Counter Electrode Material Research Articles

Unveiling the Potential of MnxCo3–xS4 Electrocatalyst in Triiodide Reduction for Dye-sensitized Solar Cells

The development of a low-cost and high-efficiency Pt-free counter electrode is an important goal to improve the performance of dye-sensitized solar cells. In this study, we successfully synthesized a MnxCo3-xS4-based counter electrode by a facile solvothermal synthesis technique. The electrocatalyst was directly deposited on a fluorine doped titanium oxide (FTO) coated glass substrate. Various characterization techniques such as Xray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were employed to analyze the obtained MnxCo3-xS4 counter electrode material. The photovoltaic measurements performed on the dye-sensitized solar cells showed a remarkable improvement in energy conversion efficiency with the MnxCo3-xS4 counter electrode (8.60 %) compared to the conventional Pt (8.11 %). Moreover, the MnxCo3-xS4counter electrode exhibited excellent stability, further highlighting its potential as an efficient and durable alternative to Pt in dye-sensitized solar cells. Overall, our results contribute to the further development of Pt-free counter electrode materials for sustainable solar energy applications.

Nitrogen-doped reduced graphene oxide enfolded zinc cobaltite micro flowers as efficient triiodide reduction for a platinum-free counter electrode in dye-sensitized solar cell applications

Diverse varieties of organic and inorganic materials have been employed as counter electrodes (CEs) in dye-sensitized solar cell applications (DSSCs) to replace platinum (Pt). Interestingly, the influence of N-doped reduced graphene oxide on ZnCo2O4 with high surface area, superior electrical activity, and chemical stability has been addressed in this work. Pure ZnCo2O4 (ZCO), ZnCo2O4/reduced graphene oxide (rGO) (ZCOG), and ZnCo2O4/nitrogen-doped reduced graphene oxide (N-rGO) (ZCONG) had synthesized using a facile hydrothermal technique, and their performance as a CE material in DSSC application was further investigated. The formation of the material free of impurities is depicted by X-Ray Diffraction (XRD) and Raman analysis. The analysis utilizing Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) confirmed the existence of ZnCo2O4 micro flowers made of rods and sheets as well as the thin sheet-like shape of graphene oxide (GO) and N-rGO. The X-ray photoelectron spectroscopy (XPS) analysis technique was employed to determine the chemical composition and purity of the prepared samples. Further, the BET analysis confirms the higher specific surface area (1198.431 m2/g) of the ZCONG sample. The electrochemical property of the coated CEs was investigated using cyclic voltammetry (CV) analysis with the iodine-based electrolyte in a three-electrode system showing superior catalytic properties of the ZCONG CE than the other ZCO and ZCOG CEs. The as-fabricated CEs were utilized to assemble the DSSC device, and the ZCONG CE reached a photovoltaic power conversion efficiency (PCE) of 5.84 ± 0.06%, surpassing ZCO (3.51 ± 0.15 %) and ZCOG (4.81 ± 0.08 %) CEs.

Phosphorus-doped molybdenum disulfide as counter electrode catalyst for efficient bifacial dye-sensitized solar cells

MoS2 is a promising counter electrode material for dye-sensitized solar cell owing to its optical and electrical properties and two-dimensional layered structure. However, it still suffers from minimal conductivity, poor charge transport and less active sites. The present study offers a promising method for enhancing catalytic and fast charge transfer in MoS2 through heteroatom doping of phosphorus. A facile one-step hydrothermal treatment was acquired to do the phosphorus doping. The spin-coated P-doped MoS2 (MSP2) counter electrode (CE) shows a superior power conversion efficiency of 7.93% for front illumination and 5.34% for rear illumination, outperforming Pt-based (7.41% and 5.75%) CE. Thus, phosphorous incorporation increases the number of active sites and improves the catalytic property of the material. The P-doped MoS2 (MSP2) CE film also shows high transmittance, making it a suitable choice for bifacial type of solar cell.

Dialing in the Voltage Window: Reconciling Interfacial Degradation and Cycling Performance Decay with Cation-Disordered Rocksalt Cathodes

Lithium-excess, cation-disordered rocksalt (DRX) materials have received considerable interest as cathode materials for Li-ion batteries, owing to their high specific capacity and compositional flexibility. Despite these advantages, high interfacial reactivity of DRX materials causes extensive oxidative electrolyte degradation at the cathode-electrolyte interface. In addition to consuming electrolyte, this interfacial degradation is likely to lead to a cascade of deleterious effects throughout the cell, as reactive degradation products drive secondary degradation processes like dissolution of transition metals and decomposition of passivating interfacial species. While in-situ gas evolution measurements conducted by differential electrochemical mass spectrometry (DEMS) allow for the observation and quantification of the degradation processes occurring at the DRX surface, the customized cell configuration with which the technique is conducted is not well suited for capturing the performance decay driven by the interfacial degradation. In particular, a large excess of electrolyte and a large Li metal counter-electrode, both of which are necessary features of DEMS cells, serve to mask the deleterious effects of the interfacial degradation on electrochemical performance. In this work, we reconcile the degradation observed by DEMS with performance decay measured by extended cycling experiments in electrolyte-lean full cells. By comparing DRX outgassing and cycling performance in different voltage windows, we demonstrate a positive correlation between the extent of outgassing and the rate of DRX performance decay during cycling. This result provides a crucial link between the degradation measured by techniques like DEMS and the performance decay measured by cycling experiments, and it allows for the fine-tuning of a cycling voltage window which optimizes the tradeoff between initial performance and long-term stability. Furthermore, this work emphasizes the importance of cell design features, like electrolyte volume and counter-electrode material, and their impact on different electrochemical experiments.

Synthesis of nitrogen-doped reduced graphene oxide as counter electrode material for dye-sensitized solar cells

Synthesis of nitrogen-doped reduced graphene oxide as counter electrode material for dye-sensitized solar cells

Structural, electronic and optical properties of chromium carbide (Cr3C) as potential counter electrode material: a first principle study

Transition metal carbides are recently considered to be potential substitutes to platinum counter electrode due to their low cost, high catalytic activity and good thermal stability. In this paper, we investigate the structural, electronics, and optical properties of one of the transition metal carbides (Cr3C). The structural and electronic properties were computed using the first principles approach, a generalized gradient approximation (PBE-GGA) as exchange correlation functional within density functional theory (DFT) was used for the calculations. The optimized lattice parameters of the compound were = 4.525 Ǻ, = 5.186 Ǻ, = 6.659 Ǻ and ∝ = β = γ = 90.00which are in agreement with number of theoretical and experimental results. The calculated band gap and density of state (DOS) of this compound reveals the presence of Valence Band Maximum (VBM) and Conduction Band Minimum (CBM) at different symmetry point with the intersection of several energy bands crossing the Fermi level, this interaction indicate a metallicity nature and may cost the conductive nature of the material to have sufficient electro-catalytic ability for the reduction of I3- ions in counter electrode of DSSCs. The optical properties are calculated from the spectra of dielectric function alongside with the other related optical properties like energy loss function, reflectivity, refractive index, extinction coefficient and conductivity within a continuous energy range of 0 to 16eV. The obtained results of the optical properties of this material show that the materials can be use as possible candidates for counter electrode of DSSC.

An electrolyte-free electrochromic device using aluminum as counter electrode material

In this study, a novel all-solid-state electrochromic device (ECD) free of indium tin oxide (ITO), tungsten(VI) oxide (WO3), and Li+ or any other liquid/gel electrolytes was prepared by a cost-effective and industrially applicable spray coating technique. The device configuration consists of a pre-formed Al-coated glass substrate for use as a counter electrode in the fabrication of an ECD with a glass/Al/Alq3/PEDOT:PSS structure. The fabricated device (2.5 × 4.0 cm2) demonstrated a reversible color change between a light-blue (off) and dark-blue (on) state, with good and homogeneous contrast. The ECD started coloring at − 0.5 V and was completely colored at – 2.0 V, showing various tones of blue according to the applied voltages. The coloration efficiency was 174.62 cm2/C and the cycle stability was achieved at least 150 times.

Exploring a novel counter electrode material (NiO/Co3O4/CuO anchored on rGO) as an efficient replacement for platinum in dye-sensitized solar cells

Solar cells are one of the best-suited devices which can deal with drastic energy demands due to advancements in technology. In this work, Pt-free rGO/NiO/Co3O4/CuO (RNCC) was developed to serve as the counter electrode for dye-sensitized solar cells. RNCC was used with a variety of photoanodes (PA), including TiO2, ZnO, and TiO2/ZnO employing N-719 as the dye matrix and FTO as the substrate. The produced Dye-Sensitized Solar Cells (DSSCs) were tested in terms of their functionality, optical properties and photovoltaic performance. The produced DSSC using RNCC as the counter electrode was fabricated 20 times to ensure its reproducibility and was discovered to have a promising photo conversion efficiency (PCE) of 7.33 % which is 90.13 % of Pt counter electrode (8.3 %) used under the identical conditions. Thus, making the RNCC nanocomposite serve as a virtuous alternative to high-cost Pt as CE thereby accelerating cost-efficient in DSSCs in the future.

Carbon nanotubes/PANI composite as an efficient counter electrode material for dye sensitized solar cell

Counter electrodes of dye sensitized solar cells (DSSCs) mainly employed platinum (Pt) as a catalyst due to high catalytic activity toward triiodide reduction in their operating process. However, using Pt in DSSCs highly increases the cost, which became a challenge for practical applications from their economic feasibility point of view. Therefore, in this work, we have developed a cost-effective material carbon nanotubes (CNTs) to replace expensive Pt. CNTs based DSSC has been considered as a potential candidate for future practical applications. We prepared CNTs/Polyaniline (PANI) composite as a CE material for DSSCs by doctor blade technique. The DSSCs fabricated with CNTs-PANI composite CE show the best power conversion efficiency (PCE) of 6.67%, which is comparable to 7.70% of Pt CE. The modified CNTs-PANI counter electrode exhibited excellent electrocatalytic activity that facilitated higher electron transfer, suppressed charge recombination, enhanced electron life, and faster triiodide reduction are confirmed by several characterisation techniques such as impedance spectroscopy, cyclic voltammetry (CV), and tafel analysis. A comparative study of these electrodes reveal that effective surface roughness plays an essential role in improving the electrochemical properties of the devices.

Phase-Selective Synthesis of Cobalt Sulfide Heterostructure Catalysts as Efficient Counter electrodes in Dye-Sensitized Solar Cells.

Developing a cost-saving, high-efficiency, and simple synthesis of counter electrode (CE) material to replace pricy Pt for dye-sensitized solar cells (DSSCs) has become a research hotspot. Owing to the electronic coupling effects between various components, semiconductor heterostructures can significantly enhance the catalytic performance and endurance of counter electrodes. However, the strategy to controllably synthesize the same element in several phase heterostructures used as the CE in DSSCs is still absent. Here, we fabricate well-defined CoS2/CoS heterostructures and use them as CE catalysts in DSSCs. The as-designed CoS2/CoS heterostructures display high catalytic performance and endurance for the triiodide reduction in DSSCs thanks to the combined and synergistic effects. As a result, a DSSC with CoS2/CoS achieves a high power conversion efficiency of 9.47% under illumination, surpassing that of pristine Pt-based CE (9.20%). Besides, the CoS2/CoS heterostructures possess a quick activity initiation process and extended stability, broadening their potential applications in various areas. Therefore, our proposed synthetic approach could offer new insights for synthesizing functional heterostructure materials with improved catalytic activities in DSSCs.

Electrochemical and power conversion performance of different counter electrode materials for flexible dye-sensitized solar cells.

Carbon dots and copper indium sulfide are promising photovoltaic materials, which have so far been fabricated mainly by chemical deposition methods. In this work, carbon dots (CDs) and copper indium sulfide (CIS) were separately combined with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) for the preparation of stable dispersions. These prepared dispersions were used to produce CIS-PEDOT:PSS and CDs-PEDOT:PSS films using the ultrasonic spray deposition (USD) approach; furthermore, platinum (Pt) electrodes were fabricated and tested for flexible dye sensitized solar cells (FDSSCs). All the fabricated electrodes were utilized as counter electrodes for FDSSCs, and the power conversion efficiency of the FDSSCs reached 4.84% after 100 mW cm-2 AM1.5 white light was used to excite the cells. More investigation reveals that the improvement might be caused by the CDs film's porosity network and its strong connection to the substrate. These factors increase the number of sites available for the effective catalysis of redox couples in the electrolyte and facilitate the movement of charge in the FDSSC. It was also emphasized that the CIS film in the FDSSC device helps to generate a photo-current. In the beginning, this work shows how the USD approach can create CIS-PEDOT:PSS and CDs-PEDOT:PSS films and confirms that a CD based counter electrode film produced using the USD method is an interesting replacement for the Pt CE in FDSSC devices, while the results obtained from CIS-PEDOT:PSS are also comparable with standard Pt CE in FDSSCs.

Unraveling the Enhanced Electrochemical Performances of Nickel Aluminum Sulfide Lattices for Overall Water Splitting and as Counter Electrode Materials for Dye-Sensitized Solar Cells

The development of a high-performance precious metal-free multifunctional electrocatalyst for overall water splitting is a promising sign for future energy research. Here, a new strategy has been followed for the synthesis of novel-structured binary metal chalcogenide electrocatalysts, such as nickel aluminum sulfide (NiAl2S4) or nickel aluminum selenide (NiAl2Se4) spinels. The new chalcogenides, NiAl2S4 or NiAl2Se4, were confirmed by different physicochemical characterizations. Using a 316 stainless steel (SSL) mesh electrode as a three-dimensional conducting substrate, the electrocatalytic overall water splitting reaction was studied. Here, NiAl2S4 spinel outperformed the other metal chalcogenide in terms of electrocatalytic activity and charge transport in the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and overall water splitting in alkaline medium. Moreover, NiAl2S4 spinel provided the finest electrocatalytic efficiencies compared to other benchmark electrocatalysts with minimized overpotentials, such as 47 or 290 mV for HER or OER, respectively, to reach the current density of 20 mA cm–2. In overall water splitting studies, a two-electrode system was formulated to show a very low potential of 1.54 V at a current density of 20 mA cm–2. Further, the prepared NiAl2S4 electrocatalyst-loaded 316 SSL electrode demonstrated excellent durability in HER, OER, and overall water splitting reactions. The obtained Faradaic efficiency was 97%, which is due to the two-dimensional sheet-like morphology of NiAl2S4, enabling a high active surface area for efficient water electrolysis. Furthermore, NiAl2S4 spinel performed well as a counter electrode (CE) material in dye-sensitized solar cells, with an efficiency of 5.02% compared to Pt (5.38%) on the fluorine-doped indium tin oxide electrode.

In Situ Gravimetric Probing of Copper Sulfide Formation on the Counter Electrode for Quantum Dot Sensitized Solar Cells

Copper sulfide is a classical counter electrode (CE) catalytic material for the high catalytic activity of polysulfide in quantum dot-sensitized solar cells (QDSSCs). Actually, copper sulfide is a complicated compound. Different preparation methods will lead to the difference in the morphology and structure of copper sulfide, which has a profound impact on its catalytic activity. However, the formation mechanism and electrochemical properties of copper sulfide are rarely reported in the field of QDSSCs. Herein, we report an approach to obtain a high-stability counter electrode material by the electrochemical synthesis in sodium sulfide solution. The in situ electrochemical quartz crystal microbalance (EQCM) method was also employed to reveal the detailed transformation mechanism of copper vulcanized into copper sulfide during cyclic voltammetry in sodium sulfide solution. According to the calculation results of mpe theory, the formation of copper sulfide is accompanied by side reactions such as the conversion of polysulfide ions and water oxidation. Copper sulfide was proven to be a copper-rich phase by X-ray photoelectron spectroscopy (XPS) and other characterization methods. The photoconversion and stability of QDSSCs were studied using CdSe QD as the sensitizing material. The results show that the performance of copper sulfide prepared by this working method is better than the CE prepared by chemical bath deposition (CBD), and the replicability of photoelectric conversion efficiency (PCE) is better than CBD-CE. This work has theoretical significance to reveal the complex formation mechanism, electrochemical process mechanism, and working mechanism of copper sulfide in QDSSCs.

Hydrothermally grown MoS2-flowers as low cost counter electrode material for dye sensitized solar cell and electrode modifier for electrochemical sensing of 4-chlorophenol

In present scenario, energy crisis and environmental pollution are the two major concerns which need immediate attention. Design and fabrication of bi-functional materials to deal with the above concerns are the major challenges for scientific community. Herein, we reported the bi-functional properties of the hydrothermally synthesized molybdenum disulfide (MoS2)-flowers to deal with energy and environmental issues related applications. MoS2-flowers were used as counter electrode material for the fabrication of dye-sensitized solar cells (DSSCs). Fabricated DSSCs showed power conversion efficiency (PCE) of 5.7% and open circuit voltage (Voc) of 0.76 V. Furthermore, MoS2-flowers was used as electrode modifier for the construction of 4-chlororhenol (4-CP). This modified MoS2-flowers based working electrode exhibited reasonable performance in terms of limit of detection and selectivity. A low detection limit of 0.39 µM with sensitivity of 11.47 µA/µMcm2 was achieved. MoS2-flowers demonstrated reasonable performance for DSSCs and 4-CP sensing applications.

Laser-induced graphene as a sustainable counter electrode for DSSC enabling flexible self-powered integrated harvesting and storage device for indoor application

Dye-sensitized solar cells (DSSCs) are gaining a newfound interest thanks to their superior ability to harvest indoor light with efficiency higher than other photovoltaic technologies. This study reports, for the first time, the possibility of using laser-induced graphene (LIG) as a flexible counter electrode material for DSSCs. A flexible LIG (F-LIG) electrode was fabricated by direct laser writing of a polyimide film, without the need of a starting conductive substrate. The prepared electrodes showed a higher catalytic activity towards the reduction of I3−/I−with respect to a more expensive Pt-based counter electrode. Moreover, the F-LIG electrodes outperformed electrodeposited PEDOT as a catalytic material for reduction of a copper bipyridyl complex (Cu(II/I)(tmby)2TFSI2/1) electrolyte. The F-LIG based DSSCs showed an open circuit voltage as high as 0.94 V and an increase in photoconversion efficiency higher than 60% with respect to the PEDOT-based counterpart, stepping from 3.08% to 4.96%. Thanks to the easy one-step laser-based fabrication process, the LIG-based DSSC was integrated with a LIG-based supercapacitor (SC), obtaining a flexible energy harvesting and storage system that was able to self-charge both under simulated solar illumination and under indoor artificial illumination, appearing to be a promising energy source for the next generation of self-powered connected Internet of Things devices.

Flexible Electrochromic Device on Polycarbonate Substrate with PEDOT:PSS and Color-Neutral TiO2 as Ion Storage Layer.

Electrochromic (EC) windows on glass for thermal and glare protection in buildings, often referred to as smart (dimmable) windows, are commercially available, along with rearview mirrors or windows in aircraft cabins. Plastic-based applications, such as ski goggles, visors and car windows, that require lightweight, three-dimensional (3D) geometry and high-throughput manufacturing are still under development. To produce such EC devices (ECDs), a flexible EC film could be integrated into a back injection molding process, where the films are processed into compact 3D geometries in a single automized step at a low processing time. Polycarbonate (PC) as a substrate is a lightweight and robust alternative to glass due to its outstanding optical and mechanical properties. In this study, an EC film on a PC substrate was fabricated and characterized for the first time. To achieve a highly transmissive and colorless bright state, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used as the working electrode, while titanium dioxide (TiO2) was used as the counter electrode material. They were deposited onto ITO-coated PC films using dip- and slot-die coating, respectively. The electrodes were optically and electrochemically characterized. An ECD with a polyurethane containing gel electrolyte was investigated with regard to optical properties, switching speed and cycling behavior. The ECD exhibits a color-neutral and highly transmissive bright state with a visible light transmittance of 74% and a bluish-colored state of 64%, a fast switching speed (7 s/4 s for bleaching/coloring) and a moderately stable cycling behavior over 500 cycles with a decrease in transmittance change from 10%to 7%.

One-step hydrothermal preparation of bi-functional NiS2/reduced graphene oxide composite electrode material for dye-sensitized solar cells and supercapacitors

To screen out suitable electrode materials and overcome the shortcomings of the existed electrode materials for the application in dye-sensitized solar cells and supercapacitors, NiS2/reduced graphene oxide (NiS2/rGO) composite material was prepared by a simple one-step hydrothermal method in this paper and applied in the field of both dye-sensitized solar cells and supercapacitors as electrode material. In an electrolyte of 6 M KOH, the NiS2/rGO composite material with bilayer capacitance characteristics exhibited a high specific capacitance of 259.20 F g−1 at the current density of 0.6 A g−1, which was significantly higher than that of rGO (188.94 F g−1). Moreover, at a current density of 2 A g−1, the NiS2/rGO composite material had 92.85% capacitance retention after 2000 cycles. When applied as counter electrode material for the dye-sensitized solar cells, the NiS2/rGO composite material counter electrode exhibited a satisfactory photoelectric conversion efficiency (η) of 3.16% under standard simulated sunlight (AM 1.5 G), which was significantly higher than that of single rGO counter electrode (improved by 90.40%). The NiS2/rGO composite electrode material prepared by a simple one-step hydrothermal method is a potential bi-functional composite electrode materials for both dye-sensitized solar cells and supercapacitors.

SET Kinetics of Ag/HfO2-Based Diffusive Memristors under Various Counter-Electrode Materials

The counter-electrode (CE) material in electrochemical metallization memory (ECM) cells plays a crucial role in the switching process by affecting the reactions at the CE/electrolyte interface. This is due to the different electrocatalytic activity of the CE material towards reduction-oxidation reactions, which determines the metal ion concentration in the electrolyte and ultimately impacts the switching kinetics. In this study, the focus is laid on Pt, TiN, and W, which are relevant in standard chip technology. For these, the influence of CE metal on the switching kinetics of Ag/HfO2-based volatile ECM cells is investigated. Rectangular voltage pulses of different amplitudes were applied, and the SET times were analyzed from the transient curves. The results show that CE material has a significant effect on the SET kinetics, with differences being observed depending on the voltage regime. The formation of interfacial oxides at the CE/electrolyte interface, particularly for non-noble metals, is also discussed in relation to the findings. Overall, this work highlights the important role of the CE material in the switching process of Ag/HfO2-based diffusive memristors and the importance of considering interfacial oxide formation in the design of these devices.

Facile fabrication of ZnCo2S4@MWCNT as Pt-free counter electrode for high performance dye-sensitized solar cells

Substitution of platinum as a counter electrode material in dye-sensitized solar cells (DSSCs) is critical because Pt is rare and expensive. In addition, Pt-based counter electrodes have problems with the long-term stability of DSSCs. Among Pt-free electrocatalysts, composite materials are of great interest because they can be advantageous due to the combined performance of their components. Here, we present a ternary ZnCo2S4 composite grown on multi-walled carbon nanotubes as a Pt-free counter electrode for the reduction of triiodide in DSSCs. The composite ZnCo2S4@MWCNT was synthesized in a simple two-step process: (i) spray coating of a MWCNT dispersion on a FTO glass substrate, followed by (ii) solvothermal growth of the ternary sulfide ZnCo2S4 on a MWCNT layer. Cyclic voltammetry analyzes showed superior electrocatalytic activity of the composite in the reduction of triiodide compared to Pt. Electrochemical impedance spectroscopy measurements of symmetric dummy cells showed lower charge transfer resistance of ZnCo2S4@MWCNT (RCT = 5.54 Ω × cm2) than the traditional Pt electrocatalyst (7.07 Ω × cm2) in catalyzing the triiodide-to-iodide conversion reaction. The photovoltaic measurements of dye-sensitized solar cells showed an improved conversion efficiency of ZnCo2S4@MWCNT (8.55%) with excellent stability compared to Pt (8.19%).

Amorphous Mixed-Vanadium-Tungsten Oxide Films as Optically Passive Ion Storage Materials for Solid-State Near-Infrared Electrochromic Devices.

Near infrared (NIR) electrochromic (EC) devices that selectively modulate the NIR light without affecting the daylight represent a promising window technology for saving energy consumption of buildings. Current research efforts have been focused on developing NIR-EC materials, while little attention has been directed to the optically passive ion storage materials that are crucial for balancing charges in a full NIR-EC device. Herein, we report that amorphous phase mixed-vanadium-tungsten oxide films exhibit minimum optical change with high ion storage capacity, which enables the usage of the mixed-metal oxides as optically passive counter electrode materials for NIR-EC devices. The mixed-vanadium-tungsten oxide films are synthesized by a room-temperature solution-based photodeposition method that allows us to precisely engineer the metal compositions and thicknesses of the mixed-metal oxide films, thus optimizing their optical inertness and ion storage capability. A solid-state NIR-EC device assembled with the mixed-vanadium-tungsten oxide film as an ion storage layer and the amorphous tungsten oxide hydrate as the NIR-EC layer shows fast response speed with cycling stability up to 10,000 cycles, proving the outstanding charge balancing capability of mixed-metal oxide. Our work provides an efficient strategy for developing optically passive ion storage films with high ion storage capability for high-performance EC devices.