Synthesis and Performance of La2Mo2O7 with MWCNTs Composite Materials as Pt-Free Counter Electrodes for Dye Sensitized Solar Cells

Ke-Zhong WU Jia-Jing ZHAO Yuan-Yuan XIONG Bei RUAN Ming-Xing WU

Citation:  WU Ke-Zhong, ZHAO Jia-Jing, XIONG Yuan-Yuan, RUAN Bei, WU Ming-Xing. Synthesis and Performance of La2Mo2O7 with MWCNTs Composite Materials as Pt-Free Counter Electrodes for Dye Sensitized Solar Cells[J]. Chinese Journal of Inorganic Chemistry, 2018, 34(11): 2041-2048. doi: 10.11862/CJIC.2018.249 shu

染料敏化太阳能电池对电极La2Mo2O7复合MWCNTs非Pt催化剂的制备与性能

    通讯作者: 武明星, sc05019017@163.com
  • 基金项目:

    国家自然科学基金 21303039

    国家自然科学基金 21473048

    国家自然科学基金(No.21473048, 21303039), 河北自然科学基金(No.B2015205163, B2016205161), 河北省科技厅计划项目(No.16211117)和河北教育厅计划项目(No.QN2017087)资助

    河北教育厅计划项目 QN2017087

    河北自然科学基金 B2016205161

    河北省科技厅计划项目 16211117

    河北自然科学基金 B2015205163

摘要: 通过高温固相法对醋酸镧(C6H9O6La·xH2O)与高钼酸铵((NH4)6Mo7O24·4H2O)在一定条件下热解制备非Pt催化剂La2Mo2O7(La2O3-2MoO2)。进一步采用2种方法将La2Mo2O7与多壁碳纳米管(MWCNTs)进行复合, 一种是将La2Mo2O7喷涂到MWCNTs表层之上得到La2Mo2O7/MWCNTs, 另一种是将两者均匀混合掺杂得到La2Mo2O7@MWCNTs, 再将上述2种复合材料应用于染料敏化太阳能电池对电极进行相应研究。通过扫描电子显微镜(SEM)表征了复合催化材料的微观形貌, X射线衍射(XRD)确定了微观结构。采用电流密度-光电压曲线、循环伏安, 交流阻抗以及塔菲尔极化分析了材料的光电性能。实验结果表明在电解液I3-/I-中, 基于La2Mo2O7/MWCNTs与La2Mo2O7@MWCNTs的对电极, 相同的条件下在光电池中获得的光电转换效率分别为6.09%和4.84%, 明显高于MWCNTs的3.94%和La2Mo2O7的0.87%。电极性能的提高可归因于La2Mo2O7复合催化剂相对大的比表面积和高导电性。

English

  • Dye sensitized solar cells (DSSCs) directly convert solar energy into electricity to improve energy effici-ency and protect the environment[1-3].DSSCs consist of a transparent photoanode, electrolyte, and a counter electrode (CE).The CE is an important component of DSSCs and plays an important role in collecting electrons from an external circuit and in catalyzing the regeneration of the redox couple at the CE/electrolyte interface[4-5].Generally, Pt is widely used as a catalytic material on CEs because of its high catalytic activity and high efficiency[6-8].However, Pt is not only expensive and rare but can also be readily corroded by the I3-/I- electrolyte.Development of Pt-free catalysts is considered to be one of the crucial steps toward improved energy conversion efficiency and low-cost alternatives of DSSCs.

    A significant amount of Pt-free catalytic materials for the CE in DSSCs has been reported, and these materials have included carbon materials (activated carbon, multiwall carbon nanotubes (MWCNTs), graphite, nanotubes, graphene, and C60)[9-12], conducting and doped polymers (polypyrrole (PPy), polyaniline (PAn), polythiophene (PTh), polyphenylene (PPP), and poly-(3, 4-ethylene dioxythiophene) (PEDOT))[13-15], and transition metal compounds (oxides, nitrides, carbides, sulfides, and selenides)[16-25].Among the transition metal compounds, La-Mo compounds and their corresponding composites might be essential in various electro-chemical devices because of their great flexibility in structure and morphology, convenience in synthesis, and high electrocatalytic activity toward the electr-olyte[26]. Wu et al.[27] synthesized molybdenum carbide microspheres (Mo2C-Ms) and nanorods (Mo2C-Nr) as CE catalysts.The DSSCs resulted in power conversion efficiencies (PCEs) of 5.50% and 4.86% for Mo2C-Ms and Mo2C-Nr, respectively.The performance of single catalysts can be further improved through the use of conductive carbon and carbon derivative materials.Previously, Jin et al.[28] successfully synthesized nano-composites of the perovskite-phase La0.65Sr0.35MnO3 with reduced graphene oxide (LSMO@RGO).Areerob et al.[29] fabricated DSSCs using La/TiO2-graphene nanocomposite CEs and their DSSCs yielded a PCE of 6.75%. La/TiO2-graphene CEs exhibited efficient electrocatalytic ability because the catalytic La particles were uniformly distributed on the surface of graphene.

    In our preliminary experiments, we have synthesized a series of solid solution and intermediate compounds of La2O3-MoO3, with the different stoichio-metric ratios from 0:1 to 1:0, according to the phase diagram of La2O3-MoO3[30].The performance of La2Mo2O7 as a CE catalyst is superior to other materials for the reduction of I3-/I- in DSSCs.Herein, we combined La2Mo2O7 with MWCNTs to synthesize La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs electrodes to improve the performance of DSSCs.Carbon composites have attracted research attention for enhancing the value of products and for reducing production costs, which has become increasingly important.MWCNTs is a kind of carbon material that has a significant amount of void spaces, a large specific surface area, and acts as a carrier and catalyst[31].La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs were investigated in iodine electrolyte, and they exhibited high PCEs in DSSCs.The composites have both the increased active surface area of the MWCNTs and the coupling effects between La2Mo2O7 and MWCNTs[19].La2Mo2O7/MWCNTs comp-osite catalytic materials exhibited high electrocatalytic activity and low charge transfer resistance.

    Lanthanum acetate hydrate (La(CH3COO)3·xH2O, 99.9%, molecular weight:316.04) was supplied by Aladdin, Shanghai.Hexaammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24·4H2O, ≥99.0%, molecular weight:1 235.86) was supplied by Sinopharm Chemical Reagent Co., Ltd.MWCNTs was supplied by Aladdin, Shanghai.All reagents and solvents were analytical grade and were used without further purification.La(CH3COO)3·xH2O and ((NH4)6Mo7O24·4H2O) were mixed according to their stoichiometric ratio and ground in an agate mortar with 3 mL of ethanol.The mixture was then placed in an oven to dry at 150 ℃ and pressed at 8 MPa into pellets that had a 10 mm diameter.Then, La2Mo2O7 (La2O3-2MoO2) was obtained from the solid precursor via a high-temperature solid phase reaction at 800 ℃ for 8 h in air.The synthesis of La2Mo2O7@MWCNTs was performed by doping 0.125 0 g of La2Mo2O7 on 0.025 0 g of MWCNTS in isopropanol solvent using ultrasonic dispersion for 15 min.The mixture pastes of La2Mo2O7@MWCNTs were obtained for La2Mo2O7 and MWCNTs with mass ratios of 5:1.

    Pt, pure La2Mo2O7, La2Mo2O7@MWCNTs and La2Mo2O7/MWCNTs composites were used as CEs and prepared as follows:An FTO glass substrate piece was cleaned with distilled water, then cleaned with a mixture of ethanol and acetone in an ultrasonic bath, and dried under a hot dryer.Then, 100 mg of the prepared La2Mo2O7, La2Mo2O7@MWCNTs and the purchased MWCNTs were respectively dispersed in 2 mL of isopropanol.These mixture pastes were obtained via ball-milling for 50 min and directly sprayed on each FTO glass using an airbrush.The thickness of the electrode was about (12±1) μm.The preparation of La2Mo2O7/MWCNTs was first sprayed with 6 μm of MWCNTs on the FTO glass and then sprayed with 6 μm of La2Mo2O7 onto the surface of the MWCNTs.La2Mo2O7 and MWCNTs show upper and lower layers on the FTO glass.Followed by next step, the FTO glass, which was coated with active material paste of La2Mo2O7, La2Mo2O7@MWCNTs, MWCNTs and La2Mo2O7/MWCNTs, was sintered at 500 ℃ under N2 flow for 30 min, and the CEs were obtained.Preparation of the Pt CE was carried out using a chemical reduction method.A mass fraction of 5% chloroplatinic acid isopropanol was sprayed onto the ITO substrate and dried at 120 ℃ for 1 h.Then, the ITO substrate was rapidly immersed in an aqueous solution of 30 mmol·L-1 NaBH4 for 3 min.The ITO substrate was then removed and rinsed with water and absolute ethanol and dried at 120 ℃ for 1 h.The photoanode used in the DSSCs was a 12-mm thick TiO2 film sensitized with N719 dye.The electrolyte I3-/I- contained 0.1 mol·L-1 LiI, 0.6 mol·L-1 1-propyl-3-methylimidazolium iodide, 0.07 mol·L-1 I2, 0.5 mol·L-1 4-tert-butyl pyridine, and 0.1 mol·L-1 guanidinium thiocyanate in 3-methoxypropionitrile (MPN).The active area of the electrode was about 0.4 cm×0.4 cm.For electrochemical measurements, the symmetrical cell had a sandwich configuration and was fabricated with two identical CEs clipping the electrolyte together using hot-melt surlyn film.

    The XRD pattern of La2Mo2O7, MWCNTs and La2Mo2O7@MWCNTs material powders was taken by a D8 Bruker X-ray diffractometer (λ=0.154 nm) using Cu radiation (Ni filter) at 2°·min-1 with 2θ ranging from 10° to 70°.The voltage is 40 kV and the current is 40 mA.Scanning electron microscopy (SEM) was performed with an S-4800 SEM instrument (Hitachi, Japan) at an accelera-tion voltage of 3 kV.The cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization tests were performed using a CHI 660E (SHANGHAI, CHEN HUA) electrochemical analyzer.The CV experiments were carried out in a two-compartment glass cell with a three-electrode configuration at 25 ℃ in an acetonitrile solution containing 1 mmol·L-1 iodine (I2), 0.1 mol·L-1 LiClO4 (lithium perchlorate), and 10 mmol·L-1 LiI (lithium iodate).The as-fabricated CEs acted as the working electrode, the Pt sheet (4 cm2) as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode.All potentials were presented on the SCE scale.EIS was carried out in the frequency range of 0.01~105 Hz at 0 V bias voltage with perturbation amplitude of 5 mV in the dark.Tafel polarization was measured at a scan rate of 10 mV·s-1 from -0.7 to 0.7 V.The assembled DSSCs were illuminated under AM 1.5 illumination (I=100 mW·cm-2, PEC-L01, Peccell, Yokohama, Japan) with a digital source meter (Keithley 2601, Cleveland, OH).

    The XRD patterns for MWCNTs, La2Mo2O7, and La2Mo2O7@MWCNTs were recorded at room tempera-ture and are presented in Fig. 1.In the diffraction pattern of the powder sample, the most intense diffra-ction peak values of La2Mo2O7 are at 15.96°, 27.65°, 28.14°, 31.06°, 33.50°, 39.83°, 46.49°, 48.76°, 52.90°, 55.66°, and 64.35°, which could be well identified as (210), (310), (011), (111), (120), (301), (002), (610), (421), (430), and (422) and matched well with pristine La2Mo2O7 (PDF No.84-1234).Fig. 1 shows a typical XRD pattern of MWCNTs subjected to N2 annealing at 500 ℃.It is known that MWCNTs have a strong and sharp characteristic peak at 2θ=26.59°, and this peak is attributed to diffraction of the single carbon atom.The diffraction patterns of La2Mo2O7@ MWCNTs are similar to that of pure La2Mo2O7.The amorphous peak of MWCNTs is relatively weak in the La2Mo2O7@MWCNTs sample, and this result indicates that MWCNTs was barely physically combined with La2Mo2O7 as catalyst carriers.

    Figure 1

    Figure 1.  XRD patterns of the prepared MWCNTs, La2Mo2O7 and La2Mo2O7@MWCNTs

    Fig. 2 shows the morphologies of the MWCNTs, La2Mo2O7, La2Mo2O7@MWCNTs, and La2Mo2O7/MWCNTs.The MWCNTs had attained a clear shape of nanofibers with smooth, uniform and beads-free surface (Fig. 2(a)).There are some void spaces, observed around the MWCNTs.The particle size of La2Mo2O7 is the smallest and more evenly distributed, as seen in Fig. 2(b). Fig. 2(c) shows that La2Mo2O7 was fully combined with MWCNTs to construct La2Mo2O7@ MWCNTs; Fig. 2(d) shows sectional view morphology that the small area La2Mo2O7 coating was scraped away from the surface of the La2Mo2O7/MWCNTs electrode using a blade.The La2Mo2O7/MWCNTs electrode presents upper and lower layers.The intact part of the electrode La2Mo2O7 is uniformly distributed over the MWCNTs.

    Figure 2

    Figure 2.  SEM images of the prepared MWCNTs (a), La2Mo2O7 (b), La2Mo2O7@MWCNTs (c) and La2Mo2O7/MWCNTs (d)

    Fig. 3 presents photocurrent density-voltage (J-V) curves of the DSSCs using CEs based on Pt, MWCNTs, La2Mo2O7, La2Mo2O7/MWCNTs, and La2Mo2O7@ MWCNTs.The photovoltaic parameters are presented in Table 1, where Voc presents the open-circuit voltage.Fig. 3 shows that PCEs of 6.09% and 4.84% were obtained for La2Mo2O7/MWCNTs and La2Mo2O7@ MWCNTs, respectively, and these values were superior to the PCEs of Pt (4.54%), MWCNTs (3.94%), and La2Mo2O7 (0.87%) CE-based DSSCs.The short-circuit current density (JSC) of the four materials were in the order of: La2Mo2O7/MWCNTs (12.19 mA·cm-2) >La2Mo2O7@MWCNTs (10.88 mA·cm-2) > MWCNTs (9.75 mA·cm-2) > La2Mo2O7 (8.88 mA·cm-2).The significantly enhanced JSC values contribute to the improved performance of the DSSCs and reveal that the rate of pore recovery at the La2Mo2O7@MWCNTs and La2Mo2O7/MWCNTs electrode-electrolyte interface were faster than that at the electrode-electrolyte interface of the other CEs.Furthermore, fill factor (FF) values of the La2Mo2O7/MWCNTs and La2Mo2O7@ MWCNTs cathodes were as high as 0.64 and 0.63, which were higher than the FF of 0.13 indicated by the La2Mo2O7 CE-based DSSC.FF mainly reflects the internal resistance of the electrode/electrolyte in a cell.Thus, the higher JSC and FF values for the four materials used as CEs are ascribed to the consid-erable enhancement in charge transfer at the CE/electrolyte interface and to catalytic ability, which lowers the internal resistances, the concentration gradients in the electrolyte, and the recombination rates[32]. The high catalytic activity of each of the La2Mo2O7@MWCNTs and La2Mo2O7/MWCNTs used in the DSSCs could be because of the MWCNTs increased catalytic surface area of the electrode films.

    Figure 3

    Figure 3.  J-V characteristics of DSSCs with different samples as CEs under a light intensity of 100 mW·cm-2

    Table 1

    Table 1.  Photovoltaic parameters for the DSSCs assembled with various CEs
    下载: 导出CSV
    CE Voc / mV JSC / (mA·cm-2) FF PCE / %
    Pt 779 11.63 0.50 4.54
    MWCNTs 643 9.75 0.63 3.94
    La2Mo2O7 777 8.88 0.13 0.87
    La2Mo2O7@MWCNTs 710 10.88 0.63 4.84
    La2Mo2O7/MWCNTs 786 12.19 0.64 6.09

    The CV measurements were conducted at a scan rate of 20 mV·s-1 to determine the electrocatalytic kinetics of five materials toward the reduction couple of I3-/I- in 3-methoxypropionitrile solution, which consisted of 1 mmol·L-1 I2, 10 mmol·L-1 LiI and 0.1 mol·L-1 LiClO4.The CV curves are presented in Fig. 4.It is noteworthy that two oxidation-reduction couples were observed in the CV curves of all five samples.

    Figure 4

    Figure 4.  CV curves of various CE electrodes for the I-/I3- electrolyte

    The reduction peaks in the negative potential could be associated with the reaction:I3-+2e- → 3I-; the oxidation peaks in the negative potential correspond to the reaction:3I- → I3-+2e- [33].Two main parameters from the CV curve demonstrated the entire electrocatalytic abilities, and these parameters were the peak-to-peak separation (ΔEp) and the cathodic peak current density (IP) at more negative potential.In the case of composites, the ΔEp values of La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs were 0.222 and 0.237 V, respectively.The values of ΔEp are lower than that of the CE assembled with the La2Mo2O7 (0.377 V) electrode, and this indicates the enhanced electrocatalytic activity and reversibility of the La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs CEs.The ΔEp value is attributed to the redox ability of the counter electrode to electric pair in electrolytes.The lower ΔEp value corresponds to the higher redox capability of CE for I3-/I-.The IP values from the CV profile also demonstrated the electrocatalytic activity of CE.The IP values of the La2Mo2O7/MWCNTs (1.255 mA·cm-2) and La2Mo2O7@MWCNTs (0.702 3 mA·cm-2) composite CEs are higher than that of the CEs with the La2Mo2O7 (0.211 0 mA·cm-2), MWCNTS (0.412 0 mA·cm-2), and Pt (0.363 0 mA·cm-2) electrodes.The higher IP values indicated the excellent electrocatal-ytic activity of the two La2Mo2O7-MWCNTs compo-sites, which are promising as Pt-free efficient CEs in DSSCs.Moreover, the catalytic reaction is a kinetic process, which is associated with the electron transfer rate constant and the number of active sites.The ntegral area of the negative redox peak for each of the two composite electrodes was bigger than that for La2Mo2O7 (La2O3-2MoO2) and MWCNTs, which indicateed that the La2Mo2O7-MWCNTs composite structure provides more catalytic reaction sites than the La2Mo2O7 and MWCNTs CEs.

    EIS was carried out to assess the electrical conductivity and electrochemical catalytic activities of the CEs.Fig. 5 presents the Nyquist plots of the symmetric cells using different materials as the CEs.The charge transfer resistance (Rct) of the CE can be taken as half the value of the real semicircles in the high-frequency region.The Rct values of Pt, MWCNTs, La2Mo2O7, and the La2Mo2O7@MWCNTs and La2Mo2O7/MWCNTs composites were 54.0, 634.4, 2 007.3, 328.4, and 262.2 Ω, respectively.The data indicate that the Rct value of the La2Mo2O7 electrode is much larger and the La2Mo2O7/MWCNTs composite electrode is smaller than those of the other CE-based cells.The La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs CEs demonstrated better redox capacity and high electrocatalytic ability than the La2Mo2O7 and MWCNTs CE.This is attributed to the lower conductivity of the composites and the accelerated high electron transmission at the CE/electrolyte interface, which thus result in higher Jsc and FF.

    Figure 5

    Figure 5.  Nyquist plots for symmetrical cells based on various CEs

    Tafel polarization curves were recorded at a scan rate of 10 mV·s-1 from -0.7 to 0.7 V to estimate the electrocatalytic activity of different CEs for I3- reduction.The exchange current density (J0) of DSSCs can be regarded as the intercept of the extrapolated linear region of the anodic and cathodic branches when the potential is zero.The anodic and cathodic branches of the Tafel curves for La2Mo2O7/MWCNTs and the composite La2Mo2O7@MWCNTs CEs show larger slopes than that for the MWCNTs and La2Mo2O7 CEs, exhibiting a higher exchange current density (J0) on CE in Fig. 6[30]. Both the La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs CEs demonstrated higher J0 values than the La2Mo2O7 and MWCNTs electrodes, and a maximal J0 value for the La2Mo2O7/MWCNTs CE was observed.Obviously, the order of J0 is La2Mo2O7/MWCNTs (0.416 4 mA·cm-2) > La2Mo2O7@MWCNTs (0.199 1 mA·cm-2) > MWCNTs (0.158 6 mA·cm-2) >La2Mo2O7 (0.019 96 mA·cm-2). This order indicates that the La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs composites possessed higher diffusion velocities and better electrocatalytic activities for the reduction of I3- than the MWCNTs and La2Mo2O7 CEs.This is consistent with the trend of the cathodic peak current shown in the CV curve.The J0 value can be directly calculated using Eq.(1):

    $ {J_0} = \frac{{RT}}{{nF{R_{{\rm{ct}}}}}} $

    (1)

    Figure 6

    Figure 6.  Tafel plots of symmetrical cells between -0.7~0.7 V with a scan rate of 10 mV·s-1 at room temperature

    Where R is the gas constant, T is the absolute temperature (K), n is the number of electrons related to the electrochemical reduction reaction in the reduction of I3-.The J0 value is inversely proportional to the Rct value.A larger J0 value indicates more electrons migrating through the CE/electrolyte interface, and this thereby indicates that the catalytic film has a faster electron transfer capability.Tafel polarization results match well with EIS and CV results.The experimental results clearly reveal that the composite of La2Mo2O7 and MWCNTs obtained the higher charge transfer between I3- ions and the La2Mo2O7/MWCNTs surfaces and the rapid redox transfer reaction of I3-/I- in a dye-sensitized solar cell system.

    The La2Mo2O7/MWCNTs CEs demonstrated higher PCE, Jsc and Voc of CEs values than that of Pt, La2Mo2O7, La2Mo2O7@MWCNTs and MWCNTs CEs from J-V curves.The maximal PCE value was obtained for La2Mo2O7/MWCNTs composite, which was 6.09%.The CV results were in good agreement with the PCE results from J-V measurements.From the CV curves, La2Mo2O7/MWCNTs had shown the lowest ΔEp and highest IP.The Tafel polarization results indicated that La2Mo2O7/MWCNTs CEs obtained the higher J0, as compared to other CEs, which indicated a higher catalytic activity of composite CEs.According to Eq.(1), the Rct was inversely proportional to J0.We can deduce that Rct of composite CEs was higher than that of La2Mo2O7 and MWCNTs, which is in good agreement with the experimentally measured Rct from EIS.Compared with La2Mo2O7@MWCNTs, La2Mo2O7/MWCNTs enhanced catalytic active sites, increased exchange current density and load resistance reduction at CE/electrolyte interface.

    The CV, EIS, Tafel, and J-V characterizations demonstrated that the La2Mo2O7/MWCNTs CEs could catalyze the regeneration of the I3-/I- couple, as effec-tively as Pt.In addition, a desirable catalyst should possess robust stability along with high catalytic activity.Thus, herein, we checked the electrochemical stability of the La2Mo2O7/MWCNTs CEs via conse-cutive CV cycling (Fig. 7).After 10 consecutive CV cycles, minor current density attenuation or no peak position shift was observed, this demonstrates that La2Mo2O7/MWCNTs was stable and coexist with the I3-/I- redox couples.

    Figure 7

    Figure 7.  CVs of La2Mo2O7/MWCNTs CE for the I-/I3- electrolyte 1st and 10th cycle

    Composite materials of La2Mo2O7 with MWCNTs were successfully synthesized using a high-temper-ature solid-state reaction.La2Mo2O7 was modified on the surface of MWCNTs to synthesize La2Mo2O7/MWCNTs and doped in MWCNTs to synthesized La2Mo2O7@MWCNTs.Both composite materials served as Pt-free catalytic materials for CEs for efficient DSSCs.MWCNTs and La2Mo2O7 combined to expand the surface area, increase the exchange current density of the composite materials, and reduce the load resistance at the counter electrode/electrolyte interface.MWCNTs act as both a carrier and a catalyst.Power conversion efficiency values of 6.09% and 4.84% were obtained for La2Mo2O7/MWCNTs and La2Mo2O7@MWCNTs, respectively, using each as a counter electrode, and these values are superior to those of Pt (4.54%), La2Mo2O7 (0.87%), and MWCNTs (3.94%) toward the reduction of I3-/I- ions.Thus, after an integrated analysis of the CV, EIS, and Tafel polarization results, we conclude that the La2Mo2O7/MWCNTs hybrids are potential catalysts for replacing Pt for future large-scale fabrication of DSSCs.

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  • Figure 1  XRD patterns of the prepared MWCNTs, La2Mo2O7 and La2Mo2O7@MWCNTs

    Figure 2  SEM images of the prepared MWCNTs (a), La2Mo2O7 (b), La2Mo2O7@MWCNTs (c) and La2Mo2O7/MWCNTs (d)

    Figure 3  J-V characteristics of DSSCs with different samples as CEs under a light intensity of 100 mW·cm-2

    Figure 4  CV curves of various CE electrodes for the I-/I3- electrolyte

    Figure 5  Nyquist plots for symmetrical cells based on various CEs

    Figure 6  Tafel plots of symmetrical cells between -0.7~0.7 V with a scan rate of 10 mV·s-1 at room temperature

    Figure 7  CVs of La2Mo2O7/MWCNTs CE for the I-/I3- electrolyte 1st and 10th cycle

    Table 1.  Photovoltaic parameters for the DSSCs assembled with various CEs

    CE Voc / mV JSC / (mA·cm-2) FF PCE / %
    Pt 779 11.63 0.50 4.54
    MWCNTs 643 9.75 0.63 3.94
    La2Mo2O7 777 8.88 0.13 0.87
    La2Mo2O7@MWCNTs 710 10.88 0.63 4.84
    La2Mo2O7/MWCNTs 786 12.19 0.64 6.09
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  • 发布日期:  2018-11-10
  • 收稿日期:  2018-03-21
  • 修回日期:  2018-09-01
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