytic abilities. XPS and Raman results showed the 2D behaviors of the prepared nanomaterials. HRTEM micrographs showed the direct evidence of the 2D nanocomposite of MoS2/nGO. The results of electrocatalytic examinations indicated the MoS2/nGO owning the low charge transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide on the electrolyte–electrode interface. The 2D nanocomposite of MoS2/nGO combined the advantages of the high specific surface of nGO and the plenty edge sites of MoS2 and showed the promoted properties different from those of their individual constituents to create a new outstanding property. The DSSC with MoS2/nGO nanocomposite CE showed a photovoltaic conversion efficiency (PCE) of 5.95 % under an illumination of AM 1.5 (100 mW/cm2), which was up to 92.2 % of the DSSC with the conventional platinum (Pt) CE (PCE = 6.43 %). These results reveal the potential of the MoS2/nGO nanocomposite in the use of low-cost, scalable, and efficient Pt-free CEs for DSSCs.
- Molybdenum disulfide
- Graphene oxide
- Counter electrode
- Dye-sensitized solar cells
Dye-sensitized solar cells (DSSCs) are considered as the next-generation solar cells, because of low cost, easy process, and low energy consumption [1–4]. The conventional DSSC is composed of a ruthenium dye-sensitized titanium dioxide (TiO2) working electrode (WE), an electrolyte containing iodine ions, and a platinum (Pt) catalyst counter electrode (CE) . In order to ensure the performance of DSSCs, Pt plays an important catalytic material for DSSCs. However, due to Pt as an expensive and scarce material, it is necessary to find an alternative economical material to replace Pt for profitable DSSCs.
Carbon materials show the advantages of their low cost, high surface area, and high electric conductivity. Recently, low-dimensional carbon nanomaterials, such as carbon nanotubes (CNTs) [5, 6], carbon nanofibers (CNFs) [7, 8], graphene [9–11], and graphene oxide (GO) [9, 12], have been found to replace Pt for DSSCs. Some recent reports have claimed that the performance of carbon nanomaterials in the CE of DSSCs benefited from the presence of the plenty active sites, which may be attributed to the defect sites [7, 11, 12]. GO is an important carbon nanomaterial in the graphene family. In addition, due to their unique two-dimensional (2D) nanostructural feature, high specific surface area, electrochemical stability, and hydrophilic oxygen-containing groups, GO have been widely used as anchored templates to synthesize nanocomposites for DSSC CEs [13, 14]. However, GO suffered relatively high oxygen-containing defects and structural defects such as vacancies and topological defects on the surface. The plenty oxygen-containing defects on the GO surface brought out the low exchange current density, because the surface defects cut down the electrical conductivity . In order to overcome the disadvantages of GO, nitrogen atoms doped into GO to synthesize the nitrogen-doped GO (nGO) were demonstrated to repair the defects, which provided the improvement in the electronic structure of GO . On the other hand, the nitrogen-doped process broadens the electrochemical application area of a variety of carbon-based nanomaterials, including the nitrogen-doped CNT for glucose sensor , the nitrogen-doped reduced graphene oxide (N-rGO) for the DSSC , the nitrogen-doped graphene, and the N-rGO for supercapacitors [19, 20]. Nitrogen-doped carbon-based nanomaterials not only can adjust the work function of graphene  but also can improve the electrical conductivity and the electrochemical properties of the graphene family.
Recently, stimulated by the discovery of the 2D nanomaterial graphene, the transition metal dichalcogenides (TMDCs) with the 2D nanostructure have attracted considerable attention [22–28]. Molybdenum disulfide (MoS2) is a typical TMDC, one unit sheet pile up with three layers which is S–Mo–S arranged sequentially [25, 26]. MoS2 has been found recently with its excellent catalytic activity because their edge planes provided abundant active sites for catalytic reactions [24, 29].
In this study, we synthesized the 2D nanocomposite of molybdenum disulfide and nitrogen-doped graphene oxide (MoS2/nGO) based on the 2D nanomaterials of MoS2 and nGO. Due to the high specific surface of nGO, the nGO was used as the anchored templates to synthesize the MoS2 on the surface as the 2D nanocomposite of MoS2/nGO. The N-doping atoms of nGO not only repaired the vacancies but also replaced the O atoms of GO to enhance the electrical conductivity. In combining the advantages of the high specific surface of nGO with the improving conductivity and the excellent catalytic activity of MoS2, the 2D nanocomposite of MoS2/nGO showed the outstanding electrocatalytic activities. The synthesized MoS2/nGO nanocomposite was used as a CE to assemble into a Pt-free DSSC and examined under the illumination of AM 1.5 (100 mW/cm2). The DSSC with MoS2/nGO nanocomposite CE exhibited the impressive photovoltaic conversion efficiency (PCE, η) of 5.95 %. It was up to 92.2 % compared with the DSSC using the conventional Pt CE (η = 6.43 %). The results showed that MoS2/nGO nanocomposites have great potential for DSSC-related applications and indicated its potential as an alternative to replace Pt.
Synthesis of MoS2/nGO Nanocomposite CE
Three steps were used for preparing the MoS2/nGO nanocomposite CE. In step 1, GO nanosheets were synthesized from natural graphite flakes (Alfa Aesar, Ultra Superior Purity >99.9999 %) by using modified Hummer’s method . In step 2, hydrothermal synthesis method was used to dope nitrogen atoms into GO to obtain nGO nanosheets , 120 mg GO dissolved in 120 mL deionized water, and followed by 1 h of sonication. The as-synthesized GO solution was prepared by using 3 mL ammonia (NH4OH) and 2 mL hydrazine hydrate (N2H4) as the reducing agents. Subsequently, the aforementioned solution was transferred into a Teflon-lined autoclave and heated to 120 °C for 3 h to synthesize the nGO. After hydrothermal synthesis reaction, the nGO precipitates were washed with deionized water for several times and collected by centrifugation and then dried in vacuum. In step 3, 30 mg ammonium tetrathiomolybdate ((NH4)2MoS4) powder (ProChem, Inc., purity of 99.99 %) and 30 mg nGO powder were added to 4 mL N,N-dimethylformamide (DMF) for dispersion and then sonicated for 1 day. Subsequently, the dispersed solution was coated on fluorine-doped tin oxide (FTO) glass substrates (TEC-7, 2.2 mm, Hartford) by spin coating technology. Then, the obtained sample was dried in air for 1 h. Finally, the prepared sample was heated in the gas mixture (H2/Ar = 1:9) at 300 °C for 30 min by a typical homemade hot-wall thermal chemical vapor deposition (CVD) system (a horizontal furnace and a quartz tube) to obtain the 2D nanocomposite of MoS2/nGO CE.
Preparation of nGO, MoS2, and Pt CEs
For preparing the nGO CE, 30 mg of nGO powder was added to 3 mL of DMF dispersion and sonicated for 1 day. Subsequently, the nGO solution was spin-coated on FTO glass substrates and dried in vacuum at 120 °C for 30 min in our homemade hot-wall thermal CVD system. The MoS2 CE was prepared by using 4 wt% dispersed solution (0.8 g (NH4)2MoS4 powder in 20 mL DMF dispersion). The solution was coated on FTO glass substrates and dried in air for 1 h. Finally, the sample was heated in the gas mixture (H2/Ar = 1:9) at 300 °C for 30 min in the thermal CVD system to obtain MoS2 CE. For preparing the reference Pt CE, 2 mM H2PtCl6 isopropanol solution is coated on FTO glass substrates and heated to 450 °C for 20 min by thermal-reduced method .
Fabrication of DSSCs
For the preparation of the WE, nanocrystalline TiO2 was coated on FTO glass substrates by using screen print technology. The coated TiO2 samples were then heated to 550 °C for 30 min in the air. After the sinter process, the WE-coated TiO2 on FTO glass substrates was immersed into N719 (Solaronix) solution (0.3 mM in a mixture of acetonitrile and tertbutylalcohol (volume ratio 1:1)) at 50 °C for 1 h. Subsequently, the dye-adsorbed TiO2 WE was washed with acetonitrile for a few seconds to remove the remaining dye and dried at room temperature. Finally, the DSSCs were consisted of the WE, various CEs, and the iodide-based electrolyte (AN-50, Solaronix) with the 60-μm-thick hot-melt spacer (SX1170-60, Solaronix) between the two electrodes.
X-ray photoelectron spectroscopy (XPS) (PHI Quantera SXM/AES 650 Auger Electron Spectrometer (ULVAC-PHI INC., Japan) equipped with a hemispherical electron analyzer and a scanning monochromated Al K-α (hv = 1486.6 eV) X-ray source) was used to examine the chemical states of the prepared samples. Raman spectroscopy was performed with a confocal micro-Raman spectroscope (LABRAM HR 800 UV, Japan) using a 632.8-nm laser source (50 m W) with a spot size of approximately 1 μm to characterize the prepared CEs. The nanostructures of nGO nanosheet and MoS2/nGO nanocomposite were investigated by using the high-resolution transmission electron microscopy (HRTEM, JEOL-2100F, Japan). Cyclic voltammetry (CV) measurements were carried out by using a potentiostat/galvanostat (PGSTAT 302N, Autolab, Eco Chemie, Netherlands) in a three-electrode configuration to examine the electrocatalytic activities of our prepared CEs. The Pt wire and an Ag/AgNO3 electrode were used as the counter and reference electrodes for the CV measurements, respectively. The solution used for CV measurements contained 1 mM I2, 10 mM LiI, and 0.1 M LiClO4 in acetonitrile . Electrochemical impedance spectra (EIS) were obtained by using the aforementioned potentiostat/galvanostat equipped with a frequency response analysis (FRA) module. The Nyquist plots were scanned from 106 to 10−2 Hz, and an applied voltage of 10 mV was used. The EIS results were fitted by using an equivalent circuit model with Autolab FRA software (v4.9, EcoChemie B.V.). The Tafel polarization measurements were also measured by the same potentiostat/galvanostat equipped with a linear polarization module. Both EIS and the Tafel polarization measurements were obtained by using symmetrical devices based on two identical CEs in the dark. All photocurrent density–voltage measurements of DSSCs were measured under the simulated solar illumination (AM 1.5, 100 mW/cm2, Oriel 91160, Newport Corporation, USA), which was equipped with an AM 1.5G filter (Oriel 81088A, Newport Corporation, USA) and a 300-W xenon lamp (Oriel 6258, Newport Corporation, USA). The intensity of the simulated incident light was calibrated using a reference Si cell (calibrated at NREL, PVM-81).
Composition and Structural Features
N1s, Mo3d, and S2p peak positions and atomic percentages of MoS2/nGO
Fitting of the peak binding energy (eV) (atomic percentage (%))
Figure 1c shows the high-resolution Mo3d spectra of the MoS2/nGO nanocomposite, the 3d5/2 and 3d3/2 of the four valence states of Mo: Mo4+ 3d5/2 (229.3 eV) and Mo4+ 3d3/2 (232.4 eV); Mo5+ 3d5/2 (230.1 eV) and Mo5+ 3d3/2 (233.2 eV); Mo6+ 3d5/2 (231.3 eV) and Mo6+ 3d3/2 (234.4 eV); and Mo6+ 3d5/2 (232.5 eV) and Mo6+ 3d3/2 (235.6 eV), can be assigned to MoS2, Mo2S5, MoS3, and MoO3, respectively . Figure 1d shows that high-resolution S2p spectra of the MoS2/nGO nanocomposite, the 2p3/2 and 2p1/2, of the two valence states of S were assigned to MoS2 and Mo2S5, respectively. This phenomenon might correspond to the MoS3 with a formula of [Mo(4+)(S2)2−S2 −] and the intermediate product Mo2S5 . These binding energies can be attributed to the MoS2 crystal as previously reported [24, 36]. The summary of the peak positions (N1s, Mo3d, and S2p) and the atomic percentages were also given in Table 1.
C1s peak positions and atomic percentages of GO, nGO, and MoS2/nGO
Fitting of the C1s peak binding energy
(eV, atomic percentage (%))
Photovoltaic parameters and the electrochemical parameters from EIS, CV, and Tafel polarization measurements based on various CEs
I pc (mA/cm2)
E pp (V)
R s (Ω/cm2)
R ct (Ω/cm2)
N diff (Ω/cm2)
J 0 (mA/cm2)
J lim (mA/cm2)
V oc (V)
J sc (mA/cm2)
Photovoltaic Performance of DSSCs
The photocurrent–voltage characteristics of DSSCs with various CEs including Pt, nGO, MoS2, and MoS2/nGO were shown in Fig. 5d. The corresponding photovoltaic parameters were also summarized in Table 1. From the photovoltaic characteristics, the DSSCs with the nGO CE showed the lowest J sc (14.66 mA/cm2) and F.F. (0.38) and exhibited a lower PCE (3.95 %). The corresponding photovoltaic parameters of MoS2 CE showed that the PCE (4.09 %), J sc (15.39 mA/cm2), and F.F. (0.39) were higher than those of nGO CE. The results showed that the catalytic ability of MoS2 was higher than that of nGO. The J sc and F.F. values of the MoS2 CE were better than those of nGO CE, which might be due to the plenty edge sites of the MoS2. Compared with the nGO and MoS2, MoS2/nGO showed the excellent J sc (15.98 mA/cm2) and F.F. (0.53) and resulted in the outstanding PCE (5.95 %). In addition, all the CE materials exhibited the similar V oc values, because the DSSC devices in this study used the same WE and electrolyte. In summary, the 2D nanocomposite of MoS2/nGO combined the advantages of nGO and MoS2. The nGO provided a large surface area to anchor MoS2, and the plenty edge sites of the anchored MoS2 promoted the electrocatalytic activities. Furthermore, the promoted values of J sc and F.F. made the PCE (5.95 %) of MoS2/nGO nanocomposite CE comparable to the conventional Pt CE (6.43 %).
Based on the XPS, Raman spectrum, and HRTEM results, the sheet-like MoS2 was confirmed to form onto the surface of nGO nanosheet as the 2D nanocomposite of MoS2/nGO. According to CV, EIS, and the Tafel analyses, MoS2/nGO owned the outstanding electrocatalytic activities. The MoS2/nGO combined the advantages of the high specific surface of nGO and the plenty edge sites of MoS2 and showed the properties different from those of their individual constituents to create a new outstanding property. Finally, the DSSCs assembled with MoS2/nGO CE exhibited excellent photovoltaic conversion efficiency (5.95 %) which was comparable to the DSSC with the conventional Pt CE (6.43 %). This work demonstrated that the MoS2/nGO nanocomposite could offer a low-cost alternative to replace the expensive Pt in DSSCs.
This work was financially supported by the Ministry of Science and Technology of Taiwan (MOST 103-2221-E-131-029).
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- Oregan B, Gratzel M (1991) A low-cost, high-efficiency solar-cell based on dye-sensitized colloidal TiO2 films. Nature 353:737View ArticleGoogle Scholar
- Gratzel M (2003) Dye-sensitized solar cells. J Photochem Photobiol C-Photochem Rev 4:145View ArticleGoogle Scholar
- Gratzel M (2009) Recent advances in sensitized mesoscopic solar cells. Accounts Chem Res 42:1788View ArticleGoogle Scholar
- Shi ZW, Lu H, Liu Q, Cao FR, Guo J, Deng KM et al. (2014) Efficient p-type dye-sensitized solar cells with all-nano-electrodes: NiCo2S4 mesoporous nanosheet counter electrodes directly converted from NiCo2O4 photocathodes. Nanoscale Res Lett 9. DOI: 10.1186/1556-276X-9-608
- Nam JG, Park YJ, Kim BS, Lee JS (2010) Enhancement of the efficiency of dye-sensitized solar cell by utilizing carbon nanotube counter electrode. Scripta Mater 62:148View ArticleGoogle Scholar
- Huang SQ, Sun HC, Huang XM, Zhang QX, Li DM, Luo YH et al. (2012) Carbon nanotube counter electrode for high-efficient fibrous dye-sensitized solar cells. Nanoscale Res Lett 7. DOI: 10.1186/1556-276X-7-222
- Hsieh CK, Tsai MC, Yen MY, Su CY, Chen KF, Ma CCM et al (2012) Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells. Phys Chem Chem Phys 14:4058View ArticleGoogle Scholar
- Chen CS, Hsieh CK (2014) Oxygen-assisted low-pressure chemical vapor deposition for the low-temperature direct growth of graphitic nanofibers on fluorine-doped tin oxide glass as a counter electrode for dye-sensitized solar cell. Jpn J Appl Phys 53. DOI: 10.7567/JJAP.53.11RE02
- Ju MJ, Jeon IY, Lim K, Kim JC, Choi HJ, Choi IT et al (2014) Edge-carboxylated graphene nanoplatelets as oxygen-rich metal-free cathodes for organic dye-sensitized solar cells. Energ Environ Sci 7:1044View ArticleGoogle Scholar
- Wang H, Sun K, Tao F, Stacchiola DJ, Hu YH (2013) 3D honeycomb-like structured graphene and its high efficiency as a counter-electrode catalyst for dye-sensitized solar cells. Angew Chem Int Edit 52:9210View ArticleGoogle Scholar
- Kavan L, Yum JH, Gratzel M (2011) Optically transparent cathode for dye-sensitized solar cells based on graphene nanoplatelets. Acs Nano 5:165View ArticleGoogle Scholar
- Roy-Mayhew JD, Bozym DJ, Punckt C, Aksay IA (2010) Functionalized graphene as a catalytic counter electrode in dye-sensitized solar cells. Acs Nano 4:6203View ArticleGoogle Scholar
- Yen MY, Teng CC, Hsiao MC, Liu PI, Chuang WP, Ma CCM et al (2011) Platinum nanoparticles/graphene composite catalyst as a novel composite counter electrode for high performance dye-sensitized solar cells. J Mater Chem 21:12880View ArticleGoogle Scholar
- Sun LJ, Bai Y, Zhang NQ, Sun KN (2015) The facile preparation of a cobalt disulfide-reduced graphene oxide composite film as an efficient counter electrode for dye-sensitized solar cells. Chem Commun 51:1846View ArticleGoogle Scholar
- Wu ZS, Ren WC, Gao LB, Zhao JP, Chen ZP, Liu BL et al (2009) Synthesis of graphene sheets with high electrical conductivity and good thermal stability by hydrogen arc discharge exfoliation. Acs Nano 3:411View ArticleGoogle Scholar
- Long DH, Li W, Ling LC, Miyawaki J, Mochida I, Yoon SH (2010) Preparation of nitrogen-doped graphene sheets by a combined chemical and hydrothermal reduction of graphene oxide. Langmuir 26:16096View ArticleGoogle Scholar
- Deng SY, Jian GQ, Lei JP, Hu Z, Ju HX (2009) A glucose biosensor based on direct electrochemistry of glucose oxidase immobilized on nitrogen-doped carbon nanotubes. Biosens Bioelectron 25:373View ArticleGoogle Scholar
- Hou SC, Cai X, Wu HW, Yu X, Peng M, Yan K et al (2013) Nitrogen-doped graphene for dye-sensitized solar cells and the role of nitrogen states in triiodide reduction. Energ Environ Sci 6:3356View ArticleGoogle Scholar
- Jeong HM, Lee JW, Shin WH, Choi YJ, Shin HJ, Kang JK et al (2011) Nitrogen-doped graphene for high-performance ultracapacitors and the importance of nitrogen-doped sites at basal planes. Nano Lett 11:2472View ArticleGoogle Scholar
- Nolan H, Mendoza-Sanchez B, Kumar NA, McEvoy N, O'Brien S, Nicolosi V et al (2014) Nitrogen-doped reduced graphene oxide electrodes for electrochemical supercapacitors. Phys Chem Chem Phys 16:2280View ArticleGoogle Scholar
- Wang XR, Li XL, Zhang L, Yoon Y, Weber PK, Wang HL et al (2009) N-doping of graphene through electrothermal reactions with ammonia. Science 324:768View ArticleGoogle Scholar
- Lei B, Li GR, Gao XP (2014) Morphology dependence of molybdenum disulfide transparent counter electrode in dye-sensitized solar cells. J Mater Chem A 2:3919View ArticleGoogle Scholar
- Sie EJ, McIver J, Lee YH, Fu L, Kong J, Gedik N (2015) Valley-selective optical Stark effect in monolayer WS2. Nat Mater 14:290View ArticleGoogle Scholar
- Kibsgaard J, Chen ZB, Reinecke BN, Jaramillo TF (2012) Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis. Nat Mater 11:963View ArticleGoogle Scholar
- Radisavljevic B, Radenovic A, Brivio J, Giacometti V, Kis A (2011) Single-layer MoS2 transistors. Nat Nanotechnol 6:147View ArticleGoogle Scholar
- Zhan Y, Liu Z, Najmaei S, Ajayan PM, Lou J (2012) Large-area vapor-phase growth and characterization of MoS2 atomic layers on a SiO2 substrate. Small 8:966View ArticleGoogle Scholar
- Namgung SD, Yang S, Park K, Cho AJ, Kim H, Kwon JY (2015) Influence of post-annealing on the off current of MoS2 field-effect transistors. Nanoscale Res Lett 10:1View ArticleGoogle Scholar
- Castellanos-Gomez A, Poot M, Steele GA, van der Zant HSJ, Agrait N, Rubio-Bollinger G (2012) Mechanical properties of freely suspended semiconducting graphene-like layers based on MoS2. Nanoscale Res Lett 7:1View ArticleGoogle Scholar
- Xie J, Zhang H, Li S, Wang R, Sun X, Zhou M et al (2013) Defect-rich MoS2 ultrathin nanosheets with additional active edge sites for enhanced electrocatalytic hydrogen evolution. Adv Mater 25:5807View ArticleGoogle Scholar
- Marcano DC, Kosynkin DV, Berlin JM, Sinitskii A, Sun ZZ, Slesarev A et al (2010) Improved synthesis of graphene oxide. Acs Nano 4:4806View ArticleGoogle Scholar
- Papageorgiou N, Maier WF, Gratzel M (1997) An iodine/triiodide reduction electrocatalyst for aqueous and organic media. J Electrochem Soc 144:876View ArticleGoogle Scholar
- Mou ZG, Chen XY, Du YK, Wang XM, Yang P, Wang SD (2011) Forming mechanism of nitrogen doped graphene prepared by thermal solid-state reaction of graphite oxide and urea. Appl Surf Sci 258:1704View ArticleGoogle Scholar
- Khai TV, Na HG, Kwak DS, Kwon YJ, Ham H, Shim KB et al (2012) Influence of N-doping on the structural and photoluminescence properties of graphene oxide films. Carbon 50:3799View ArticleGoogle Scholar
- Lim J, Kim HA, Kim BH, Han CH, Jun Y (2014) Reversely fabricated dye-sensitized solar cells. Rsc Adv 4:243View ArticleGoogle Scholar
- Wang HW, Skeldon P, Thompson GE (1997) XPS studies of MoS2 formation from ammonium tetrathiomolybdate solutions. Surf Coat Tech 91:200View ArticleGoogle Scholar
- Liu CJ, Tai SY, Chou SW, Yu YC, Chang KD, Wang S et al (2012) Facile synthesis of MoS2/graphene nanocomposite with high catalytic activity toward triiodide reduction in dye-sensitized solar cells. J Mater Chem 22:21057View ArticleGoogle Scholar
- Brito JL, Ilija M, Hernandez P (1995) Thermal and reductive decomposition of ammonium thiomolybdates. Thermochim Acta 256:325View ArticleGoogle Scholar
- Mattevi C, Eda G, Agnoli S, Miller S, Mkhoyan KA, Celik O et al (2009) Evolution of electrical, chemical, and structural properties of transparent and conducting chemically derived graphene thin films. Adv Funct Mater 19:2577View ArticleGoogle Scholar
- Tang GG, Sun JR, Wei C, Wu KQ, Ji XR, Liu SS et al (2012) Synthesis and characterization of flowerlike MoS2 nanostructures through CTAB-assisted hydrothermal process. Mater Lett 86:9View ArticleGoogle Scholar
- Hou Y, Zhang B, Wen ZH, Cui SM, Guo XR, He Z et al (2014) A 3D hybrid of layered MoS2/nitrogen-doped graphene nanosheet aerogels: an effective catalyst for hydrogen evolution in microbial electrolysis cells. J Mater Chem A 2:13795View ArticleGoogle Scholar
- Mei XF, Meng XQ, Wu FM (2015) Hydrothermal method for the production of reduced graphene oxide. Physica E 68:81View ArticleGoogle Scholar
- Guo HL, Su P, Kang XF, Ning SK (2013) Synthesis and characterization of nitrogen-doped graphene hydrogels by hydrothermal route with urea as reducing-doping agents. J Mater Chem A 1:2248View ArticleGoogle Scholar
- Windom BC, Sawyer WG, Hahn DW (2011) A Raman spectroscopic study of MoS2 and MoO3: applications to tribological systems. Tribol Lett 42:301View ArticleGoogle Scholar
- Wu MX, Lin X, Wang YD, Wang L, Guo W, Qu DD et al (2012) Economical Pt-free catalysts for counter electrodes of dye-sensitized solar cells. J Am Chem Soc 134:3419View ArticleGoogle Scholar
- Kung CW, Chen HW, Lin CY, Huang KC, Vittal R, Ho KC (2012) CoS acicular nanorod arrays for the counter electrode of an efficient dye-sensitized solar cell. Acs Nano 6:7016View ArticleGoogle Scholar
- Wei YH, Chen CS, Ma CCM, Tsai CH, Hsieh CK (2014) Electrochemical pulsed deposition of platinum nanoparticles on indium tin oxide/polyethylene terephthalate as a flexible counter electrode for dye-sensitized solar cells. Thin Solid Films 570:277View ArticleGoogle Scholar