IrOx Films Research Articles

Printable and Flexible Iridium Oxide-Based pH Sensor by a Roll-to-Roll Process

A flexible pH sensor based on using iridium oxide (IrOx) as the sensing film was developed by the roll-to-roll (R2R) process. The inert and biocompatible properties of IrOx make it a desired metal oxide for pH-sensing applications. The flexible substrates being continuously processed by the R2R technique provides the advantages of scalability, reconfigurability, resiliency, on-demand manufacturing, and high throughput, without the need for vacuum systems. Potential sweeps by cyclic voltammetry across the IrOx film against commercial and planar Ag/AgCl electrodes validated the reversible electrochemical mechanisms. Multiple IrOx electrodes showed similar output potentials when continuously tested in the pH range of 2–13, indicating good fabrication uniformity. For practical applications, planar IrOx/Ag-AgCl pairs developed on polyimide substrates were tested, with a good linear fit within pH 2–13, achieving Nernstian responses of around −60.6 mV/pH. The pH sensors showed good repeatability when analyzed with hysteresis, drift, fluctuation, and deviation as the stability factors. The selectivity of the interference ions and the effect of temperature were studied and compared with the reported values. The electrodes were further laminated in a process compatible with the R2R technique for packaging. The flexible sensors were tested under flat and curved surface conditions. Tests in artificial sweat and viscous solutions were analyzed in the Clarke error grid, showing reliable pH-sensing performance. The materials used during the manufacturing processes were sustainable, as the active materials were in small amounts and there was no waste during processing. No toxic chemicals were needed in the fabrication processes. The cost-effective and efficient materials and the fabrication process allow for rapid production that is necessary for disposable and point-of-care devices. Flexible electronics provide a platform for device and sensor integration and packaging, which enables Internet-of-things (IoT) network applications.

Electrocatalytic Reduction of O2 by ITO-IrOx: Implication for Dissolved Oxygen Sensor in the Alkaline Medium

Water pollution has badly affected human health, aquatic life, and the ecosystem. The purity of surface water can be measured in terms of dissolved oxygen (DO) measurements. Hence, it is desirable to have a portable and simple-to-use dissolved oxygen sensor. One possible remedy is an electrochemical sensor. Thus, we proposed an ITO-IrOx electrocatalyst for an effective and interference-free DO sensor utilizing the principle of oxygen reduction reaction (ORR). The ITO-IrOx was characterized using cyclic voltammetry (CV), scanning electron microscopy (SEM), electrochemical impedance spectrometry (EIS), X-ray photoelectron spectroscopy (XPS), and reflectance spectroscopy-based techniques. Reflectance spectra of the ITO-IrOx electrode showed the photoresist capability. The EIS spectra revealed lower charge transfer resistance for the ITO-IrOx electrode in ORR. The IrOx film on ITO exhibited a quick (one electron, α = 1.00), and reversible electron transfer mechanism. The electrode demonstrated high stability for oxygen sensing, having a limit of detection (LOD) of 0.49 ppm and interference-free from some common ions (nitrate, sulphate, chloride etc.) found in water.

Enhancing the repeatability and sensitivity of low-cost PCB, pH-sensitive field-effect transistors

Discrete, extended gate pH-sensitive field-effect transistors (dEGFETs) fabricated on printed circuit boards (PCBs) are a low-cost, simple to manufacture analytical technology that can be applied to a wide range of applications. Electrodeposited iridium oxide (IrOx) films have emerged as promising pH-sensitive layers owing to their theoretically high pH sensitivity and facile deposition, but typically exhibit low pH sensitivity or lack reproducibility. Moreover, to date, a combined IrOx and dEGFET PCB system has not yet been realised. In this study, we demonstrate a dEGFET pH sensor based on an extended gate manufactured on PCB that is rendered pH sensitive through an electrodeposited IrOx film, which can reliably and repeatably display beyond-Nernstian pH response. Using a combination of complementary surface analysis techniques, we show that the high pH sensitivity and repeatability of the dEGFETs are dependent on both the chemical composition and critically the uniformity of the IrOx film. The IrOx film uniformity can be enhanced through electrochemical polishing of the extended gate electrode prior to electrodeposition, leading to dEGFETs that exhibit a median pH sensitivity of 70.7 ± 5 mV/pH (n = 56) compared to only 31.3 ± 14 mV/pH (n = 31) for IrOx electrodeposited on non-polished PCB electrodes. Finally, we demonstrate the applicability of these devices by demonstrating the detection and quantification of ampicillin due to β-Lactamase enzyme activity, thus laying the foundation for cheap and ubiquitous sensors which can be applied to a range of global challenges across healthcare and environmental monitoring.

Batch Fabrication of Microminiaturized pH Sensor Integrated With IrO x Film and Solid State Ag/AgCl Electrode for Tap Water Quality Online Detection

Considering the indispensable of pH for tap water, a pH sensor with the characteristics of an implantable, long-term stable, and long lifetime is urgently needed for on-line and in situ pH monitoring in tap water, but this is always a challenging issue. In this article, a competitive integrated electrochemical pH sensor is developed and batch manufactured via micro-electro-mechanical system (MEMS). A dense and ultrasensitive IrOx electrode is obtained for almost 1.5 times Nernst response (−82.88 mV/pH), after preparation process optimization. A Si-Si3N4-KCl agar gel-polydimethylsiloxane (PDMS) multilayer structured Ag/AgCl electrode is designed and proven to be a long lifetime (>40 days) and be stable. By integrating with the IrOx film and solid-state Ag/AgCl electrode on a mini chip and verifying the effectiveness of the as-fabricated sensor by pH detection, the miniature pH sensor demonstrates wide detection range (1.8–12), stirring sensitivity, desirable linearity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{2}=0.999$ </tex-math></inline-formula> ), ideal repeatability and good resistance to other interference substances. Particularly, by employing the mass-production technique, favorable response consistency (relative standard deviation (RSD) < 2%) is witnessed, offering the opportunity to mass-produce the proposed sensor in the future. What’s more, the sensor still kept 91.7% sensitivity when compared to the sensitivity obtained at its initial state, after continuously operating for 32 days. Undoubtedly, the sensitive, durable, miniaturized, and mass-produced pH sensor proposed in this article is a competitive device to implant into the water pipeline for pH in situ online monitoring.

The Influence of Electrode Thickness on the Structure and Water Splitting Performance of Iridium Oxide Nanostructured Films.

For a safe environment, humanity should be oriented towards renewable energy technology. Water splitting (WS), utilizing a photoelectrode with suitable thickness, morphology, and conductivity, is essential for efficient hydrogen production. In this report, iridium oxide (IrOx) films of high conductivity were spin-cast on glass substrates. FE-SEM showed that the films are of nanorod morphology and different thicknesses. UV-Vis spectra indicated that the absorption and reflectance of the films depend on their thickness. The optical band gap (Eg) was increased from 2.925 eV to 3.07 eV by varying the spin speed (SS) of the substrates in a range of 1.5 × 103–4.5 × 103 rpm. It was clear from the micro-Raman spectra that the films were amorphous. The Eg vibrational mode of Ir–O stretching was red-shifted from 563 cm−1 (for the rutile IrO2 single crystal) to 553 cm−1. The IrOx films were used to develop photoelectrochemical (PEC) hydrogen production catalysts in 0.5M of sodium sulfite heptahydrate Na2SO3·7H2O (2-electrode system), which exhibits higher hydrogen evaluation (HE) reaction activity, which is proportional to the thickness and absorbance of the used IrOx photocathode, as it showed an incident photon-to-current efficiency (IPCE%) of 7.069% at 390 nm and −1 V. Photocurrent density (Jph = 2.38 mA/cm2 at −1 V vs. platinum) and PEC hydrogen generation rate (83.68 mmol/ h cm2 at 1 V) are the best characteristics of the best electrode (the thickest and most absorbent IrOx photocathode). At −1 V and 500 nm, the absorbed photon-to-current conversion efficiency (APCE%) was 7.84%. Electrode stability, thermodynamic factors, solar-to-hydrogen conversion efficiency (STH), and electrochemical impedance spectroscopies (EISs) were also studied.

Ellipsometry‐Based Approach for the Characterization of Mesoporous Thin Films for H2 Technologies

Porous thin layer materials are gaining importance in different fields of technology and pose a challenge to the accurate determination of materials’ properties important for their function. Herein, a hybrid measurement technique using ellipsometry together with other independent methods for validation, is demonstrated. Ellipsometry provides information about the porosity of different mesoporous films (PtRuNP/OMC = 45%; IrOx = 46%) as well as about the pore size (pore radius of ≈5 nm for PtRuNP/OMC). In addition, the electronic structure of a material, such as intraband transitions of a mesoporous IrOx film, can be identified, which can be used to better understand the mechanisms of chemical processes. In addition, it is shown that ellipsometry can be used as a scalable imaging and visualization method for quality assurance in production. These require accurate and traceable measurements, with reference materials playing an important role that include porosity and other related properties. It is shown that novel analytical methods are useful for improving analytical work in this entire field.

Electrocatalytic oxidation of catechol using IrOx-ITO electrode in aqueous medium

• IrOx film was fabricated on ITO glass with electro flocculation method. • Ir(III)/Ir(IV) redox couple catalyzes catechol oxidation reactions in the acidic medium. • Catechol may be used as fuel in a fuel cell. • IrOx-ITO film is extremely stable in attaining catechol oxidation. Catechol is extracted from the wastes of oil refineries which is source of o-benzoquinone, the starting material for many organic syntheses. Catechol can produce o-benzoquinone by releasing two electrons via a reversible reaction which could be exploited for fuel cell construction. Thus, for conversion of catechol into o-benzoquinone is crucial and requires a robust catalyst. In the present article, we propose IrO x immobilized ITO surface for efficient electrocatalytic oxidation of catechol. The catalysis and kinetics have been investigated using Cyclic Voltammetric (CV) technique in acidic medium. The Ir(III) species involves one electron transfer redox reaction on the ITO surface and the conversion of Ir(III) to Ir(IV) has been identified to catalyze catechol oxidation reaction. The concentration of the electro active Ir species on the ITO surface was calculated to be (3.32 ± 0.22) × 10 −9 mol cm −2 .

JULIEs: nanostructured polytrodes for low traumatic extracellular recordings and stimulation in the mammalian brain

Objective. Extracellular microelectrode techniques are the most widely used approach to interrogate neuronal populations. However, regardless of the manufacturing method used, damage to the vasculature and circuit function during probe insertion remains a concern. This issue can be mitigated by minimising the footprint of the probe used. Reducing the size of probes typically requires either a reduction in the number of channels present in the probe, or a reduction in the individual channel area. Both lead to less effective coupling between the probe and extracellular signals of interest. Approach. Here, we show that continuously drawn SiO2-insulated ultra-microelectrode fibres offer an attractive substrate to address these challenges. Individual fibres can be fabricated to >10 m continuous stretches and a selection of diameters below 30 µm with low resistance (<100 Ω mm−1) continuously conductive metal core of <10 µm and atomically flat smooth shank surfaces. To optimize the properties of the miniaturised electrode-tissue interface, we electrodeposit rough Au structures followed by ∼20 nm IrOx film resulting in the reduction of the interfacial impedance to <500 kΩ at 1 kHz. Main results. We demonstrate that these ultra-low impedance electrodes can record and stimulate both single and multi-unit activity with minimal tissue disturbance and exceptional signal-to-noise ratio in both superficial (∼40 µm) and deep (∼6 mm) structures of the mouse brain. Further, we show that sensor modifications are stable and probe manufacturing is reproducible. Significance. Minimally perturbing bidirectional neural interfacing can reveal circuit function in the mammalian brain in vivo.

Growth conditions and mechanisms for IrOx nano-platelet formation by reactive sputtering

Iridium oxide (IrOx) forms a wide array of tailorable nanostructures, including plates, rods, and cones. Despite a strong body of literature on nanostructured IrOx, prior work did not explore the specific growth conditions and mechanisms for platelet formation. Here we report on how IrOx nanoplatelets take their form during DC reactive sputtering deposition, highlight the conditions and growth mechanisms that lead to unique nanostructures, and demonstrate changes in morphology and crystal orientation via x-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy and x-ray photoelectron spectroscopy. The XRD spectra indicate that IrOx undergoes a substantial transition with increasing oxygen flow rate during deposition, with the initial face-centered cubic (111), (200) and (220) peaks vanishing, while the rutile (101) and (110) peaks emerge, with several intermediate peaks indicating transition species. Ultimately (101) emerges as the preferred orientation of the IrOx nanostructures, as evidenced by the time-series XRD spectra. Corresponding stress analysis indicates that in the absence of oxygen flow, the IrOx films are highly compressive, and that the film stress becomes significantly less compressive with increasing oxygen flow. This unlocks the use of IrOx as a highly tailorable nanostructured material, ranging from dense film to high aspect ratio platelets, by simply adjusting oxygen flow rate and/or sputtering time.

A Comparative Study of Fabricating IrOx Electrodes by High Temperature Carbonate Oxidation and Cyclic Thermal Oxidation and Quenching Process

IrOx electrodes were fabricated by cyclic thermal heating and water quenching (CHQ) process and high temperature carbonate oxidation (HCO), respectively. By examining the E-pH relationship, response rate, potential drift behavior of the fabricated electrodes, the electrodes prepared by CHQ process seemed to show better comprehensive performance. Characterization tests such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) were used to characterize the fabricated IrOx electrodes and find out the reason for the better performance of the electrodes prepared by CHQ process. Morphology tests indicate that the CHQ electrode shows a multi-layer structure with more ion channels, which could provide larger surface area for the H+ response process. Furthermore, combining the XPS, Raman and EIS tests etc., more effective response composition, better crystal quality, and smaller response reaction resistance of surface IrOx film could account for the better performance of the CHQ-fabricated IrOx electrode. The film formation process, H+ response mechanism, as well as the response behavior difference between the two kinds of the electrodes are further elaborated.

Self-supported amorphous iridium oxide catalysts for highly efficient and durable oxygen evolution reaction in acidic media

Developing highly active and stable electrocatalysts for acidic oxygen evolution reaction is still a great challenge. Herein, we developed a novel self-supported amorphous IrOx catalyst (IrOx/Ti) encapsulated with a small number of crystalline nanoparticles for efficient acidic OER. The resulting IrOx-50-AC/Ti electrode exhibits a superior OER performance with an overpotential of 250 mV at 10 mA cm−2 and Tafel slope of 50.4 mV dec−1 in 0.1 M HClO4. High contents of IrIII species and surface hydroxide groups, hierarchically porous structure and high defective density contribute to boost the OER activity. Importantly, the amorphous IrOx-50-AC/Ti also demonstrates a super long-term durability for 190 h due to the strong interaction between IrOx film and Ti. The unique amorphous-crystalline structure also enhances the stability and the activity by promoting the synergy between amorphous phase and crystalline phase. This work provides some valuable insights on developing efficient Ir-based catalysts for acidic water splitting.

Electrocatalytic Oxidation of Water by OH−‐ and H2O‐Capped IrOx Nanoparticles Electrophoretically Deposited on Graphite and Basal Plane HOPG: Effect of the Substrate Electrode**

AbstractIridium oxide (IrOx) is one of the most efficient electrocatalysts for water oxidation reaction (WOR). Here, WOR electrocatalysis by 1.6 nm IrOx nanoparticles (NPs) electrophoretically deposited onto spectroscopic graphite (Gr) and basal plane highly ordered pyrolytic graphite (HOPG) was studied as a function of NPs’ capping ligands and electrodeposition substrate. On Gr, OH−‐ and H2O‐capped NPs exhibited close sub‐monolayer surface coverages and specific electrocatalytic activity of 18.9‐23.5 mA nmol−1 of IrIV/V sites, at 1 V and pH 7. On HOPG, OH−‐capped NPs produced films with a diminished WOR activity of 5.17±2.40 mA nmol−1. Electro‐wettability‐induced changes impeded electrophoretic deposition of H2O‐capped NPs on HOPG, WOR currents being 25‐fold lower than observed for OH−‐capped ones. The electrocatalysis efficiency correlated with hydrophilic properties of the substrate electrodes, affecting morphological and as a result catalytic properties of the formed IrOx films. These results, important both for studied and related carbon nanomaterials systems, allow fine‐tuning of electrocatalysis by a proper choice of the substrate electrode.

Electrochemically deposited iridium-oxide: Estimation of intrinsic activity and stability in oxygen evolution in acid solution

Hydrated iridium oxyhydroxide (IrOx) films were electrochemically deposited from an alkaline oxalic solution at constant anodic potentials and by applying a potential cycling protocol, in both cases with variation of the electrodeposition time. From UV–vis spetroscopy of the solution for the deposition and their characterization it was concluded that a mixture of Ir(III)/Ir(IV) monomers participates in the deposition of IrOx film. X-ray photoelectron spectroscopy (XPS) of IrOx films indicated that both types of films contained hydrated Ir(IV) hydroxide as the dominant species, but in the film deposited by potential cycling the presence of the additional Ir(III) species was evident. The scanning electon microscopy (SEM) analysis of the surface morphology revealed that films deposited by potential cycling were more uniform than the films deposited at a constant potential. The amount of electrochemically active Ir-species on the surface of deposited IrOx films was estimated from the voltammetric charge of the Ir(III)/Ir(IV) transition. Depending on the film electrodeposition parameters, the values between 15 and 1080 nmol cm−2 were obtained. The electrochemically active surface area (ECSA) of IrOx films was calculated from cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements and ranged from 3 to 131 cm2 per 1 cm2 of geometric surface area for various films. The activity and stability of IrOx films toward oxygen evolution reaction (OER) was investigated in 0.5 M H2SO4 solution under potentiostatic conditions. The intrinsic activity, stated as turnover frequency and specific current density normalized per ECSA, showed that the OER activity of IrOx films deposited by potential cycling are up to two and a half times higher than the activity of films deposited at a constant anodic potential. Potentiostatic stability test showed a decrease in OER current over time for both type of the films. Determination of ECSA, the amount of electroactive Ir species, XPS spectrum and SEM imaging after the test indicated that the decrease in OER activity was caused by partial dissolution and delamination of the film as well as by oxidation of highly active hydroxide Ir(III) species.

A Comparative Study of Fabricating IrOx Electrodes By Cyclic Thermal Oxidation and High Temperature Carbonate Oxidation

IrOx electrodes were fabricated by cyclic thermal heating and water quenching (H&Q) process and high temperature carbonate oxidation, respectively. By examining the E-pH relationship, response rate, potential drift behavior of the fabricated electrodes, the electrodes prepared by H&Q process seemed to show better comprehensive performance. Characterization tests such as scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), electrochemical impedance spectrum (EIS), etc. were used to characterize the fabricated IrOx electrodes and find out the reason for the better performance of the electrodes prepared by H&Q process. Morphology tests show that the H&Q electrode show a relative multi-layer structure, which could provide larger surface area for the H+ response process. At the meantime, combining the XPS and EIS test etc., more effective response composition, smaller response reaction of surface IrOx film could account for the better performance of the IrOx electrode.

Patterned iridium oxide film as neural electrode interface: Biocompatibility and improved neurite outgrowth with electrical stimulation

Iridium (Ir) thin film was deposited on patterned titanium substrate by direct-current (DC) magnetron sputtering, and then activated in sulfuric acid (H2SO4) through repetitive potential sweeps to form iridium oxide (IrOx) as neural electrode interface. The resultant IrOx film showed a porous and open morphology with aligned microstructure, exhibited superior electrochemical performance and excellent stability. The IrOx film supported neural stem cells (NSCs) attachment, proliferation and improved processes without causing toxicity. The patterned IrOx films offered a unique system to investigate the synergistic effects of topographical cue and electrical stimulation on neurite outgrowth. Electrical stimulation, when applied through patterned IrOx films, was found to further increase the neurite extension of neuron-like cells and significantly reorient the neurite alignment towards to the direction of stimulation. These results indicate that IrOx film, as electrode-tissue interface is highly stable and biocompatible with excellent electrochemical properties.

Facile fabrication and nanostructure control of mesoporous iridium oxide films for efficient electrocatalytic water oxidation

The development of efficient catalyst materials for water oxidation is bottleneck to construct artificial photosynthesis that is a promising future energy-providing system. We review the recent progress on development of IrOx electrocatalyst films for water oxidation based on our latest research works. A controlled fabrication approach of an efficient IrOx electrocatalyst films is introduced by a facile spin-coating of a homogenous solution of Ir precursor complexes followed by simple annealing at different temperature. The composition and crystallinity of the IrOx film are tunable by a simple annealing treatment. The electrocatalytic properties of the IrOx film dramatically depended on annealing temperature are characterized to give the noticeably high performance at 300 °C annealing. A soft-template-assisted technique using different polymer surfactants as structure directing agents (SDAs) is illustrated in the spin-coating procedure to reveal impacts of SDAs on nanostructures and electrocatalytic water oxidation performances of the IrOx films. The characterization of the first accessible channel-like open pore architecture of the ordered 2D-hexagonal mesoporous IrOx film is described by a facile one-pot strategy using Pluronic F127 as SDA. The novel controlled nanostructures including mesoporous architecture of IrOx improves electrocatalytic performance for water oxidation relative to a conventional nanoparticulate structure of IrOx coating.

Morphological, surface and optical properties of spin-coated IrOx films; influence of spin speed, annealing and (Cr, La) codoping

Iridium oxide (IrOx) is a fascinating metal oxide with superior chemical/physical properties. The present report is an attempt to tune the surface and optical properties of IrOx to widen its industrial and technological applications. The influences of substrates' rotational speed (RS), annealing temperature (AT), Cr-doping and (Cr, La) codoping on the surface morphology and wettability, structural as well as the optical properties of spin-coated IrOx films are discussed. Raman spectra of the films show a characteristic phonon mode at 552 cm−1, arising from the Ir–Ox stretching and influenced significantly by the preparative conditions (RS and AT) as well as (Cr, La) codoping. Energy-dispersive X-ray spectra were obtained to confirm the chemical compositions of prepared IrOx nanostructure thin films. Field emission-scanning electron microscopy images reveal the growth of undoped, Cr-doped and (Cr, La) codoped nanorod-like IrOx structures. The annealed film at 500 °C and Cr-doped films showed the nanoporous nature of the grown nanorod-like structures. The films are hydrophilic and follow the Wenzel model. The wetting ability is enhanced by decreasing RS and increasing AT. Increasing RS results in increasing the transmittance (T%) due to decreasing the films' thickness. At wavelength λ = 103 nm, the deposited film shows T% = 53.2 and the film annealed at 500 °C exhibits T% = 44.3. The optical band gap (Egop) increased with increasing RS and decreased with increasing AT. Cr-doping redshifted Egop from 2.95 to 2.85 eV, while codoping with La blue shifted Egop to 3.14 eV. The effect of Cr and La doping on the optical constants of IrOx films was investigated and compared with those of other transition metal oxide films because no data are available in the literature for IrOx films.

Facile and sustainable fabrication of transparent mesoporous IrOx films formed by nanoparticle assembly for efficient electrocatalytic water oxidation

A new transparent mesoporous IrOx film consisting of small interconnected nanoparticles has been developed by a simple drop-cast method to provide an efficient electrocatalyst film for water oxidation.

Fabrication of Iridium Oxide/Platinum Composite Film on Titanium Substrate for High-Performance Neurostimulation Electrodes

Electrode materials for neural stimulation have been widely investigated for implantable devices. Among them, iridium and iridium oxide are attractive materials for bio-interface applications due to their desirable stability, electrochemical performance, and biocompatibility. In this study, iridium oxide/platinum (IrOx/Pt) composite films were successfully fabricated on titanium substrates by chemical bath deposition and these films are expected to be used as biocompatible stimulation electrodes. We modified the film compositions to optimize the performances. In addition, these IrOx/Pt composite films were characterized before and after annealing by SEM and XRD. We also identified the hydrophilicity of these iridium oxide/platinum composite films by measuring contact angles. Finally, the charge storage capacities of these iridium oxide/platinum composite films were evaluated by an electrochemical workstation. As a result, the charge storage capacities of the iridium oxide/platinum composite films are largely increased, and this leads to a very efficient neurostimulation electrode. Additionally, we successfully demonstrated the chemical bath deposition of IrOx film on the surface of the bullet-shaped titanium microelectrode.

Iridium oxide catalyst for hybrid electrochromic device based on tetramethylthiourea (TMTU) redox electrolyte

This work reports a study on sputter coated iridium oxide film as a counter electrode (CE) for the electrochemical catalysis of tetramethylthiourea/tetramethylformaminium disulfide (TMTU/TMFDS2+) redox reaction in electrochromic (EC) devices. The iridium oxide (IrOx) with the thickness of about 5 nm coated onto transparent conductive oxide, e.g., fluorine-doped tin oxide (F:SnO2), has shown excellent catalytic properties and excellent electrochromic cycling stability in EC device. The electrochemical impedance spectroscopy (EIS) results revealed that the charge transfer resistance (Rct) is mainly influenced by the oxygen flow rate during the sputtering process, and by the layer thickness. The IrOX films coated with low oxygen flow rate has shown a lower charge transfer resistance compared to the fully oxidized iridium oxide film. However, sub-stoichiometric layers are less transparent, and therefore less appropriate for the application. In this regard, fully oxidized and highly transparent (Tvisible = 86%) layer formed by the sputtering process at or above 50 sccm (standard cubic centimeters per minute) flow of oxygen having the thickness of 5 nm is used in EC devices. These layers have the Rct of 25 Ω cm2 at 1 V bias voltage for the redox electrolytes. The cyclic voltammetry technique has shown a typical quasi-reversible nature of redox electrolyte at the same IrOx coated electrode. An electrochromic test for 550 cycles demonstrates that 5 nm of IrOx is sufficient for the stabile EC window with TMTU/TMFDS2+ electrolyte.