Search Results (15)

In the present mini-review article, we have compiled the previously reported literature on the fabrication of MXenes and their hybrid composite materials based electrochemical sensors for the determination of phenolic compounds and counter electrodes for platinum (Pt)-free dye-sensitized solar cells (DSSCs). MXenes are two-dimensional (2D) materials with excellent optoelectronic and physicochemical properties. MXenes and their composite materials have been extensively used in the construction of electrochemical sensors and solar cell applications. In this paper, we have reviewed and compiled the progress in the construction of phenolic sensors based on MXenes and their composite materials. In addition, co1.unter electrodes based on MXenes and their composites have been reviewed for the development of Pt-free DSSCs. We believe that the present review article will be beneficial for the researchers working towards the development of phenolic sensors and DSSCs using MXenes and their composites as electrode materials. Full article

Conducting polymers are emerging as promising alternatives to rare and expensive platinum for counter electrodes in dye-sensitized solar cells; due to their ease of synthesis, they can be chemically tuned and are suitable for roll-to-roll production. Among these, poly (3,4-ethylenedioxythiophene) (PEDOT)-based counter electrodes have shown leading photovoltaic performance. However, certain conductivity issues remain that affect the effectiveness of these counter electrodes. In this study, we present an electropolymerized PEDOT and poly(N-alkylated-carbazole) copolymer as an efficient electrocatalyst for the reduction in ${\mathrm{I}}_3^{-}$ in dye-sensitized solar cells. Copolymerization with N-alkylated carbazoles significantly increases the conductivity of the polymer film and facilitates rapid charge transport at the interface between the polymer electrode and the electrolyte. The length of the alkyl substituents also plays a crucial role in this improvement. Electrochemical analysis showed a reduction in charge transport resistance from 3.31 Ω·cm² for PEDOT to 2.26 Ω·cm² for the PEDOT:poly(N-octylcarbazole) copolymer, which is almost half the resistance of a platinum-based counter electrode (4.12 Ω·cm²). Photovoltaic measurements showed that the solar cell with the PEDOT:poly(N-octylcarbazole) counter electrode achieved an efficiency of 8.88%, outperforming both PEDOT (7.90%) and platinum-based devices (7.57%). Full article

In this study, we synthesized a ternary transition metal sulfide, Zn_0.76Co_0.24S (ZCS-CE), using a one-step solvothermal method and explored its potential as a Pt-free counter electrode for dye-sensitized solar cells (DSSCs). Comprehensive investigations were conducted to characterize the structural, morphological, compositional, and electronic properties of the ZCS-CE electrode. These analyses utilized a range of techniques, including X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The electrocatalytic performance of ZCS-CE for the reduction of I₃⁻ species in a symmetrical cell configuration was evaluated through electrochemical impedance spectroscopy and cyclic voltammetry. Our findings reveal that ZCS-CE displayed superior electrocatalytic activity and stability when compared to platinum in I⁻/I₃⁻ electrolyte systems. Furthermore, ZCS-CE-based DSSCs achieved power conversion efficiencies on par with their Pt-based counterparts. Additionally, we expanded the applicability of this material by successfully powering an electrochromic cell with ZCS-CE-based DSSCs. This work underscores the versatility of ZCS-CE and establishes it as an economically viable and environmentally friendly alternative to Pt-based counter electrodes in DSSCs and other applications requiring outstanding electrocatalytic performance. Full article

Two-dimensional Cu₂FeSnS₄ (CFTS) nanosheets with exposed high-energy facets (111) have been synthesized by a facile, scalable, and cost-effective one-pot heating process. The CFTS phase formation is confirmed by both X-ray diffraction and Raman spectroscopy. The formation mechanism of exposed high-energy facet CFTS growth is proposed and its electrochemical and photoelectrochemical properties are investigated in detail to reveal the origin of the anisotropic effect of the high-energy facets. Dye-sensitized solar cells (DSSC) achieve a favorable power conversion efficiency of 5.92% when employing CFTS thin film as a counter electrode, suggesting its potential as a cost-effective substitute for Pt in DSSCs. Full article

The counter electrode (CE) is an important and vital part of dye-sensitized solar cells (DSSCs). Pt CEs show high-performance in DSSCs using iodide-based electrolytes. However, the high cost of Pt CEs restricts their large-scale application in DSSCs and the development of Pt-free CE is expected. Here, α-Fe₂O₃/reduced graphene oxide (α-Fe₂O₃/RGO) composites are prepared as the Pt-free CE materials for DSSCs. A simple hydrothermal technique was used to disseminate the α-Fe₂O₃ solid nanoparticles uniformly throughout the RGO surface. The presence of the α-Fe₂O₃ nanoparticles increases the specific surface area of RGO and allows the composites to be porous, which improves the diffusion of liquid electrolyte into the CE material. Then, the electrocatalytic properties of CEs with α-Fe₂O₃/RGO, α-Fe₂O₃, RGO, and Pt materials are compared. The α-Fe₂O₃/RGO CE has a similar electrocatalytic performance to Pt CE, which is superior to those of the pure α-Fe₂O₃ and RGO CEs. After being fabricated as DSSCs, the current–voltage measurements reveal that the DSSC based on α-Fe₂O₃/RGO CE has a power conversion efficiency (PCE) of 6.12%, which is 88% that of Pt CE and much higher than that of pure α-Fe₂O₃ and pure RGO CEs. All the results show that this work describes a promising material for cost-effective, Pt-free CEs for DSSCs. Full article

Miniaturization and wireless continuous glucose monitoring are key factors for the successful management of diabetes. Electrochemical sensors are very versatile and can be easily miniaturized for wireless glucose monitoring. The authors report a microneedle-based enzyme-free electrochemical wireless sensor for painless and continuous glucose monitoring. The microneedles (MNs) fabricated consist of a 3 × 5 sharp and stainless-steel electrode array configuration. Each MN in the 3 × 5 array has 575 µm × 150 µm in height and width, respectively. A glucose-catalyzing layer, porous platinum black, was electrochemically deposited on the tips of the MNs by applying a fixed cathodic current of 2.5 mA cm⁻² for a period of 200 s. For the non-interference glucose sensing, the platinum (Pt)-black-coated MN was carefully packaged into a biocompatible ionomer, nafion. The surface morphologies of the bare and modified MNs were studied using field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray analysis (EDX). The wireless glucose sensor displayed a broad linear range of glucose (1→30 mM), a good sensitivity and higher detection limit of 145.33 μA mM⁻¹ cm⁻² and 480 μM, respectively, with bare AuMN as a counter electrode. However, the wireless device showed an improved sensitivity and enhanced detection limit of 445.75, 165.83 μA mM⁻¹ cm⁻² and 268 μM, respectively, with the Pt-black-modified MN as a counter electrode. The sensor also exhibited a very good response time (2 s) and a limited interference effect on the detection of glucose in the presence of other electroactive oxidizing species, indicating a very fast and interference-free chronoamperometric response. Full article

For large-scale applications, dye-sensitized solar cells (DSSCs) require the replacement of the scarce platinum (Pt)-based counter electrode (CE) with efficient and cheap alternatives. In this respect, low-cost perovskite oxides (ABO₃) have been introduced as promising additives to composite-based CEs in Pt-free DSSCs. Herein, we synthesized composites from La_0.9Ce_0.1NiO₃ (L) perovskite oxide and functionalized-multiwall-carbon-nanotubes wrapped in selenides derived from metal-organic-frameworks (f-MWCNT-ZnSe-CoSe₂, “F”). L and F were then mixed with carbon black (CB) in different mass ratios to prepare L@CB, F@CB, and L@F@CB composites. The electrochemical analysis revealed that the L@F@CB composite with a mass ratio of 1.5:3:1.5 exhibits better electrocatalytic activity than Pt. In addition, the related DSSC reached a better PCE of 7.49% compared to its Pt-based counterpart (7.09%). This improved performance is the result of the increase in the oxygen vacancy by L due to the replacement of La with Ce in its structure, leading to more active sites in the L@F@CB composites. Moreover, the F@CB composite favors the contribution to the high electrical conductivity of the hybrid carbon nanotube–carbon black, which also offers good stability to the L@F@CB CE by not showing any obvious change in morphology and peak-to-peak separation even after 100 cyclic voltammetry cycles. Consequently, the corresponding L@F@CB-based device achieved enhanced stability. Our work demonstrates that L@F@CB composites with a low cost are excellent alternatives to Pt CE in DSSCs. Full article

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm⁻²) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years. Full article

To satisfy the high requirement of catalytic activity for efficient dye-sensitized solar cells (DSSCs), a novel nanoporous NiS film with inverse opal structure and outstanding electrocatalytic properties was prepared by a facile template-assisted electrodeposition method. The inverse opal structure makes the film have a larger specific surface area and more catalytic sites, thereby result to a higher electrocatalytic activity. Compared with the flat NiS/FTO electrode, this kind of nanoporous NiS film with inverse opal structure has higher catalytic activity and can be used as a cheap and efficient Pt-free electrode to replace the traditional Pt/FTO electrode. It is of great significance to reduce the cost and promote the wide application of DSSCs. This study opens up a new experimental exploration for further improving the catalytic activity of NiS electrode and the according photovoltaic efficiency of DSSCs. The template-assisted electrodeposition method proposed in this work provides a facile method for morphology control and an easy to be realized way to optimize the catalytic performance of the metal sulfides counter electrode. Full article

SnO₂-decorated graphene oxide (SnO₂/GO) was synthesized by the modified Hummers’s method, followed by a chemical incorporation of SnO₂ nanoparticles. Then, the nanocomposite was used as anon-precious counter electrode in a dye-sensitized solar cell (DSSC). Although GO has a relatively poor electrical conductivity depending essentially on the extent of the graphite oxidation, presence of SnO₂ enhanced its structural and electrochemical properties. The Pt-free counter electrode exhibited a distinct catalytic activity toward iodine reduction and a low resistance to electron transfer. Moreover, the decorated GO provided extra active sites for reducing I₃⁻ at the interface of the CE/electrolyte. In addition, the similarity of the dopant in the GO film and the fluorine-doped tin oxide (FTO) substrate promoted a strong assimilation between them. Therefore, SnO₂-decorated GO, as a counter electrode, revealed an enhanced photon to electron conversion efficiency of 4.57%. Consequently, the prepared SnO₂/GO can be sorted as an auspicious counter electrode for DSSCs. Full article

Pt as a chemical inert metal has been widely applied as the counter electrode in various electrochemical measurements. However, it can also be dissolved and redeposit to the working electrode under certain electrochemical circumstances. Herein we demonstrated a cyclic voltammetry (CV) cycling method to synthesize a catalyst comprising inserted Pt nanoparticles into MoS₂ nanoflake stack structures on stainless steel mesh (SSM). The binder-free composite structure exhibits significantly enhanced hydrogen evolution reaction (HER) catalytic activity with an overpotentials of 87 mV at 10 mA cm⁻². The deposited Pt nanoparticles significantly enhance the catalytic activity through changing the structure of MoS₂ and increasing the amount of active sites. This work provides a new way forward for rational design of the nano-electrocatalysts. Full article

The production of hydrogen by water splitting has been a very attractive idea for several decades. However, the energy consumption that is necessary for water oxidation is too high for practical applications. On the contrary, the oxidation of organics is a much easier and less energy-demanding process. In addition, it may be used to consume organic wastes with a double environmental benefit: renewable energy production with environmental remediation. The oxidation of organics in a photoelectrochemical cell, which in that case is also referenced as a photocatalytic fuel cell, has the additional advantage of providing an alternative route for solar energy conversion. With this in mind, the present work describes a realistic choice of materials for the Pt-free photoelectrochemical production of hydrogen, by employing ethanol as a model organic fuel. The photoanode was made of a combination of titania with cadmium sulfide as the photosensitizer in order to enhance visible light absorbance. The cathode electrode was a simple carbon paper. Thus, it is shown that substantial hydrogen can be produced without electrocatalysts by simply exploiting carbon electrodes. Even though an ion transfer membrane was used in order to allow for an oxygen-free cathode environment, the electrolyte was the same in both the anode and cathode compartments. An alkaline electrolyte has been used to allow high hydroxyl concentration, thus facilitating organic fuel (photocatalytic) oxidation. Hydrogen production was then obtained by water reduction at the cathode (counter) electrode. Full article

Platinum-free counter electrodes (CE) were developed for use in efficient and cost-effective energy conversion devices, such as dye-sensitized solar cells (DSSCs). Electrochemical deposition of CoS₂ on fluorine-doped tin oxide (FTO) formed a hierarchical sheet-like structured CoS₂ thin film. This film was engaged as a cost-effective platinum-free and high-efficiency CE for DSSCs. High stability was achieved using a phthaloychitosan-based gel-polymer electrolyte as the redox electrolyte. The electrocatalytic performance of the sheet-like CoS₂ film was analyzed by electrochemical impedance spectroscopy and cyclic voltammetry. The film displayed improved electrocatalytic behavior that can be credited to a low charge-transfer resistance at the CE/electrolyte boundary and improved exchange between triiodide and iodide ions. The fabricated DSSCs with a phthaloychitosan-based gel-polymer electrolyte and sheet-like CoS₂ CE had a power conversion efficiency (PCE, η) of 7.29% with a fill factor (FF) of 0.64, J_sc of 17.51 mA/cm², and a V_oc of 0.65 V, which was analogous to that of Pt CE (η = 7.82%). The high PCE of the sheet-like CoS₂ CE arises from the enhanced FF and J_sc, which can be attributed to the abundant active electrocatalytic sites and enhanced interfacial charge-transfer by the well-organized surface structure. Full article

Copper oxide (CuO) and CuO/graphene nanostructured thin films were used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). CuO and CuO/graphene pastes were prepared and coated on fluorine-doped tin oxide (FTO) glass substrates using a doctor-blade coating method. The substrates were then sintered at 350 °C for 30 min to form CuO and CuO/graphene nanostructures. The material properties of the CuO and CuO/graphene CEs were analyzed using a scanning electron microscope, transmission electron microscope, energy-dispersive spectrometer, thermogravimetric analysis instrument, X-ray diffractometer, Raman spectroscopy, X-ray photoelectron spectrometer, ultraviolet-visible spectrophotometer, and cyclic voltammetry instrument. The CuO and CuO/graphene CEs were used to fabricate DSSCs, and the device characteristics were analyzed using current density–voltage, incident photo-to-current conversion efficiency, and electrochemical impedance spectroscopy measurements. The results showed that when CuO and CuO/graphene were used as the CEs, the device conversion efficiencies were 2.73% and 3.40%, respectively. CuO is a favorable replacement for expensive platinum (Pt) because it features a simple fabrication process and is inexpensive and abundant. Furthermore, graphene, which exhibits high carrier mobility, may be added to enhance the electrical and catalytic abilities of CuO/graphene CEs. This is the first study to examine the use of CuO and CuO/graphene for developing Pt-free CEs in DSSCs. Full article

Graphene has been envisaged as a highly promising material for various field emission devices, supercapacitors, photocatalysts, sensors, electroanalytical systems, fuel cells and photovoltaics. The main goal of our work is to develop new Pt and transparent conductive oxide (TCO) free graphene based counter electrodes (CEs) for dye sensitized solar cells (DSSCs). We have prepared new composites which are based on graphene nano-platelets (GNPs) and conductive polymers such as poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Films of these composites were deposited on non-conductive pristine glass substrates and used as CEs for DSSCs which were fabricated by the “open cell” approach. The electrical conductivity studies have clearly demonstrated that the addition of GNPs into PEDOT:PSS films resulted in a significant increase of the electrical conductivity of the composites. The highest solar energy conversion efficiency was achieved for CEs comprising of GNPs with the highest conductivity (190 S/cm) and n-Methyl-2-pyrrolidone (NMP) treated PEDOT:PSS in a composite film. The performance of this cell (4.29% efficiency) compares very favorably to a DSSC with a standard commercially available Pt and TCO based CE (4.72% efficiency in the same type of open DSSC) and is a promising replacement material for the conventional Pt and TCO based CE in DSSCs. Full article