Oxide Counter Electrode Research Articles

Dual-Band Electrochromic Devices Utilizing Niobium Oxide Nanocrystals.

In this study, we realize functioning electrochromic devices based on colloidal niobium oxide nanocrystals, which show dual-band electrochromic behavior, with spectral selectivity between near-infrared and visible wavelengths. Minimally coloring vanadium oxide counter electrodes allow for full electrochromic devices that embody the dual-band electrochromic behavior of the niobium oxide component. The devices are fabricated using solution processing on both glass and flexible substrates, demonstrating that our platform has potential for the development of low-cost dual-band electrochromic devices for dynamic solar control in a variety of form factors and applications.

Construction of Low Cost, and Platinum‐Free Counter Electrode for Dye‐Sensitized Solar Cells

AbstractRecently, design and fabrication of platinum free counter electrodes have received enormous attention of the scientific community. In this work, we have fabricated manganese dioxide/reduced graphene oxide (MnO2@Gr) counter electrode based DSSCs. Hydrothermal method was utilized for the synthesis of MnO2@Gr. Further, X‐ray diffraction technique (XRD), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy (XPS) were employed as physiochemical characterization technique. Surface structural investigations showed that MnO2 has rods like surface morphology which are attached with Gr. The fabricated DSSCs demonstrated good open circuit voltage (Voc) and reasonable efficiency of 0.72 V and 5.87 %, respectively.

Electrochemical evaluations of reduced graphene oxide for efficient counter electrode in dye-sensitized solar cell

The design and development of an alternative counter electrode (CE) using graphene-based low-cost material for the dye-sensitized solar cell (DSSC) is the major motivation of the current research to replace the traditional platinum counter electrode. Herein, we prepared reduced graphene oxide (rGO) and investigated it for an efficient CE in DSSC. The structural and morphological properties of rGO are analyzed using FESEM, TEM and Raman techniques. The performance of I3- reduction on the CE is characterized by the EIS Nyquist plot, cyclic voltammetry, and the Tafel curve. The measured electrochemical results suggested that rGO CE has a lower charge transfer resistance (Rct), higher cathodic current density (Jrd), and higher Tafel slope as compared to graphene oxide (GO) CE, revealing that rGO CE has good catalytic activity towards the I3- reduction.

Tetrachloroethane (TeCA) removal through sequential graphite-mixed metal oxide electrodes in a bioelectrochemical reactor

Electro-bioremediation offers a promising approach for eliminating persistent pollutants from groundwater since allows the stimulation of biological dechlorinating activity, utilizing renewable electricity for process operation and avoiding the injection of chemicals into aquifers. In this study, a two-chamber microbial electrolysis cell has been utilized to achieve both reductive and oxidative degradation of tetrachloroethane (TeCA). By polarizing the graphite granules cathodic chamber at −650 mV vs the standard hydrogen electrode and employing a mixed metal oxide (MMO) counter electrode for oxygen production, the reductive and oxidative environment necessary for TeCA removal has been established. Continuous experiments were conducted using two feeding solutions: an optimized mineral medium for dechlorinating microorganisms, and synthetic groundwater containing sulphate and nitrate anions to investigate potential side reactions. The bioelectrochemical process efficiently reduced TeCA to a mixture of trans-dichloroethylene, vinyl chloride, and ethylene, which were subsequently oxidized in the anodic chamber with removal efficiencies of 37 ± 2%, 100 ± 4%, and 100 ± 5%, respectively. The introduction of synthetic groundwater with nitrate and sulphate stimulated reductions in these ions in the cathodic chamber, leading to a 17% decrease in the reductive dechlorination rate and the appearance of other chlorinated by-products, including cis-dichloroethylene and 1,2-dichloroethane (1,2-DCA), in the cathode effluent. Notably, despite the lower reductive dechlorination rate during synthetic groundwater operation, aerobic dechlorinating microorganisms within the anodic chamber completely removed VC and 1,2-DCA. This study represents the first demonstration of a sequential reductive and oxidative bioelectrochemical process for TeCA mineralization in a synthetic solution simulating contaminated groundwater.

Polymer-free gel electrolyte and its application in TiO2-based electrochromic devices

Electrochromic devices based on polymer-free gel electrolytes (PFGEs) offer several advantages over polymer electrolytes. The preparation and characterization of a novel fumed silica-based PFGE and its applications in TiO2 electrochromic devices (ECD) were the main aims of the present study. First, a series of liquid electrolytes were prepared by mixing lithium chloride (LiCl) and ethylene Glycol (EG) with different molar ratios and their ionic conductivities were measured to get an idea about the highest ionic conductivity composition. The total oxygen atoms of EG to lithium ions of LiCl molar ratio (O:Li+) was altered from 5:1 to 80:1. The highest ionic conductivity was observed for 15: 1 molar ratio with the value being the 1.28 × 10− 2 S cm− 1. This optimized composition was selected for preparing PFGE. In order to prepare PFGE, 10 wt% of fumed silica from the total weight of EG and LiCl were added to the optimized liquid electrolyte EG/LiCl as the polymer-free gelling agent. The maximum ionic conductivity was found in O:Li = 10: 1, with the value being 8.94 × 10− 3 S cm− 1. ECDs were prepared by sandwiching this PFGE between TiO2 electrochromic electrode and fluorine-doped tin oxide (FTO) counter-electrode with the configuration of FTO/TiO2/PFGE/FTO. Notable electrochromic properties of TiO2-coated FTO with higher optical modulation of 64% at 700 nm and 33% at 550 nm by applying 4.2 V and a switching speed of Tbleaching= 42.5 s and Tcoloring= 16.7 s were observed.

Improvement of the performance of dye-sensitized solar cells employing NickelPalladium alloy-reduced graphene oxide counter electrode: Influence of palladium content

In this work, NickelPalladium-reduced graphene oxide (NiPd-rGO) films have been prepared via liquid phase deposition technique and used as free-platinum (Pt) counter electrode for dye-sensitized solar cell (DSSC). The effect of Pd content in term of various Ni:Pd ratios on the properties such as structure, optical transmission, surface morphology and elemental compositions have been studied. The morphology of NiPd-rGO sample is in the form of crumpled vertical folds in layers and white strips. The influence of Pd content on photovoltaic parameters of the device has also been investigated. The performance parameters were significantly influenced by the Pd content. The device using NiPd-rGO counter electrode prepared at Ni:Pd ratio of 20:2 demonstrated the highest PCE of 3.09%. This is due to the device owns the highest charge recombination resistance (Rrec) and shortest carrier transport time (τ). The efficiency has been improved at the optimum content of Pd. The finding from this work implies that NiPd-rGO is able to substitute Pt as counter electrode in DSSC due to its efficiency is comparable to that of the device employing Pt counter electrode.

Dye-sensitized solar cell using nickel sulfide-reduced graphene oxide counter electrode: Effect of sulphur content

The influence on sulphur content in term of thiourea (TU) concentration on the properties of nickel sulphide (NiS)-reduced graphene oxide (rGO) has been reported in this paper. The effect of sulphur content on the performance of dye-sensitized solar cell (DSSC) using NiS-rGO counter electrode (CE) has also been investigated. The source of sulphur is TU. The sample has been prepared via modified Hummers’s method assisted with spin coating technique. The cell using NiS-rGO CE prepared with 1.20 M TU yielded the highest power conversion efficiency (η) of 1.42%. This is due to this cell has the lowest series resistance (Rb) and charge transfer resistance at the interface of NiS-rGO CE/electrolyte (Rct) with the value of 0.44 and 4.09 Ω, respectively. It is also due to the sample with 1.20 M TU owns the highest reduction current (J). The finding of this work reveals that NiS-rGO is able to substitute platinum as CE for DSSC.

Construction of Ni doped MoO3 nanostructures and their application as counter electrode in dye-sensitized solar cells

In this research, we propose to develop a sustainable, affordable and non-toxic material in dye sensitized solar cells for counter-electrodes (DSSCs). As a low-cost equivalent to platinum, we describe a facile aqueous hydrothermal solution-processed nickel (Ni) doped molybdenum oxide (MoO3) counter electrode. The Ni concentration in to MoO3 was varied from 0 to 10 mol.%. The effect of Ni dopant on the microstructure, particle size and optical behavior of MoO3 was systematically investigated. The 10% Ni incorporated MoO3 showed high absorption in the visible light with optical band gap energy is close to 2.98 eV. The optimized CE with 10% Ni-MoO3 (NMO10) showed outstanding photo conversion efficiency (8.39%), long term stability and higher electrocatalytic activity. The order of the photovoltaic and electrocatalytic properties are NMO10 > NMO5 > NMO2 > MoO3. In addition, the Rct value of this electrode is lower and shows a lower resistance to charge transfer and higher electrocatalytic activity. The improved photoconversion mechanism of Ni in to MoO3 was also described in detail.

Fabrication and performance evaluation of dye-sensitized solar cell integrated with natural dye from Strobilanthes cusia under different counter-electrode materials

The ruthenium-based dye and platinum (pt) are the most common materials used as photosensitizer and counter electrode (CE), respectively, in the production of the dye-sensitized solar cell (DSSC), the third generation of photovoltaic technologies. However, their expensive cost, the complexity and toxicity of ruthenium dye, and the scarcity of pt’s sources preclude their use in the DSSC. Thus, this has sparked much interest in integrating natural dyes such as chlorophylls, the predominant pigments found in nature and responsible for photosynthesis, and exploring platinum-free CE in developing DSSC. This research investigated the natural dye from Strobilanthes cusia (SC) and evaluated the performance output under the three various counter electrode materials: a. fluorine-doped tin oxide (FTO) CE; b. graphite/FTO CE; and c. pt/FTO CE. Hence, from this study’s results, it was found that the SC dye is primarily composed of Chl-a with 64.5345 ± 0.4226 μg/ml followed by Chl-b with 41.4341 ± 0.2636 μg/ml. While in the photovoltaic performance of the SC dye-based DSSC the graphite/FTO CE showed higher photoelectric output having an open-circuit voltage (Voc) of 306.35 mV, short circuit current (Isc) of 15.55 μA, ff = 0.462, maximum power (PMAX) of 0.734 μW/cm2 and an efficiency (η) of 0.0385%. For the pt/FTO CE, the values obtained were Voc = 283.39 mV, Isc = 9.43 μA, ff = 0.252, PMAX = 0.225 μW/cm2 and η = 0.0118%, and last, for FTO CE, Voc = 192.62 mV, Isc = 2.94 μA, ff = 0.203, PMAX = 0.0128 μW/cm2, and η = 0.00067%. It can be concluded that graphite presents feasible potential as an alternative to platinum due to its affordable cost and performance output.

Towards superior nickel oxide electrochromic films using Si and Li co-doping and rapid thermal annealing

Herein, we firstly report a novel technical routine to improve the electrochromic (EC) performance of frequently-used nickel oxide counter-electrode films by RF magnetron sputtering using a Si and Li co-doping oxide target in Ar atmosphere and subsequently rapid thermal annealing (RTA) at 400 °C in air. The effects of co-doping and RTA treatment on the phase structure, microstructure, chemical states of Ni element, and EC properties of films were comprehensively investigated using X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and electrochemical analysis. Comparing with the undoped and the as-deposited films, it is found that the mutual effects of Si and Li co-doping and RTA treatment can promote a preferential growth in (111) direction of nickel oxide, enhance the relative atomic concentration of Ni3+ to 60% in the total Ni element, and help to form a smooth and compact structure with uniformly distributed fine pinholes. The doped and annealed film behaves with the highest bleached transmittance of 93.3% (at 550 nm), largest optical modulation of 37.0% (at 550 nm), biggest charge capacity of 14.8 mC•cm−2, best electrochemical stability to bear more than 100 cycles, and rapid bleaching and coloring response times of 2.4 and 8.8 s. These superior performances make this kind of material promising for future application in high quality EC devices.

Graphene nanoparticles-decorated silicon nanowires with tungsten oxide counter electrode for quasi-solid state hybrid solar cells

Visible light harvesting IL-GNP co-sensitized SiNW yield 7.93% efficiency for the solar cell. The I2,I- gel with SiO2 nanoparticles efficiently scavenges holes from IL-GNP/SiNW heterojunction and restricts photoanode degradation.

In situ synthesis of ZnFe2O4 rough nanospheres on carbon nanofibers as an efficient titanium mesh substrate counter electrode for triiodide reduction in dye-sensitized solar cells

There is no doubt that counter electrode (CE) plays a vital role in dye-sensitized solar cells (DSSCs). Herein, Zinc Ferrite/carbon nanofibers (ZnFe2O4/CNFs) composite is successfully fabricated by electrospinning and hydrothermal method and coated on titanium (Ti) mesh as an efficient CE material, which is further applied to DSSCs. The Ti mesh has been done as conductive substrate to make the DSSCs have smaller transmission resistance, great stability and sustainable utilization. Via repeated measurements, the ZnFe2O4/CNFs CE which is prepared on Ti mesh exhibits good power conversion efficiency (PCE) of 9.05%, which is higher than commercial Platinum (Pt) fluorine-doped tin oxide (FTO) CE (7.21%) and CNFs Ti mesh CE (7.80%) under the same conditions. Most interestingly, the CNFs CE that prepared on Ti mesh has higher PCE than Pt CE, this is mainly due to the use of Ti mesh which is more conducive to the interface transport of iodine ion and electron transfer rate. All of these results indicate that ZnFe2O4/CNFs composite Ti mesh CE has high electrochemical performance and can be favorable for low-cost efficient DSSCs application.

Efficiency Studies of Galinsoga Parviflora Pigments as a Sensitizer in Pt Free Graphene Oxide/Nickel Oxide Counter Electrode: Dye Sensitized Solar Cell Applications

An easily available Galinsoga Parviflora (GP) natural dye has been used as natural sensitizers for dye sensitized solar cell (DSSC). Graphene oxide (GO) is one of the most efficient materials for solar cells, supercapacitor and sensing applications because of its unique properties. It is prepared from natural graphite flakes by modified Hummer’s method. Graphene oxide/nickel oxide (GO/NiO) nanocomposites are prepared by chemical precipitation method. The different concentrations of nickel oxide nanoparticles (5:1, 5:2 and 5:3) are embellished on the GO surface. The synthesis of these nanocomposites are confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). The XRD results confirmed that the nickel oxide nanoparticles are coated on the graphene oxide surface and the crystallite size of GO/NiO (5:1, 5:2 and 5:3) nanocomposites are found to be around 19 nm, 21.3 nm and 23 nm respectively. The electrochemical activity of the prepared nanocomposites is investigated by cyclic voltammetry (CV) technique. The power conversion efficiency is measured using a light source simulated with an intensity of 100 mW/cm2. The conversion efficiency of prepared sandwich type dye sensitized solar cell (5:1, 5:2 and 5:3) is 0.9%, 1.3% and 1.65% respectively.

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.

Nickel doped molybdenum oxide thin film counter electrodes as a low-cost replacement for platinum in dye sensitized solar cells

Replacement of expensive platinum counter electrodes has been primarily focusing research on Dye-Sensitized Solar Cells. Here, we present a facile solution-processed thin-film nickel doped molybdenum oxide counter electrode as a cheap alternative of Platinum. The most motivation of doping nickel in molybdenum oxide was to explore the synergic effect produced due to hypo-hyper electronic d orbital coupling between the pair. These results show the shift of valence band energy level upwards to properly align with electrolyte redox potential for facilitating hole transport. We found that optimized 10 mol. % Ni doping yielded the maximum efficiency of the fabricated solar cells.

Water-dispersible polyaniline/graphene oxide counter electrodes for dye-sensitized solar cells: Influence of synthesis route on the device performance

The fabrication of efficient and platinum-free counter electrodes (CE) is a highlighted topic for the development of advanced dye-sensitized solar cells (DSSCs). Here, we developed water-dispersible polyaniline/graphene oxide (PANI-GO)-based CEs, which can be straightforwardly prepared by deposition of the nanocomposite dispersion onto FTO substrate. The water-dispersibility properties of PANI-GO allow the formation of smooth films without organic solvents making it a promising material for high-scalable, reduced cost and ‘greener’ fabrication of energy conversion-storage devices. Aqueous dispersions of PANI-GO nanocomposites were prepared by two different routes: physical mixture of PANI and GO, and in situ polymerization of aniline in GO aqueous dispersion. DSSC assembled with emeraldine salt polyaniline (PANI-ES)-based CE generated current density (Jsc) of 12.37 mA/cm2 and power conversion efficiency (PCE) of 5.09%, which was comparable to the device prepared with Pt-based CE (PCE of 5.15%). The addition of GO is found to increase the Jsc to 12.91 mA/cm2 and the fill factor to 67% in CE containing 0.45 wt% of GO (in respect to aniline during synthesis) where the PCE is boosted to 6.12%, which is about 20% higher than Pt-based CE. The investigation of both morphological features and spectroscopic properties showed that PANI-GO nanocomposites prepared by in situ route have dissimilar protonation and oxidation states when compared with those prepared by physical mixture route. These results give insights into the role of GO in tuning PANI chemical and physical properties. Also offers a simpler and more efficient methodology for the synthesis of new CEs for DSSCs.

Integrated Devices for Photoelectrochemical Water Splitting Using Adapted Silicon Based Multi-Junction Solar Cells Protected by ALD TiO2 Coatings

Abstract In this study, we present different silicon based integrated devices for photoelectrochemical water splitting, which provide enough photovoltage to drive the reaction without an external bias. Thin films of titanium dioxide, prepared by atomic layer deposition (ALD), are applied as a surface passivation and corrosion protection. The interfaces between the multi-junction cells and the protective coating were optimized individually by etching techniques and finding optimal parameters for the ALD process. The energy band alignment of the systems was studied by X-ray photoelectron spectroscopy (XPS). Electrochemically deposited platinum particles were used to reduce the HER overpotential. The prepared systems were tested in a three-electrode arrangement under AM 1.5 illumination in 0.1 M KOH. In final tests the efficiency and stability of the prepared devices were tested in a two-electrode arrangement in dependence of the pH value with a ruthenium-iridium oxide counter electrode. For the tandem-junction device solar to hydrogen efficiencies (STH) up to 1.8% were reached, and the triple-junction device showed a maximum efficiency of 4.4%.

Improving Performance of Nonfullerene Organic Solar Cells over 13% by Employing Silver Nanowires-Doped PEDOT:PSS Composite Interface.

Ag nanowires (NWs)/PEDOT:PSS composite was prepared by a facile solution-processing method and employed as anode interface in nonfullerene organic solar cells (OSCs). In the presence of a Ag NWs (5%, v/v%)/PEDOT:PSS interfacial layer, a high-power conversion efficiency up to 13.53% was achieved based on a PBDB-T-2Cl:IT-4F photoactive layer system, much higher than the efficiency of the controlled counterpart device with pristine PEDOT:PSS as anode modifier. Simultaneous enhancements in short-circuit current and fill factor were observed, in comparison to the case of the pristine PEDOT:PSS interface, due to the improved electrical conductivity of Ag NWs/PEDOT:PSS composites accompanied by the increased work function for a better matching with the indium tin oxide counter electrode, which facilitated increased charge transferand reduced charge recombination at the anode/photoactive interface for improved device performance. The results clearly revealed that the Ag NWs/PEDOT:PSS composite interface is beneficial to improve the charge extraction and favor the realization of highly efficient nonfullerene OSCs.

On-Surface Self-Assembly of Stimuli-Responsive Metallo-Organic Films: Automated Ultrasonic Spray-Coating and Electrochromic Devices.

We demonstrate the on-surface formation of homogeneous and uniform electrochromic films via ultrasonic spray coating. This fully automated process is capable of fabricating metallo-organic films on transparent conducting oxides (TCOs) on glass or flexible poly(ethylene terephthalate) (PET) with surface areas of up to 36 cm2 and film thicknesses of half a micron. The assembly process involves alternatingly spray-coating dilute solutions of structurally well-defined iron polypyridyl ([Fe(mbpy-py)3]2+) complexes and bis(benzonitrile)palladium dichloride (Pd(PhCN)2Cl2) onto conductive substrates, where the latter palladium salt was used as the inorganic cross-linker. The on-surface self-assembled three-dimensional networks are intensely colored and were subsequently integrated into laminated electrochromic devices (ECDs) containing a lithium-based gel electrolyte. The ECDs retain their intense color in the ground state, having a Δ Tmax of 40-49% at λmax ≈ 600 nm, and can be operated for up to 1500 redox cycles. The fluorine-doped tin oxide counter electrode coated with poly(3,4-ethylene-dioxythiophene)polystyrene sulfonate (PEDOT:PSS) as a charge-storage layer resulted in these stable devices. A significant decrease in the potential window of Δ E ≈ 2.5 V was achieved by using a metal grid on PET as the counter electrode. The operation of the electrochromic films is diffusion-controlled, and the diffusion coefficients ( Df) reflect their molecular densities. During these studies, we found that ClO4- is a suitable counterion of the lithium-based electrolytes for optimal ECD performance.

Scalable screen-printing manufacturing process for graphene oxide platinum free alternative counter electrodes in efficient dye sensitized solar cells

The graphene oxide paste (GO) was prepared by mixing α-terpineol and ethyl cellulose, and GO films was prepared by screen printing on fluorine doped Tin oxide (FTO) glass substrates to validate as an alternative counter electrode material to platinum in dye sensitized solar cells (DSSC). The graphene oxide films were characterised by X-Ray Diffraction, Scanning Electron Microscopy, Raman spectroscopy and the catalytic properties of films were being investigated by cyclic voltammetry and electrochemical Impedance measurements. The DSSC fabricated by coupling TiO2 films soaked in N719 dye with GO as counter electrode exhibited photoconversion efficiency of 5.58% under standard one Sun illumination, whereas platinum based device showed photoconversion efficiency of 7.57%. The present study suggests that graphene oxide counter electrodes can be considered as a promising alternative to platinum, with further optimisation, which clearly has advantages in terms of its abundance and low cost processing towards industrial prospects.