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Operando observation of chemical transformations of iridium oxide during photoelectrochemical water oxidation
摘要： Iridium oxide is one of the few catalysts capable of catalyzing the oxygen evolution reaction (OER) in both acidic and basic conditions. Understanding the mechanism of IrOx under realistic photoelectrochemical conditions is important for the development of integrated water splitting systems. Herein, we have developed a highly efficient OER photoanode in pH 1 aqueous solutions based on a sputtered IrOx film and a p+n-Si light absorber, interfaced with sputtered Au layer. Operando high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS) was employed to monitor the oxidation state changes of IrOx during both electrochemical and photoelectrochemical (PEC) water oxidation reactions in pH 1 aqueous solutions. We observed a gradual increase of the average oxidation state of Ir with increasing anodic potential in the pre-catalytic region, followed by a reduction of Ir under O2 evolution conditions. Consistent results were obtained on dark anodes and illuminated photoanodes. However, when the thickness of IrO2 was increased to 2 and 3 nm, the spectral changes became much less pronounced and the reduction of Ir oxidation state after the OER onset was not observed. This is due to the lower surface to bulk ratio, where lattice oxygen sites in the bulk are not accessible for the formation of hydroxide. More generally, the operando method developed here can be extended to other materials, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.
关键词： oxygen evolution reaction (OER),electrochemical and photoelectrochemical (PEC),high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD XAS),iridium oxide,Operando method
更新于2025-09-23 15:23:52
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Gas Sensing with Iridium Oxide Nanoparticle Decorated Carbon Nanotubes
摘要： The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrOx-MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrOx nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH3 and NO2 than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed.
关键词： carbon nanotubes,relative humidity effect,metal nanoparticles,iridium oxide,chemoresistive gas sensor
更新于2025-09-23 15:22:29
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Enhanced Oxygen Evolution Reaction Activity of Nanoporous SnO <sub/>2</sub> /Fe <sub/>2</sub> O <sub/>3</sub> /IrO <sub/>2</sub> Thin Film Composite Electrodes with Ultralow Noble Metal Loading
摘要： A conductive SnO2 layer and small quantities of IrO2 surface cocatalyst enhance the catalytic efficiency of nanoporous Fe2O3 electrodes in the oxygen evolution reaction at neutral pH. Anodic alumina templates are therefore coated with thin layers of SnO2, Fe2O3, and IrO2 by atomic layer deposition. In the first step, the Fe2O3 electrode is modified with a conductive SnO2 layer and submitted to different postdeposition thermal treatments in order to maximize its catalytic performance. The combination of steady-state electrolysis, electrochemical impedance spectroscopy, X-ray crystallography, and X-ray photoelectron spectroscopy demonstrates that catalytic turnover and e? extraction are most efficient if both layers are amorphous in nature. In the second step, small quantities of IrO2 with extremely low iridium loading of 7.5 μg cm?2 are coated on the electrode surface. These electrodes reveal favorable long-term stability over at least 15 h and achieve maximized steady-state current densities of 0.57 ± 0.05 mA cm?2 at η = 0.38 V and pH 7 (1.36 ± 0.10 mA cm?2 at η = 0.48 V) in dark conditions. This architecture enables charge carrier separation and reduces the photoelectrochemical water oxidation onset by 300 mV with respect to pure Fe2O3 electrodes of identical geometry.
关键词： iridium oxide,water splitting,nanostructures,iron oxide,atomic layer deposition
更新于2025-09-10 09:29:36
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Electrochromic Properties of Sputtered Iridium Oxide Thin Films with Various Film Thicknesses
摘要： Iridium oxide is an anodic electrochromic material, which takes on a blue-black color through electrochemical oxidation and turns to transparent via reduction. Hydrated amorphous Ir oxide thin films with various thicknesses from 20 to 400 nm were prepared by reactive sputtering in a H2O atmosphere, and their transmittance spectra in both the bleached and colored states as well as their response times were examined in this study. The bleached and colored transmittances decreased with increasing film thickness according to Lambert’s law, and the absorption coefficients in the bleached and colored states were estimated to be 3.2 × 103 and 1.1 × 105 cm-1, respectively, at a wavelength of 600 nm. The results point to almost all the Ir atoms being electrochemically active and contributing to the color change. A maximum transmittance change of 81% was obtained for the 400 nm-thick film. Further, there was a trade-off between the response speed and the transmittance change. The response speed slowed down with increasing the film thickness, while the coloring and bleaching response time for the thick films was several tens of seconds.
关键词： electrochromic,optical transmittance,iridium oxide
更新于2025-09-09 09:28:46
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Iridium oxide (IV) nanoparticle-based electrocatalytic detection of PBDE
摘要： Polybrominated diphenyl ethers (PBDEs) are a type of flame retardants which are currently banned in EU and USA due their hazardousness for humans and mammals. However, these compounds were highly used during more than 30 years and still persist in the environment since they are resistant to degradation. Herein we present a biosensor for the detection of PBDEs using screen printed carbon electrodes (SPCEs) based on the electrochemical monitoring of water oxidation reaction (WOR) catalyzed by iridium oxide (IV) nanoparticles (IrO2 NPs). Our assay shows a limit of detection of 21.5 ppb of PBDE in distilled water. We believe that such an IrO2 NPs-based electrocatalytic sensing system can lead to a rapid, sensitive, low cost and miniaturizable device for the detection of PBDEs.
关键词： PBDEs,Electrocatalysis,Iridium Oxide Nanoparticles,Flame retardants,Screen Printed Carbon Electrodes
更新于2025-09-09 09:28:46
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Iridium oxide catalyst for hybrid electrochromic device based on tetramethylthiourea (TMTU) redox electrolyte
摘要： 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.
关键词： Sputter coating,Redox electrolyte,Iridium oxide,Electrochromic device,Tetramethylthiourea
更新于2025-09-04 15:30:14
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Electrochemical Effects of Depositing Iridium Oxide Nanoparticles onto Conductive Woven and Nonwoven Flexible Substrates
摘要： This Article reports methods to deposit iridium oxide nanoparticles (IrOx NPs) onto ?exible materials for charge storage and the stable charge?discharge mechanism. In this work, IrOx NPs were electrodeposited onto commercially available ?exible surfaces of both knit and nonwoven cotton and nonwoven carbon-based (carbon nanotubes and graphene) textile substrates. Carbon-coated cotton materials were fabricated by reducing graphene oxide on fabric. Flexible electrode materials were fabricated by either reducing graphene oxide on cotton fabric or binding carbon nanotubes/graphene into a free-standing platform. The IrOx NPs were then electrodeposited onto ?exible platform samples by applying a positive potential to the fabric. After deposition, the resultant speci?c capacitance of the materials increased within the range from 192% to 2747% and was stable for over 1000 charge and discharge cycles.
关键词： ?exible materials,iridium oxide nanoparticles,?exible substrates,electrodeposition
更新于2025-09-04 15:30:14