English

• 0.   Introduction

  As global energy demand continues to grow annually, the advancement of renewable energy becomesincreasingly vital^[1-3]. Among all renewable energy technologies, photovoltaic technology stands out as the most promising^[4-9]. The third-generation dye-sensitized solar cells (DSSCs) are widely employed due to their cost-effectiveness, straightforward fabrication, stable performance, and high PCE^[10-14]. Typical DSSCs feature a sandwich structure, consisting primarily of a counter electrode (CE), a sensitizing dye, a photoanode, and an electrolyte^{[8, 15-17]}. Pt, owing to its superior conductivity and catalytic activity in triiodide reduction, remains the most frequently used CE material in traditional iodine electrolytes for DSSCs^[18-21]. However, Pt cannot be widely used due to its material scarcity and high price^[22-23]. Therefore, identifying CE materials with superior electrochemical stability and enhanced economic efficiency to replace Pt is essential for the rapid advancement of DSSCs.

  Transition metal sulfides (TMSs) are widely used because of their excellent physical and chemical properties. Their amorphous state has more defects and active sites, and their nanomaterials have characteristics of short-range order and long-range disorder, which can be used to prepare battery electrode materials and catalysts related to the chemical industry. The inherent disordered structure of amorphous materials will enhance their activity, resulting in the increase of active sites and the improvement of the intrinsic activity of these sites, showing better activity than crystal nanomaterials in fields such as hydroelectrolysis. Due to its excellent catalytic performance, it is widely used in hydrogen evolution, water decomposition, and supercapacitors^[24-25]. The amorphous phase increases the catalytic activity of electrolyte regeneration due to lattice distortion and more marginal overhanging bonds. Yu et al. prepared an amorphous nitrogen-doped carbon MoS₃ nanobattery with a hollow porous structure, which could achieve high capacity and improve battery life for Li-S batteries^[26]. Jiang et al. used a gas/liquid/solid interface self-assembly method to prepare ordered two-dimensional amorphous Co-S nanoarrays on clean F-doped tin oxide conductive glass (FTO) glass, and the PCE of DSSCs composed of this CE was 7.78%, about 20% higher than that of a traditional Pt CE (6.51%)^[27].

  Transition metal Ni has good catalytic activity, so its introduction can effectively enhance catalytic activity. For example, Jiang′s group directly generated amorphous Ni-CO-S films in FTO by electrodeposition technology, and used them as DSSC CEs with a PCE of 8.18%, which was much higher than the rare metal Pt CE^[28]. Similarly, the Fe element also has a similar activity to Ni. The catalytic capacity of hydrogen evolution when ternary transition metal sulfide was used as a catalyst, was comparable to that of Pt. Amorphous FeMoS₄ has stronger activity when used for electrocatalytic hydrogen evolution^[29-30]. Therefore, introducing FeMoS₄ into DSSCs as a CE catalytic material may increase PCE. However, as TMSs also have similar defects, the conductivity is not good, so an appropriate substrate should be selected. Carbon fiber cloth (CC) is composed of carbon fiber with a diameter of 5-10 μm, which has excellent electrical conductivity. To further modify the surface of CC, nanostructures can be grown on the surface of CC to increase the active sites required for electrochemical reaction. FeMoS₄ is widely used in various catalytic fields such as electrocatalytic hydrogen evolution, wastewater treatment, supercapacitors (symmetric and asymmetric), and lithium batteries, and is an excellent carrier for composite materials^[31].

  Therefore, the combination of CC and TMSs can better coordinate the advantages of both. Herein, a simple two-step hydrothermal method was adopted to synthesize an amorphous FeMoS₄/CC (FMS/CC) composite. A series of characterizations confirmed the successful preparation of amorphous FMS/CC. The amorphous substances can supply more active sites and accelerate the decrease of I₃^-. Moreover, by scraping and coating on a flexible titanium mesh, which possesses lower sheet resistance, the resulting DSSCs exhibited a lower series resistance (R_s) compared to those fabricated on conventional FTO conductive substrates under identical conditions. At the same time, electrochemical methods such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the PCE of DSSCs using FMS/CC as CE was about 9.51%, which was higher than that of the Pt CE (about 8.15%), indicating that the use of amorphous transition metal sulfide instead of non-platinum materials has great potential.

  1.   Experimental

  1.1   Materials

  Chemical reagents such as FeCl₃·6H₂O, urea, (NH₄)₂MoS₄, polyacrylonitrile (PAN), nano TiO₂ (P25), N, N-dimethylformamide (DMF) were purchased from McLean Reagent Co., Ltd., and directly used without any treatment. FTO (15 Ω·cm²) was purchased from NSG Company in Japan.

  Scheme 1

  

  Scheme 1.  Fabrication process of the DSSC CE with the FMS/CC composite

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  1.2   Preparation of FMS/CC

  In a typical synthesis, the FeOOH/CC precursor was first prepared. FeCl₃·6H₂O (8.5 mmol) and urea (20 mmol) were dissolved in 35 mL of deionized water and stirred for 30 min to form a transparent, light orange solution. Before use, the CC was soaked in hydrochloric acid for 30 min and then rinsed three times with deionized water. A piece of clean CC (0.2 g) was then added, and the mixture was sealed in a 50 mLautoclave and heated at 100 ℃ for 4.5 h. After cooling to room temperature, the product was washed repeatedly and dried at 55 ℃ to obtain the FeOOH/CC precursor. Subsequently, the precursor was vulcanized to synthesize the final product. The as-prepared FeOOH/CC was immersed in a solution containing (NH₄)₂MoS₄ (0.15 mmol) dissolved in 30 mL of deionized water. This mixture was subjected to a second hydrothermal treatment in an autoclave at 160 ℃ for 11 h. Finally, after cooling to ambient temperature, the resulting sample was collected, washed thoroughly, and dried, yielding the lamellar FMS/CC composite. For comparison, a control sample of pure FMS powder was synthesized following the identical procedure, except that CC was omitted from the hydrothermal solution; all subsequent steps, including annealing, remained the same.

  1.3   Preparation of the CE

  0.15 g of FMS/CC was cut into pieces and ground into powder in the mortar. After undergoing two rounds of hydrothermal treatment, the CC exhibited a certain degree of brittleness. Subsequently, it was cut into pieces and subjected to high-energy ball milling, enabling it to be ground into powder and achieve uniformity. Then, the scraping paste (A paste was formulated by blending ethyl cellulose, terpineol, and ethanol with a mass ratio of 1:4:10) was added, and continued grinding. After about 20 min, when the material in the mortar became a paste, it was scraped onto the clean titanium mesh fixed on the scraping table with a special scraper blade. The scraping area was 0.7 cm×5 cm, and the scraping process strength was uniform to avoid uneven CE film thickness. The scraped CE was dried at 90 ℃ for 4 h, then placed in a tube furnace filled with nitrogen and heated at 500 ℃ for 4 h, and the CE was obtained after the temperature dropped. During the experiment, control variables were used: only the film thickness of the CE was changed, and other conditions remained unchanged. The preparation method of the CEs with different film thicknesses was the same as above, and the film thickness of the CE was changed by changing the number of transparent tape layers. For convenience of recording, the CEs with thicknesses of 9, 11, 13, 15, and 17 µm were abbreviated as FMS/CC-x, where x was 1, 2, 3, 4, and 5, respectively.

  1.4   Fabrication of DSSCs

  The TiO₂ photoanode was prepared on a clean 0.36 cm² FTO via silkscreen five times to control the film thickness at about 15 μm. Thereafter, the TiO₂ photoanode was stabilized at 500 ℃ for 30 min under an air atmosphere. To further use, the TiO₂ photoanode was immersed in N719 dye solution for 24 h to obtain the dye-sensitized TiO₂ photoanode. The electrolyte was prepared by dissolving lithium iodide (LiI, 0.06 mol·L^-1), iodine (I₂, 0.03 mol·L^-1), 4-tert-butylpyridine (TBP, 0.5 mol·L^-1), 1-propyl-3-methylimidazolium iodide (PMII, 0.6 mol·L^-1), and guanidinium thiocyanate (GSCN, 0.1 mol·L^-1) in acetonitrile. The resulting solution was then magnetically stirred for 30 min toensure homogeneity. At last, the prepared titanium mesh was pasted on the glass and assembled with the TiO₂ photoanode, sealed with a thin film.

  Many factors affect the electrocatalytic activity of DSSCs on CEs. To explore the effect of film thickness on the electrocatalytic performance of CEs, five sets of FMS/CC CEs with different film thicknesses and a comparison experiment with Pt CEs were designed, and a series of electrochemical characterizations were conducted on them.

  1.5   Measurement

  The surface morphology and lattice structure of FMS/CC were investigated by field emission scanning electron microscopy (SEM, FEI, NOVA NanoSEM 450) and transmission electron microscopy (TEM, 200 kV, JEOL, JEM-2100 Plus). The phase structure of the sample was analyzed by X-ray diffraction (XRD, D8-Advance, Bruker AXS, Cu Kα radiation, λ=0.154 06 nm, 40 kV, 40 A, 2θ=15°-65°). X-ray photoelectron spectroscopy (XPS, Thermo VG, ESCALAB250) was employed to determine the elemental composition and chemical states of the materials. Electrochemical measurements were performed on an electrochemical workstation (CHI 660E). The catalytic ability of the material was evaluated by Tafel plot measurements, which were recorded using a symmetrical two-electrode cell at a scan rate of 20 mV·s^-1 from -0.7 to 0.7 V. CV curves were recorded in a three-electrode system at a scan rate of 10 mV·s^-1. EIS was conducted in the frequency range of 0.1 Hz to 100 kHz to measure the parameters of the DSSCs. The photocurrent density-voltage (J-V) characteristics were measured under AM 1.5G simulated sunlight (100 mW·cm^-2) using a solar simulator (91160, Oriel, Newport, USA).

  2.   Results and discussion

  2.1   Appearance characterization

  SEM can be used to observe the microscopic morphology of the composite, while TEM can further characterize the structure of the morphology. Fig.1a shows the CC before hydrothermal growth. The surface was very smooth, and the arrangement was relatively regular. Fig.1b-1e showed that FMS was successfully and evenly attached to the surface of CC after hydrothermal reaction. The diameter of CC was 9.454 μm, and the diameter of a single root FMS/CC reached 13.64 μm after hydrothermal growth. At the same time, the columnar structure with an irregular tip and rough surface can be seen by magnification. Compared with pure CC, FMS/CC possessed a larger specific surface area and an increased number of active sites. As shown in Fig.1f, the FMS synthesized without a CC substrateexhibited severe agglomeration, which is detrimental to its catalytic performance as a CE. During TEM sample preparation, FMS was stripped off from the CC using ultrasound. It can be seen from Fig.1g-1i that the surface of the morphology was rough, the tip was irregular, and there was no diffraction lattice, indicating that FMS had an amorphous structure. Fig.1j-1m indicated that the tested FMS contained Fe, Mo, and S elements.

  Figure 1

  

  Figure 1.  SEM images of (a) CC, (b-e) FMS/CC, and (f) pure FMS synthesized without CC; (g, h) TEM and (i) HRTEM images, and (j-m) element mappings of FMS/CC

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  2.2   Phase structure analysis

  Fig.2a shows the XRD patterns of FMS/CC and FeOOH/CC. The diffraction peaks of 16.5°, 26.5°, 35.6°, 39.3°, 46.1°, 52.3°, 55.8°, and 64.9° of the precursor FeOOH/CC are correlated with FeOOH (PDF No.97-1136), corresponding to crystal planes of (200), (130), (211), (301), (411), (600), (251), and (541), respectively^[32], and the diffraction peak at 26.5° corresponds to the (002) plane of graphitic carbon^[33]. There were no other peaks in the XRD pattern of FMS/CC after vulcanization except the characteristic peak of CC and two rather wide "rise peaks" (diffuse reflection peaks), which is a typical feature of solid amorphous^[34-35], indicating that the precursor FeOOH/CC became amorphous after being vulcanized by(NH₄)₂MoS₄, corresponding to the TEM characterization above. Fig.2b is the energy dispersive X-ray spectrum (EDS) of FMS/CC, which can directly obtain the types and relative contents of elements on the surface of the sample. FMS/CC only contained four elements (S, C, Mo, and Fe). In addition, the atomic ratio of Fe, Mo, and S elements was approximately 1:1:4, which is consistent with the stoichiometric ratio of FeMoS₄, while the C element was from CC.

  Figure 2

  

  Figure 2.  (a) XRD patterns of FMS/CC and FeOOH/CC; (b) EDS of FMS/CC

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  2.3   XPS characterization

  To further verify the synthesis of FMS/CC and the valence states of the contained elements^[36], XPS was used. Fig.3a indicated that there were only C, O, S, Mo, and Fe. Fig.3b shows the Mo3d spectrum, the peaks correspond to the Mo3d_5/2 at 229.3 eV and the Mo3d_3/2 at 233.0 eV. The peak at 236.2 eV proves the presence of Mo⁶⁺ in the sample^[37]. The Fe2p spectrum (Fig.3c) had two main peaks of Fe²⁺2p_3/2 and Fe²⁺2p_1/2 appeared at the binding energies of 711.8 and 725.9 eV^[38]. The S2p spectrum (Fig.3d) reveals the S^2-, characterized by the S2p_3/2 and S2p_1/2 spin-orbit doublet at 162.1 and 163.3 eV, respectively, along with a satellite peak (Sat.) at 164.5 eV^[39]. The XPS analysis and the above characterization can fully indicate the successful synthesis of FMS/CC with an amorphous structure.

  Figure 3

  

  Figure 3.  (a) Survey, (b) Mo3d, (c) Fe2p, and (d) S2p XPS spectra of FMS/CC

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  2.4   CV analysis

  Fig.4a and 4b display the CV curves of a three-electrode test system to characterize the electrocatalytic activity of FMS/CC on CEs with different film thicknesses^[40]. In Fig.4a, the two pairs of redox peaks can be identified regardless of film thickness, indicating analogous catalytic activity with Pt materials. The cathode peak current density (J_pc) reflects the catalytic performance of the material for I₃^-. |J_pc| from large to small was FMS/CC-3 > FMS/CC-2 > FMS/CC-4 > FMS/CC-5 > FMS/CC-1 > Pt, where the maximum |J_pc| value of FMS/CC-3 was about 7.5 mA·cm^-2, and all of FMS/CC-x were larger than the Pt CE. This indicates that FMS/ CC-3 is more conducive to the reduction reaction of I₃^- and has better electrocatalytic activity. The peak-to-peak potential separation (E_pp), a measure of electrocatalytic kinetics, was found to be inversely correlated with the |J_pc|. The FMS/CC-3 CE demonstrated the smallest E_pp, signifying the most facile kinetics and the highest catalytic activity for the I₃^-/I^- redox reaction, which is essential for efficient triiodide reduction at the CE. Fig.4b shows the CV curves of FMS/CC-x tested continuously for 100 cycles. It can be seen that the CV curve remained unchanged, and there were two pairs of obvious redox peaks, indicating that FMS/CC not only had good reversibility when used as a DSSC CE, but also was very stable in the electrolyte containing I₃^-/I^-. It is not easy to be corroded and dissolved, which fully indicates that the electrocatalytic activity of FMS/CC-3 was the highest and stable when the film thickness of the CE was 13 μm.

  Figure 4

  

  Figure 4.  (a) CV curves of the CEs; (b) CV curves of the FMS/CC-3 CE for the 1st and 100th cycles

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  2.5   EIS analysis

  Three important parameters, namely interface charge transfer resistance (R_ct), R_s, and I₃^-/I^- electron pair diffusion impedance (Z_N) in the electrolyte, can be obtained by EIS (Fig.5a). The inset in Fig.5a presents the equivalent circuit used for fitting, with C_μ representing the interfacial double-layer chemical capacitance. Table 1 lists the specific values. The higher R_s of the Pt CE is attributed to its use of a high-resistance FTO substrate, in contrast to the FMS/CC-x CEs, which is fabricated on a more conductive titanium mesh. In addition, since the thickness of the CE will also affect R_s, the R_s was sorted from large to small as follows: Pt > FMS/CC-5 > FMS/CC-4 > FMS/CC-3 > FMS/CC-2 > FMS/CC-1 based on Fig.5a. Generally, the radius of the first-class semicircle represents the R_ct value, and the smaller the radius, the smaller the R_ct value, indicating that the CE material had excellent catalytic performance in reducing I₃^-. It can be seen from the figure that the order of R_ct from small to large was FMS/CC-3 < FMS/ CC-2 < FMS/CC-4 < FMS/CC-5 < FMS/CC-1 < Pt, indicating that FMS/CC-3 was more conducive to the reduction of I₃^- on the CE. If the film thickness is too thin, the reduction of I₃^- cannot be more effective, so the R_ct will be larger. With the increase of the thickness of the CE film, although the active material increases, it will also increase R_s, and cause the CE surface to crack. The harm brought by this situation is far greater than the benefit brought by the increase of active substances, which is not conducive to the transfer of charge. The Z_N is approximately equal to the radius of the second-class semicircle, and the smaller Z_N indicates that I₃^-/I^- diffuses more rapidly in the electrolyte, resulting in a larger diffusion coefficient. The film thickness of FMS/CC-3 is more conducive to the diffusion of iodine ions, and too thick or too thin film thickness will reduce Z_N. According to EIS analysis, when the film thickness of FMS/CC was 13 μm, it had the smallest R_ct and Z_N, and the largest electrocatalytic activity, as verified by the verification results of CV.

  Figure 5

  

  Figure 5.  EIS of (a) FMS/CC-x and (b) Pt CEs

  Inset: corresponding equivalent circuit diagram.

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  Table 1

  

  Table 1.  EIS parameters of the CEs

  下载: 导出CSV

  CE	Rs / (Ω·cm2)	Rct / (Ω·cm2)	ZN / (Ω·cm2)
  FMS/CC-1	2.46	0.25	0.11
  FMS/CC-2	2.48	0.05	0.02
  FMS/CC-3	2.50	0.03	0.01
  FMS/CC-4	2.54	0.07	0.03
  FMS/CC-5	2.55	0.13	0.05
  Pt	12.17	4.25	0.45

  2.6   Tafel plots

  The Tafel polarization test is also a method for evaluating the electrochemical performance of CE materials, which can obtain the limiting diffusion current density (J_lim) and exchange current density (J₀). Fig.6a shows the Tafel plots of FMS/CC-x. It can be seen that the J_lim of FMS/CC-3 was the largest, about 2.40 mA·cm^-2, and the minimum of the Pt CE was about 1.74 mA·cm^-2, and that of the other CEs was larger than that of the Pt CE. This indicates that using titanium mesh as a conductive carrier is beneficial for the diffusion of iodine electrons in the electrolyte, suggesting that the more porous the titanium mesh, the higher the diffusion coefficient, which is due to its porous structure. But if the CE film is too thick, it will cause surface cracking, indirectly hindering the transmission of iodine ions, and thus reducing J_lim. Another important parameter, J₀, is inversely proportional to R_ct in EIS. The larger the J₀, the stronger the iodine reduction catalytic performance of the CE. The intersection point between the slope of the cathode branch (polarization region) and the equilibrium potential was denoted as J₀ and the J₀ from large to small was FMS/CC-3 > FMS/CC-2 > FMS/CC-4 > FMS/CC-5 > FMS/CC-1 > Pt, so FMS/CC-3 had a largest J_lim and J₀, indicating that FMS/CC-3 had the best catalytic activity. This is consistent with the above conclusions of CV and EIS.

  Figure 6

  

  Figure 6.  (a) Tafel plots and (b) J-V curves of FMS/CC-x and Pt CEs

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  2.7   J-V curves for CEs

  The photoelectric performance of the CEs with different film thicknesses were tested^[29], and the results are displayed in Fig.6b. It can be seen that there was little difference in open-circuit voltage (V_oc), which is because the light anode used in the test was the same batch, so the V_oc value was within a certain range; the short-circuit current density (J_sc) in descending order was FMS/CC-3 > FMS/CC-2 > FMS/CC-4 > FMS/CC-5 > FMS/CC-1 > Pt. The J_sc values of the other CEs, except FMS/CC-1, were greater than Pt. This is attributed to the growth of FMS/CC, which provides a larger specific surface area and a greater number of active sites, thereby resulting in superior catalytic activity compared to the Pt CE. As can be seen from the table, the maximum J_sc of the FMS/CC-3 CE was about 18.31 mA·cm^-2. When the film thickness is too thin, the CE will be unable to catalyze the reoxidation reaction better due to the lack of catalytic materials, so the J_sc will be reduced. When the film thickness is too thick, although the required active material is increased, the distance between the CE and the electrolyte increases, but the R_ct becomes larger, and the surface and interior of the CE film are prone to cracking, and even lead to falling off, which will greatly increase the R_s value, and ultimately make the J_sc smaller. The porous titanium mesh with lower self-resistance was used as the conductive carrier for the FMS/CC-x CEs. Therefore, combined with the above analysis, the smaller the R_ct and R_s of the CE, the larger the fill factor (FF) of the CE, as shown in Table 2. Finally, through the comparison of the above groups of experiments, when the film thickness was 13 μm, the V_oc of FMS/CC-3 was about 0.79 V, the J_sc was about 18.31 mA·cm^-2, the FF was about 0.65, and the PCE was about 9.51%.

  Table 2

  

  Table 2.  Photovoltaic performance parameters of DSSCs

  下载: 导出CSV

  CE	Voc / V	Jsc / (mA·cm-2)	FF	PCE / %
  FMS/CC-1	0.782±0.008	16.54±0.03	0.66±0.02	8.56±0.05
  FMS/CC-2	0.796±0.002	17.90±0.02	0.65±0.02	9.28±0.04
  FMS/CC-3	0.796±0.002	18.31±0.02	0.65±0.02	9.51±0.02
  FMS/CC-4	0.792±0.002	17.56±0.02	0.66±0.03	9.14±0.03
  FMS/CC-5	0.782±0.008	16.99±0.03	0.66±0.02	8.79±0.01
  Pt	0.796±0.004	15.58±0.02	0.61±0.03	7.81±0.03

  3.   Conclusions

  In this work, amorphous FMS/CC composites were successfully synthesized on CC via a two-step hydrothermal method. The composite synergistically combines the high electrical conductivity of the CC scaffold with the efficient catalytic performance of FMS, effectively overcoming the inherent limitations of the individual components, namely the lack of active sites in pure CC and the severe agglomeration of pure FMS. SEM and TEM analyses reveal that the FeMoS₄ material forms a uniform, vertically aligned columnar structure on the CC. This morphology provides a significantly larger specific surface area and a greater number ofactive sites compared to pure CC. Furthermore, this study demonstrates that the film thickness is a critical parameter for photovoltaic performance. Through systematic optimization, the FMS/CC-3 CE with a film thickness of 13 μm exhibited the highest electrocatalytic activity, enabling the corresponding DSSCs to achieve a PCE of about 9.51%.

  
  Acknowledgements: National Natural Science Foundation of China (NSFC) (Grant No.52271209), Funded by Science Research Project of Hebei Education Department (Grant No.JCZX2025019), and Supported by Interdisciplinary Research Program of Hebei University (Grant No.DXK202401).
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  Scheme 1  Fabrication process of the DSSC CE with the FMS/CC composite

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  Figure 1  SEM images of (a) CC, (b-e) FMS/CC, and (f) pure FMS synthesized without CC; (g, h) TEM and (i) HRTEM images, and (j-m) element mappings of FMS/CC

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  Figure 2  (a) XRD patterns of FMS/CC and FeOOH/CC; (b) EDS of FMS/CC

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  Figure 3  (a) Survey, (b) Mo3d, (c) Fe2p, and (d) S2p XPS spectra of FMS/CC

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  Figure 4  (a) CV curves of the CEs; (b) CV curves of the FMS/CC-3 CE for the 1st and 100th cycles

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  Figure 5  EIS of (a) FMS/CC-x and (b) Pt CEs

  Inset: corresponding equivalent circuit diagram.

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  Figure 6  (a) Tafel plots and (b) J-V curves of FMS/CC-x and Pt CEs

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  Table 1.  EIS parameters of the CEs

  CE	Rs / (Ω·cm2)	Rct / (Ω·cm2)	ZN / (Ω·cm2)
  FMS/CC-1	2.46	0.25	0.11
  FMS/CC-2	2.48	0.05	0.02
  FMS/CC-3	2.50	0.03	0.01
  FMS/CC-4	2.54	0.07	0.03
  FMS/CC-5	2.55	0.13	0.05
  Pt	12.17	4.25	0.45

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  Table 2.  Photovoltaic performance parameters of DSSCs

  CE	Voc / V	Jsc / (mA·cm-2)	FF	PCE / %
  FMS/CC-1	0.782±0.008	16.54±0.03	0.66±0.02	8.56±0.05
  FMS/CC-2	0.796±0.002	17.90±0.02	0.65±0.02	9.28±0.04
  FMS/CC-3	0.796±0.002	18.31±0.02	0.65±0.02	9.51±0.02
  FMS/CC-4	0.792±0.002	17.56±0.02	0.66±0.03	9.14±0.03
  FMS/CC-5	0.782±0.008	16.99±0.03	0.66±0.02	8.79±0.01
  Pt	0.796±0.004	15.58±0.02	0.61±0.03	7.81±0.03

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