Reduced Graphene Oxide Counter Electrode Research Articles

Facile fabrication of reduced graphene oxide counter electrodes by laser engraver for dye-sensitized solar cell applications

Exploring alternative Pt-free counter electrode with low cost and high electrocatalytic activity is always a main focus at the frontier of dye-sensitized solar cells (DSSCs). In this study, a desktop laser engraver was applied to reduce graphene oxide (GO) film on a fluorine-doped tin oxide (FTO) substrate, and the obtained graphene-based material was further used as counter electrode for DSSC. Additionally, this facile laser-scribing method was also adopted to fabricate a prototype of composite electrode via the combination of reduced graphene oxide (RGO) and carbon black (CB) to enhance the specific surface area and active sites. A variety of characterizations including scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were conducted to investigate the microstructures and catalytic properties of these carbon electrodes. The findings reveal that both of the DSSCs with laser-scribed carbon electrodes show evidently increasing photovoltaic performance, and the DSSC based on RGO/CB composite electrode even presents a higher power conversion efficiency (PCE) of 4.49%, comparable to 4.14% of the conventional Pt-based DSSC.

Facile Synthesis of CoNi Bimetallic Nanoparticle Decorated Reduced Graphene Oxide as Efficient and Low-Cost Counter Electrode for Dye-Sensitized Solar Cells.

In this paper, CoNi bimetallic nanoparticle decorated reduced graphene oxide (CoNi-RGO) was synthesized by a facile hydrothermal method. When applied this CoNi-RGO into counter electrode for dye-sensitized solar cells (DSSCs), it shows smaller charge-transfer resistance and better electrocatalytic activity than that of pure reduced graphene oxide (RGO). At the optimized conditions, the energy conversion efficiency of DSSCs based on CoNi-RGO counter electrode was 3.79%, indicating a higher photovoltaic performance of DSSCs based on CoNi-RGO counter electrode than that of DSSCs based on RGO counter electrode (1.37%), and comparable to the value of DSSCs based on Pt counter electrode as a reference (4.95%). Additionally, the photovoltaic performance of DSSCs based on CoNi-RGO counter electrode strongly depends on its composition. The molar ratio of Co/Ni and the weight ratio of CoNi/GO that used to prepare CoNi-RGO counter electrode are key factors to affect the performance of their cell devices. When both the molar ratio of Co/Ni and the weight ratio of CoNi/GO are 1:1, the CoNi-RGO counter electrode shows the best performance, indicating the potential of such bimetallic nanoparticle decorated RGO as low-cost and efficient counter electrode to replace noble metal Pt counter electrode for the practical application of DSSCs devices.

Synthesis of an Efficient Counter Electrode Material for Dye-Sensitized Solar Cells by Pyrolysis of Melamine and Graphene Oxide.

An efficient counter electrode material for dye sensitized solar cells (DSSCs) was synthesized by pyrolysis of melamine and graphene oxide. The synthesized samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electrode microscopy, which show that nitrogen doped reduced graphene oxide (NRGO) was obtained by this synthesis method. In the synthesized NRGO, graphitic structure was kept and the nitrogen was existence as pyrrolic, pyridinic, graphitic, and oxidized nitrogen species in the samples. After deposited as counter electrode films for DSSCs, it shows lower charge-transfer resistance at the electrode/electrolyte interface and higher electrocatalytic activity towards reduction of triiodide (I-₃) than that of reduced graphene oxide (RGO) prepared also by this method without adding melamine. Consequently, the DSSCs based on NRGO counter electrodes achieve an energy conversion efficiency of 4.60%, which is higher than that of RGO counter electrode (2.35%). Although the photovoltaic performance of NRGO counter electrode was lower than that of Pt counter electrode (5.70%), it is still a promising counter electrode to replace noble metal Pt due to its low cost and simple synthesis process.

MoS2 nanosheets based counter electrodes: An alternative for Pt-free dye-sensitized solar cells

Dye-sensitized solar cells are assembled with MoS2 nanosheets based counter electrodes synthesized via hydrothermal route using ammonium molybdate tetrahydrate and thiourea as precursor materials. Basic and specific studies are followed to characterize MoS2 as counter electrode material by XRD, SEM, TEM, EDX, cyclic voltammetry and electrochemical impedance spectroscopic studies. Dye-sensitized solar cells device is fabricated by using fluorine-doped tin oxide glass plate coated with TiO2 as photoanode, Cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) dye as a light harvester, and iodine/iodide as a liquid electrolyte. The fabricated dye-sensitized solar cells device with MoS2 counter electrode showed an open circuit voltage of 795 mV, short circuit current of 19.6 mA/cm2, fill factor of 0.36, and power conversion efficiency of 6.6% upon comparing to Pt counter electrode which showed an open circuit voltage of 827 mV, short circuit current of 14.8 mA/cm2, fill factor of 0.47, and power conversion efficiency of 6.8%. In addition to this, MoS2 coupled reduced graphene oxide counter electrodes are prepared by simply dispersing reduced graphene oxide and MoS2 in isopropyl alcohol which showed the best performance with open circuit voltage of 800 mV, short circuit current of 20.5 mA/cm2, fill factor of 0.42, and power conversion efficiency of 8.1%.

Dye‐sensitised solar cell utilising gold doped reduced graphene oxide counter electrode: influence of annealing time

Gold doped reduced graphene oxide (rGO) films prepared via hummer method have been utilised as counter electrode of dye-sensitised solar cell. The samples were subjected to various annealing times at 120°C. The effect of annealing time on the dark current and photovoltaic performance has been investigated. The power conversion efficiency varies with annealing time. The highest efficiency of 0.155% was achieved by the device utilising gold doped rGO annealed for 45 min. This is due to the device employing this sample possesses the smallest leak current.

Effect of Annealing Temperature of Gold Doped Reduced Graphene Oxide Counter Electrode on the Performance of Dye-sensitized Solar Cell

Effect of Annealing Temperature of Gold Doped Reduced Graphene Oxide Counter Electrode on the Performance of Dye-sensitized Solar Cell

Incorporating MoFe alloys into reduced graphene oxide as counter electrode catalysts for dye-sensitized solar cells

In this study, MoFe alloy decorated onto reduced graphene oxide (RGO) nanohybrids is successfully synthesized with various volume ratios of Fe to Mo precursors using a dry plasma reduction method at a low temperature and under atmospheric pressure and is introduced for the first time as an electrocatalyst for counter electrodes (CEs) in dye-sensitized solar cells (DSCs). As observed by HRSEM and TEM analyses, MoFe is successfully immobilized on a 3D network structure of RGO. Well-dispersed MoxFe1−x (0 ≤ x ≤ 1) NPs ranging in size from 2 to 6 nm are stabilized with RGO after co-reduction of the metal precursor ions and graphene oxide. The developed catalysts are then applied as CEs in DSCs. As a result, the Mo0.7Fe0.3/RGO nanohybrid exhibited the highest electrocatalytic activity, corresponding to the lowest charge transfer resistance of 0.11 Ω, among the electrodes tested. The DSC employing Mo0.7Fe0.3/RGO CEs exhibits 5.44% efficiency, which is higher than the 1.26, 4.54 and 4.53% efficiency rates for cells using RGO, Mo0Fe1/RGO and Mo1Fe0/RGO electrodes, respectively, due to the optimization of the catalytic activity and the electron conductivity of the developed materials. Note that the efficiency of the device using a Pt electrode was 5.36% under identical conditions. This study concludes that the CE based on the MoFe/RGO nanohybrid is a prospective substitute for Pt which can provide new opportunities for advancing high-efficiency DSCs. Furthermore, the developed catalysts can be applied to other applications, such as methanol oxidation and oxygen reduction reactions.

FeSn alloy/graphene as an electrocatalyst for the counter electrode of highly efficient liquid-junction photovoltaic devices

This study presents the synthesis of FexSn1-x alloys (0 ≤ x ≤ 1)/reduced graphene oxide (RGO) using a dry plasma reduction method. The formation of bimetallic FeSn nanoparticles on the surface of RGO was confirmed through TEM and XRD measurements. In the results, FeSn ranging from 1 to 5 nm in size is shown to be successfully immobilized on the RGO surface. The developed materials are then applied as Pt-free counter electrodes (CEs) in liquid-junction photovoltaic devices. To get efficient CEs, we have carefully controlled the chemical composition of the FexSn1-x/RGO through changing the volume ratio of the Fe and Sn precursors during synthesis. The catalytic activity of the electrodes follows the sequence of Fe0.1Sn0.9/RGO > Fe0Sn1/RGO > Fe0.3Sn0.7/RGO > Fe0.5Sn0.5/RGO > Fe0.7Sn0.3/RGO > Fe0.9Sn0.1/RGO > Fe1Sn0/RGO, with the Zw values of the developed electrodes lower than those of Sn/RGO and Fe/RGO electrodes. Accordingly, the highest efficiency was 5.0% for the device using Fe0.1Sn0.9/RGO CE, which is also higher than those of devices using Sn/RGO (4.6%) and Fe/RGO (3.8%). The proposed strategy is simple and efficient and is, therefore, promising for the fabrication of cost-effective CE materials for next-generation solar cells and lithium-ion batteries.

Understanding Catalytic Behavior of Co-Sn Alloy/Graphene Counter Electrode Electrocatalysts in Liquid-Junction Photovoltaic Devices

Understanding the electrocatalytic activity of counter electrode (CE) favors to tune the sluggish triiodide reduction kinetics and to compare their catalytic activities. We present here the synthesis of CoXSn1-X alloys (0 ≤ X ≤ 1) on reduced graphene oxide (RGO) under atmospheric pressure plasma without using any toxic chemical reagents. The developed materials are then applied as catalysts for the reduction of triiodide ions to iodide ions in CE of dye-sensitized solar cells (DSCs). It should be noted that the triiodide reduction reaction is one of the utmost significances in the advanced electrochemical energy conversion of DSCs. Therefore, insights into the relationship between alloy composition, electronic structure and catalytic activity should be carefully determined in this study. As the TEM measurements, CoSn nanoparticles with size in the range of 1-5 nm is successfully immobilized on the surface of RGO. Electrochemical catalytic activity performances indicate that the Co0.9Sn0.1/RGO gave the highest catalytic activity compared other electrodes which were determined by the lowest charge-transfer resistance and diffusion impedance values. Thus, the highest power conversion efficiency was obtained for the device using Co0.9Sn0.1/RGO CE. The strategy has a great promise in developing high-performance DSCs and the launched reduction rate constant having commonality in comparing the catalytic activity of CE electrocatalysts.

Facile synthesis of nitrogen-doped reduced graphene oxide as an efficient counter electrode for dye-sensitized solar cells

A nitrogen-doped reduced graphene oxide (N-RGO) nanosheet was synthesized by a simple hydrothermal method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electrode microscopy. After being deposited as counter electrode film for dye-sensitized solar cells (DSSCs), it is found that the synthesized N-RGO nanosheet has smaller charge-transfer resistance and better electrocatalytic activity towards reduction of triiodide than the reduced graphene oxide (RGO) nanosheet. Consequently, the DSSCs based on the N-RGO counter electrode achieve an energy conversion efficiency of 4.26%, which is higher than that of the RGO counter electrode (2.85%) prepared under the same conditions, and comparable to the value (5.21%) obtained with the Pt counter electrode as a reference. This N-RGO counter electrode offers the advantages of not only saving the cost of Pt itself but also simplifying the process of counter electrode preparation. Therefore, an inexpensive N-RGO nanosheet is a promising counter electrode material to replace noble metal Pt.

Pt-free counter electrode based on FeNi alloy/reduced graphene oxide in liquid junction photovoltaic devices

This study presents a strategy to optimize FeNi nanoparticles (NPs) deposited onto reduced graphene oxide (RGO) in order to fabricate an efficient Pt-free counter electrode (CE) for use in a dye-sensitized solar cell (DSC). Nanohybrids exhibit a 3D network structure of RGO with high FeNi NP loading on the RGO surface. Well-dispersed Fe1-xNix (0 ≤ x ≤ 1) NPs ranging in size from 2 to 4 nm are stabilized with RGO after co-reduction of the metal precursor ions and graphene oxide. The developed catalysts are then applied as CEs in DSCs. As a result, the Fe0.7Ni0.3/RGO nanohybrid exhibited the highest electrocatalytic activity, corresponding to the lowest charge transfer resistance of 0.17 Ω, among the electrodes tested. The DSC employing Fe0.7Ni0.3/RGO CEs exhibits increases in efficiency of 87.68% and 75.65% relative to those of Fe0Ni1/RGO and Fe1Ni0/RGO devices, respectively, due to the optimization of the charge-transfer resistance and the reduced diffusion impedance values of the developed materials. This strategy is simple and efficient for fabricating cost-effective CE materials utilized in DSCs and fabricating efficient catalysts to facilitate methanol oxidation and oxygen reduction reactions.

Improving the photovoltaic performance of DSSCs using a combination of mixed-phase TiO2 nanostructure photoanode and agglomerated free reduced graphene oxide counter electrode assisted with hyperbranched surfactant

The role of hyperbranched surfactant, namely, sodium 1,4-bis (neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate (TC14), in the synthesis and stabilisation of reduced graphene oxide (rGO) as counter electrode (CE) thin film was investigated for dye-sensitised solar cell (DSSCs) application. The energy conversion efficiency (η) of CE-based rGO from TC14 (TC14-rGO) was 0.0266%, with a short current density, open circuit voltage and fill factor of 0.222 mA/cm2, 0.697 V and 14.15, respectively. The efficiency of the surfactant was two times higher than that of CE-based rGO from single-tail sodium dodecyl sulphate surfactant. Graphene oxide (GO) was initially synthesised by electrochemical exfoliation method. Hydrazine hydrate was subsequently used in the production of rGO through chemical reduction process. Spraying deposition method was used to transfer GO and rGO solutions and fabricate GO and rGO CE thin films. A novel combination of hydrothermal growth and squeegee method in the synthesis and production of mixed-phase titanium dioxide (TiO2) nanostructures as photoanode was selected due to its simple and low-cost method. Rutile TiO2 nanorods and anatase TiO2 nanoparticles are essential in electron transfer process and dye adsorption, respectively. Therefore, these combinations resulted in improved photocatalytic activity and η of dye-sensitised solar cells when TC14-rGO was used.

Design of CoNi alloy/graphene as an efficient Pt-free counter electrode in liquid junction photovoltaic devices

CoxNi1-x alloys (0≤x≤1) are successfully synthesized and immobilized on a reduced graphene oxide (RGO) surface using the dry plasma reduction method. HRSEM and XPS measurements are used to analyze the morphology and chemical composition of the developed materials. Then, the developed materials are applied as Pt-free counter electrodes (CEs) in liquid junction photovoltaic devices. In order to obtain efficient CEs, the chemical composition of the CoxNi1-x/RGO is controlled through optimizing the volume ratio of the Co and Ni precursors during the synthesizing process. It is found that the highest efficiency was 6.75% for the device using Co0.3Ni0.7/RGO CE, which is also higher than those of the devices using Pt CE (6.63%), Co/RGO (6.33%), and Ni/RGO (5.52%). The obtained results can be explained through the optimization of the charge-transfer resistance and diffusion impedance values of the developed materials. The strategy is simple and efficient; thus, it is promising for fabricating cost-effective CE materials for dye-sensitized solar cells.

Cost-effective CoPd alloy/reduced graphene oxide counter electrodes as a new avenue for high-efficiency liquid junction photovoltaic devices

Abstract This work presents the synthesis of Co x Pd 1-x alloys (0 ≤ x ≤ 1) on a reduced graphene oxide (RGO) surface using the dry plasma reduction method. The formation of CoPd alloys on the RGO surface is confirmed through high-resolution scanning electron microscopy (HRSEM) and X-ray photoelectron spectroscopy (XPS) measurements, and transmittance electron microscopy (TEM). Then, the developed materials are applied as Pt-free counter electrodes (CEs) in dye-sensitized solar cells (DSCs). In order to obtain efficient CEs, the chemical composition of the Co x Pd 1-x /RGO is controlled through optimizing the volume ratio of the Co and Pd precursors during the synthesizing process. Due to the optimization of the charge-transfer resistance ( R ct ) and the diffusion impedance ( Z w ) values of the Co 0.9 Pd 0.1 /RGO CE, the device using the Co 0.9 Pd 0.1 /RGO CE exhibits the highest efficiency among the fabricated cells. Note that the cells using Co/RGO and Pd/RGO exhibit efficiencies of 5.17% and 5.41%, respectively. The proposed strategy is simple and efficient; thus, it is promising for fabricating highly efficient and low-cost CE materials for DSCs.

Pt-free spray coated reduced graphene oxide counter electrodes for dye sensitized solar cells

Graphene oxide (GO) was synthesized using a modified Hummers method and was reduced by using focused sunlight to obtain solar reduced graphene oxide (SRGO). GO and SRGO are then used as Pt-free counter electrode materials in dye sensitized solar cells (DSSCs). GO and SRGO counter electrodes were prepared by a simple spray coating method to produce homogeneous electrode layers. The DSSCs with GO and SRGO counter electrodes exhibited an overall power conversion efficiencies of ∼3.4 and ∼4%, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the DSSC with SRGO counter electrode exhibits higher electro-catalytic activity and lower charge transfer resistance at the electrode/electrolyte interface (in comparison to the DSSC with GO) resulting in higher conversion efficiency. Moreover, the microstructural features of SRGO are found to be suitable for its improved interaction with the liquid electrolyte and the enhanced electro-catalytic activity at its surface.

Unique ZnS nanobuns decorated with reduced graphene oxide as an efficient and low-cost counter electrode for dye-sensitized solar cells

Unique ZnS nanobuns decorated with reduced graphene oxide (RGO) was synthesized and found to exhibit a synergetic effect as a highly efficient and low-cost counter electrode (CE) in dye-sensitized solar cells (DSCs). Using this ZnS-RGO CE, a power conversion efficiency (PCE) of 7.03% was achieved. This value was 53% and 41% higher than those of pure ZnS and RGO CEs, respectively. The ZnS-RGO nanocomposite is indeed an efficient and cost-effective Pt-like alternative for iodine reduction reaction.

Rapid atmospheric pressure plasma jet processed reduced graphene oxide counter electrodes for dye-sensitized solar cells.

In this work, we present the use of reduced graphene oxide (rGO) as the counter electrode materials in dye-sensitized solar cells (DSSCs). rGO was first deposited on a fluorine-doped tin oxide glass substrate by screen-printing, followed by post-treatment to remove excessive organic additives. We investigated the effect of atmospheric pressure plasma jet (APPJ) treatment on the DSSC performance. A power conversion efficiency of 5.19% was reached when DSSCs with an rGO counter electrode were treated by APPJs in the ambient air for a few seconds. For comparison, it requires a conventional calcination process at 400 °C for 15 min to obtain comparable efficiency. Scanning electron micrographs show that the APPJ treatment modifies the rGO structure, which may reduce its conductivity in part but simultaneously greatly enhances its catalytic activity. Combined with the rapid removal of organic additives by the highly reactive APPJ, DSSCs with APPJ-treated rGO counter electrode show comparable efficiencies to furnace-calcined rGO counter electrodes with greatly reduced process time. This ultrashort process time renders an estimated energy consumption per unit area of 1.1 kJ/cm(2), which is only one-third of that consumed in a conventional furnace calcination process. This new methodology thus saves energy, cost, and time, which is greatly beneficial to future mass production.

Effects of hydrazine hydrate treatment on the performance of reduced graphene oxide film as counter electrode in dye-sensitized solar cells

The reduced graphene oxide (RGO) counter electrodes were prepared by drop casting method and followed by heat treatment. The as-prepared RGO counter electrodes were used as substitution for Pt counter electrode in dye-sensitized solar cells (DSSCs). The effects of hydrazine hydrate in graphene oxide (GO) suspension on the performance of RGO counter electrodes were investigated. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that a moderate amount of hydrazine hydrate can enhance the catalytic activity of the RGO film toward the reduction of I3− and decrease the sheet resistance of the film. The efficiency (η) of DSSC based on the RGO counter electrodes with optimum addition of hydrazine hydrate increased from 1.826% to 2.622% under a simulated solar illumination of 100mWcm−2 (AM 1.5).

Fabrication and Characterization of Reduced Graphene Oxide Counter Electrode for Dye-Sensitized Solar Cells

To improve performance of dye-sensitized solar cell(DSSC), thermally reduced graphene oxide(rGO) was investigated as Pt-free counter electrodes(CE) material. The DSSCs with rGO were fabrcated by simple spin coating method under different temperature and ambient atmospheres like Ar, N2 and air. When the rGO CE was reduced at 450°C under the Ar atmosphere, it was obtained the power conversion efficiency of 6.02%, which showed the high catalytic activity and performance of DSSC as much as Pt. This value means the thermally reduced rGO CEs under the Ar gas will be suitable as a substitute for Pt CEs.

Highly Efficient Metal-Free Sulfur-Doped and Nitrogen and Sulfur Dual-Doped Reduced Graphene Oxide Counter Electrodes for Dye-Sensitized Solar Cells

Developing metal-free electrocatalysts with both high performance and low cost for the reduction reaction at the cathode of dye-sensitized solar cells (DSCs) is critical for further cost reduction and large-scale implementation of DSCs. Here, sulfur-doped reduced graphene oxide (SRGO) and nitrogen and sulfur dual-doped reduced graphene oxide (NSRGO) were applied as highly efficient metal-free electrocatalysts for DSCs in disulfide/thiolate redox electrolytes. It was found that SRGO and NSRGO exhibited outstanding electrochemical performance toward catalyzing the disulfide/thiolate redox couple. The DSC devices based on SRGO and NSRGO counter electrodes showed power conversion efficiency of 4.23% and 4.73%, respectively. In addition, the obtained SRGO and NSRGO also presented catalytic activity higher than that of the platinum electrodes for Co(bpy)33+/2+ redox mediators. The currently reported SRGO and NSRGO demonstrate not only the attractive feasibility of replacing platinum cathodes with abundant carbon materials for novel iodine-free electrolytes but also that the judicious heteroatom doping of graphene oxide might open promising directions for further cathode candidates for iodine-free DSCs.