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AbstractIn this study, the first sensitive voltammetric nanosensor was developed for the determination of metrafenone. For this purpose, iridium oxide nanoparticles (IrOxNPs) were synthesized, and a nanocomposite was formed on the glassy carbon electrode with IrOxNPs and an ionic liquid (IL). The influence of pH on the metrafenone response was examined using phosphate and Britton-Robinson buffers as a function of pH. The influence of scan rate on the response to metrafenone was investigated in pH 7.0 phosphate buffer where the highest peak current was obtained and the peak shape was good. It was concluded that the oxidation occurred by the adsorption and diffusion mechanisms. According to cyclic voltammetry measurements for metrofenone, a single irreversible anodic peak was observed in all buffer solutions. Using the relationship between the peak potential and the logarithm of the scan rate, the electron number for the oxidation process was determined to be 2. Using adsorptive stripping differential pulse voltammetry, the detection limits for standard and the serum samples were 0.08 mg/L and 0.07 mg/L, respectively, and the calibration curve was linear up to 1.4 mg/L. The developed nanosensor was also employed to analyze to commercial preparations and good recovery values were obtained. [ABSTRACT FROM AUTHOR]

Iridium oxide is the state‐of‐the‐art catalyst for electrochemical water oxidation in an acidic medium. Despite being one of the rarest elements in the Earth's crust, there is a pressing need to maximize the utilization and longevity of active iridium centers. While conventional low‐temperature synthesis can yield nanostructures with high mass‐specific activity, they are often insufficiently stable during water oxidation. Structurally ordered iridium oxide is one of the most stable electrocatalysts utilized in polymer electrolyte membrane water electrolysis that benefits from the chemically ordered structure. However, its preparation requires thermal treatment at high temperatures, which improves its durability but can also result in reduced surface area and altered particle morphology. In this study, the challenge of controlling nanoparticle size during the preparation of structurally ordered iridium oxide is successfully addressed, which typically requires high‐temperature thermal treatment. By utilizing a silica nanoreactor as a hard template, a precise control is achieved over the nanoparticle size during high‐temperature thermal treatment. This approach maintains high durability while avoiding the common problem of reduced surface area and altered particle morphology. Specifically, this study is able to synthesize iridium oxide nanoparticles at temperatures up to 800 °C, while keeping their dimensions below 10 nm. [ABSTRACT FROM AUTHOR]

As the current pandemic has shown, lateral flow assays (LFAs) are a prime example of point-of-care devices enabling quick testing at an affordable price. However, their ease of use undeniably affects their sensitivity, making them less sensitive than other multi-step and time-consuming diagnostic assays, such as polymerase chain reactions and enzyme-linked immunosorbent assays. A possible solution to overcome this lack of sensitivity is the exploitation of bottom-up approaches to synthesize nanomaterials with outstanding properties for use as colorimetric labels in LFAs, that is, using nanoparticles with better optical capabilities to improve the generation of the colorimetric signal and the overall sensitivity of LFAs. Following this strategy, we rationally optimized the synthesis of gold and iridium oxide nanoflowers (Au–IrO2 NFs) to enhance their physical–chemical properties as colorimetric labels in LFAs. Specifically, we were able to rationally control their size (from 155 to 53 nm in diameter) in order to guarantee an optimal flow along the different pads of a LFA. Moreover, thanks to their superior plasmonic behavior (compared to standard AuNPs), we could achieve an 8.5-fold lower limit of detection (down to 1.2 ng/mL) for human immunoglobulin G (HIgG) than standard LFAs (10.1 ng/mL). Therefore, due to their optical and redox properties, bioconjugation capabilities, and synergic combination of the individual components, Au–IrO2 NFs appear as potential candidates for the next generation of optical LFAs. [ABSTRACT FROM AUTHOR]

Bisphenol S (BPS) is a common pollutant in the environment and has posed a potential threat to aquatic animals and human health. To accurately assess the pollution level and ecological risk of BPS, there is an urgent need to establish simple and sensitive detection methods for BPS. In this study, BPS complete antigen was successfully prepared by introducing methyl 4-bromobutyrate and coupling bovine serum albumin (BSA). The monoclonal antibody against BPS (anti-BPS mAb) with high affinity (1: 256,000) was developed based on the BPS complete antigen, which showed low cross-reactivity with BPS structural analogues. Then, an electrochemical immunosensor was constructed to detect BPS using multi-walled carbon nanotubes and gold nanoflower composites as signal amplification elements and using anti-BPS mAb as the probe. The electrochemical immunosensor had a linear range from 1 to 250 ng⋅mL−1 and a limit of detection (LOD) down to 0.6 ng⋅mL−1. Additionally, a more stable and sensitive lateral flow immunoassay (LFIA) for BPS was developed based on iridium oxide nanoparticles, with a visual detection limit of 1 ng⋅mL−1, which was 10 times lower than that of classical Au-NPs LFIA. After evaluation of their stability and specificity, the reliability of these two methods were further validated by measuring BPS concentrations in the water and fish tissues. Thus, this study provides sensitive, robust and rapid methods for the detection of BPS in the environment and organisms, which can provide a methodological reference for monitoring environmental contaminants. [Display omitted] • High specificity and affinity anti-BPS monoclonal antibodies were prepared. • An electrochemical immunosensor was developed using Au NFs and MWCNTs. • A stable and sensitive nanoparticle called IrO 2 NPs was synthesized. • IrO 2 NPs based LFIA was established to rapid detection of BPS. • This study offered sensitive and robust detection methods for BPS. [ABSTRACT FROM AUTHOR]

Significantly reducing the iridium content in oxygen evolution reaction (OER) catalysts while maintaining high electrocatalytic activity and stability is a key priority in the development of large-scale proton exchange membrane (PEM) electrolyzers. In practical catalysts, this is usually achieved by depositing thin layers of iridium oxide on a dimensionally stable metal oxide support material that reduces the volumetric packing density of iridium in the electrode assembly. By comparing two support materials with different structure types, it is shown that the chemical nature of the metal oxide support can have a strong influence on the crystallization of the iridium oxide phase and the direction of crystal growth. Epitaxial growth of crystalline IrO 2 is achieved on the isostructural support material SnO 2 , both of which have a rutile structure with very similar lattice constants. Crystallization of amorphous IrO x on an SnO 2 substrate results in interconnected, ultrasmall IrO 2 crystallites that grow along the surface and are firmly anchored to the substrate. Thereby, the IrO 2 phase enables excellent conductivity and remarkable stability of the catalyst at higher overpotentials and current densities at a very low Ir content of only 14 at%. The chemical epitaxy described here opens new horizons for the optimization of conductivity, activity and stability of electrocatalysts and the development of other epitaxial materials systems., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Catalytic nitrobenzene reduction is crucial for the synthesis of 4,4-methylene diphenyl diisocyanate, which is used to produce polyurethane foams, thermoplastic elastomers, and adhesives. The stability and activity of nanoparticle catalysts are affected by surface ligands and stabilizers. We established the complete composition of 7.0 ± 1.1 nm iridium oxide nanoparticles that were stabilized by polyvinylpyrrolidone (PVP[Ir]). PVP[Ir] and its surface stabilizers were characterized using elemental analysis (EA), high-resolution X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), FT-IR, and UV-vis spectroscopy. Notably, PVP[Ir] contained 33.8 ± 0.4% Ir. XPS binding energy analyses suggest that 7% of the Ir is Ir(0) and 93% is IrO2. Using formic acid as the source of hydrogen, PVP[Ir] catalyzed the selective hydrogenation of nitrobenzene to give aniline as the only product in 66% yield in 1 h at 160 °C in a high-pressure metal reactor. Less than 1% of the side products (azobenzene and azoxybenzene) were detected. In contrast, using alcohol as the hydrogen source led to a low yield and a poor selectivity for aniline.

We demonstrate the fabrication of a flexible and conductive bioelectrode via the electrodeposition of IrO 2 nanoparticles on a metalized polypropylene micromembrane (PPMM). The metalized PPMM is prepared by carrying out conformal electroless deposition of Au on individual polypropylene (PP) fibers of PPMM using both polydopamine and polyvinyl alcohol as the surface–modifying agents to improve the hydrophilicity of PPMM. Images from scanning and transmission electron microscopes, as well as analysis from energy dispersive X–ray spectrometer and X–ray photoelectron spectroscopy confirm the successful formation of IrO 2 nanoparticles on individual PP fibers of metalized PPMM. For bio–stimulating purpose, the IrO 2 –coated PPMM reveals an impressive charge–storage–capacity of 54.6 mC/cm2 in cyclic voltammetry, In addition, under a symmetric bi–phasic current pulse, its charge–injection–capacity reaches 466 μC/cm2. Since the entire constituents for the IrO 2 –coated PPMM are bio−compatible, we envision its potential use as a bioelectrode in implantable biomedical devices. [ABSTRACT FROM AUTHOR]

For hydrogen production by water electrolyzers, iridium dioxide (IrO2) works as a catalyst for oxygen evolution reaction (OER) at an anode. In this report, we aim to study the formation mechanism of IrO2 nanoparticles on graphene by inducing nanoscale defects artificially. The defects on graphene grown on a copper foil by chemical vapor deposition were created by UV-ozone treatment, and IrO2 nanoparticles were deposited by hydrothermal synthesis method. We investigated the amount of defects and oxygen-functional groups on graphene by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The size and distribution of defects and IrO2 nanoparticles on graphene were analyzed by atomic force microscopy (AFM). Raman spectroscopy and XPS measurement showed that defects and oxygen-functional groups increased with the UV-ozone treatment time. The size of IrO2 nanoparticles was reduced to ca. 4.5 nm on defective graphene, whereas the nanoparticles deposited on pristine graphene is ca. 8.8 nm in diameter. It is found that the IrO2 nanoparticles were deposited and anchored on the edge of hole-like defects on graphene. In addition, the size of deposited nanoparticles can be controlled by the extent of modification in graphene.

Iridium 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 mAnmol-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 mAnmol-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. [ABSTRACT FROM AUTHOR]

Abstract Lateral flow biosensors are paper-based devices that allow the detection of different types of analytes with quickness, robustness and selectivity, without leaving behind paper sensors benefits as low-cost, recyclability and sustainability. Nanomaterials have been widely reported in lateral flow biosensors, offering new sensing strategies based on optical or electrical detection techniques. Looking for other advantageous nanomaterials, we propose for the first time the use of iridium oxide (IV) nanoparticles in lateral flow assays for the detection of human immunoglobulin as a model protein. These nanoparticles can be easily prepared and conjugated with biomarkers. Their dark blue color gives a high contrast against the white background of the strips being in this way excellent labels. Graphical abstract fx1 Highlights • Iridium oxide (IV) nanoparticles have been applied for the first time as tags on a lateral flow assay. • Iridium oxide nanoparticles exhibit intense blue color and high biocompatibility with antibodies. • The application of iridium oxide (IV) nanoparticles doubles the sensitivity of the classical gold nanoparticle-based lateral flow. [ABSTRACT FROM AUTHOR]

Abstract 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 (IrO 2 NPs). Our assay shows a limit of detection of 21.5 ppb of PBDE in distilled water. We believe that such an IrO 2 NPs-based electrocatalytic sensing system can lead to a rapid, sensitive, low cost and miniaturizable device for the detection of PBDEs. Graphical abstract fx1 Highlights • IrO 2 nanoparticle tags are detected through the electrocatalytic water oxidation reaction (WOR) in aqueous buffer. • Both screen printed carbon electrodes and IrO 2 nanoparticles are robust against temperature and stable in time. • A LOD of 21.5 ppb, similar to the available commercial ELISA kits, is achieved but being faster and cheaper, avoiding the use of enzymes. [ABSTRACT FROM AUTHOR]

Metal oxide based pH sensors are used in various applications, especially when the conventional glass electrode is unsuitable due to its fragility or when the applications require disposable sensors, e.g. for biomedical, clinical or food process monitoring. Generally, such pH sensors are produced by thermal oxidation or electrochemical deposition, neither suited for mass production nor miniaturization. Herein, we report on the fabrication of reliable and sensitive pH sensors based on the nano-assembly of iridium oxide (IrO x ) nanoparticles and polydiallyldimethylammonium (PDDA) polymer layers. Such potentiometric sensors were very reproducibly fabricated on a large-scale via a layer-by-layer inkjet printing (LbL IJP) methodology. The obtained results indicated the ability of the LbL IJP technique to easily manipulate the NP coverage by the number of printed bilayers, leading to a swift sensor optimization. Open-circuit potentials were recorded to evaluate the pH sensitivity, response time, and reproducibility of the pH electrodes, which exhibit a rapid, linear and near-Nernstian pH response of about 59 mV/pH. Moreover, an RSD of 0.6% for five different electrodes from the same printing batch showed the excellent reproducibility of the IJP process with a correlation coefficient of 0.99 for all measurements. The insights gained in this study could be the basis for a new approach of developing scalable, patterned and flexible pH sensors with improved performance and a wide range of applications. [ABSTRACT FROM AUTHOR]

Iridium(IV) oxide nanoparticles were facilely prepared from iridium trichloride hydrate and sodium hydroxide by a ball-milling reaction at room temperature. The 'naked' iridium nanocatalyst showed high stability and activity for the hydrogenation of a series of nitrogen heterocycles, for the first time, under a hydrogen balloon at room temperature with a selectivity of higher than 99%. Besides, an unprecedented substitution-dependent effect was discovered, where substrates with vicinal substituents on 2-, 3-, or 8-positions exhibited distinctly higher reaction rates than unsubstituted or remote substituted ones. Extraordinary recyclability was discovered in the hydrogenation of 2-methylquinoline for 30 runs without loss of activity. [ABSTRACT FROM AUTHOR]

In this work, a novel biosensor based on electrochemically reduced graphene oxide and iridium oxide nanoparticles for the detection of angiotensin-converting enzyme inhibitor drug, captopril, is presented. For the preparation of the biosensor, tyrosinase is immobilized onto screen printed electrode by using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-Hydroxysuccinimide coupling reagents, in electrochemically reduced graphene oxide and iridium oxide nanoparticles matrix. Biosensor response is characterized towards catechol, in terms of graphene oxide concentration, number of cycles to reduce graphene oxide, volume of iridium oxide nanoparticles and tyrosinase solution. The designed biosensor is used to inhibit tyrosinase activity by Captopril, which is generally used to treat congestive heart failure. It is an angiotensin-converting enzyme inhibitor that operates via chelating copper at the active site of tyrosinase and thioquinone formation. The captopril detections using both inhibition ways are very sensitive with low limits of detection: 0.019 µM and 0.008 µM for chelating copper at the active site of tyrosinase and thioquinone formation, respectively. The proposed methods have been successfully applied in captopril determination in spiked human serum and pharmaceutical dosage forms with acceptable recovery values. [ABSTRACT FROM AUTHOR]

A methimazole (MT) biosensor based on a nanocomposite of magnetic nanoparticles (MNPs) functionalized with iridium oxide nanoparticles (IrOx NPs) and tyrosinase (Tyr) immobilized onto screen printed electrode (SPE) by using a permanent magnet is presented. This system is evaluated in batch mode via chelating copper at the active site of tyrosinase and in flow mode by thioquinone formation. The MT detection in flow mode is achieved using a hybrid polydimethylsiloxane/polyester amperometric lab-on-a-chip (LOC) microsystem with an integrated SPE. Both systems are very sensitive with low limit of detection (LOD): 0.006 μM and 0.004 μM for batch and flow modes, respectively. Nevertheless, the flow mode has advantages such as its reusability, automation, low sample volume (6 μL), and fast response (20 s). Optimization and validation parameters such as enzyme–substrate amount, flow rate, inhibition conditions, repeatability and reproducibility of the biosensor have been performed. The proposed methods have been applied in MT detection in spiked human serum and pharmaceutical dosage forms. [ABSTRACT FROM AUTHOR]

Iridium oxide nanoparticles (IrO2 NPs) synthesized following a previously reported chemical route are presented as novel tags for immunosensing taking advantage of their electrocatalytic activity towards water oxidation reaction (WOR). Cyclic voltammetry and chronoamperometry for the evaluation of the IrO2 NPs electrocatalytic activity towards WOR at neutral pH were used. The chronoamperometric current recorded at a fixed potential of +1.3 V constituted the analytical signal allowing the quantification of IrO2 NPs at nM levels. Modification of the surface of citrate-capped IrO2 NPs with anti-Apolipoprotein E antibodies (αApoE) was successfully achieved and the as-prepared conjugates were used for the electrocatalytic detection of ApoE Alzheimer disease (AD) biomarker in a magnetosandwich immunoassay, reaching a detection limit of 68 ng/mL. Human plasma of a patient suffering AD was also evaluated, estimating an ApoE concentration of 20 µg/mL which is in concordance with the obtained in previously reported approaches. This novel IrO2 NPs based electrocatalytic assay presents the advantage of the signal generation in the same medium where the immunoassay takes place (PBS, pH 7.4) avoiding the use of additional reagents which also opens the way to future integrated biosensing systems and platforms with interest for other proteins as well as DNA and cells analysis. [ABSTRACT FROM AUTHOR]

• Periodic amplification strategies of DNA mimicking enzymes were employed. • High sensitivity for microRNA detection in vitro. • Clear imaging of microRNA in living cells. • pH-regulated automatic drug delivery system. • The dual functions of photothermal therapy and chemotherapy are combined in one. A novel iridium oxide nanoparticles-based probe was developed for in vivo fluorescence imaging of microRNA and synergistic chem/photothermal treatments of tumor. The theranostic nanoprobe was constructed by functionizing iridium oxide nanoparticles with split DNAzyme precursor and chemotherapeutic agent doxorubicin. The split DNAzyme precursor was used for specifically recognizing the target microRNA in cancer cells and then releasing the preloaded fluorescence for detection through DNAzyme cleavage reaction. Because the fluorescence was enhanced by cycle amplification process, the nanoprobe exhibited high sensitivity in the cell-free test. Both in vitro and in vivo fluorescence imaging studies proved the specificity and feasibility of the nanoprobe in tumor imaging. In order to enhance the effectiveness of cancer cell therapy, synergistic chem/photothermal treatments were designed on the nanoprobe. Based on the photothermally controlled drug release and chemotherapeutic treatment of doxorubicin, and the photothermal effect of iridium oxide nanoparticles, the nanoprobe exhibited excellent synergy effect on cancer cell treatment under near-infrared irradiation. In particular, in vivo therapeutic studies proved a great inhibition of the tumor growth. Therefore, this work provided a promising theranostic nanoprobe for both tumor imaging and synergistic treatment of cancer cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A water oxidation catalyst with two separate active centers. • IrO 2 nanoparticle immobilized-monodisperse-porous CeO 2 microspheres. • Monodisperse-porous CeO 2 microspheres both as an active center and a support. • Multiple oxidation states of cerium for oxygen vacancies in CeO 2 microspheres. • Enhanced activity due to individual activities of IrO 2 and CeO 2 components. • Superior catalytic activity with respect to catalysts containing inertial supports. Iridium oxide nanoparticle (IrO 2 NP) decorated-monodisperse, porous CeO 2 (IrO 2 @CeO 2) microspheres were synthesized as a heterogeneous catalyst for chemical water oxidation with cerium ammonium nitrate (CAN) or sodium periodate (NaIO 4) as the sacrificial agent. Before synthesis of the proposed catalyst, considerable oxygen evolution was observed using only plain CeO 2 microspheres as the catalyst. Individual catalytic activity of plain CeO 2 microspheres was explained by the formation of oxidative oxygen species due to the coexistence of Ce(III) and Ce(IV) ions on the surface as demonstrated by deconvoluted XPS analysis. Hence, CeO 2 component of IrO 2 @CeO 2 microspheres acted either support or active center. In other words, another active center, IrO 2 NPs, was immobilized on the satisfactorily high surface area of porous CeO 2 microspheres acted a support. IrO 2 @CeO 2 microspheres with double catalytic active centers exhibited superior catalytic activity with respect to IrO 2 NP decorated-porous SiO 2 (IrO 2 @SiO 2) microspheres due to the contribution coming from CeO 2 microspheres. The maximum turnover number (TON) and turnover frequency (TOF) were obtained as 483 and 724 h−1 using CAN. By using IrO 2 @CeO 2 microspheres as the catalyst, no significant decrease occurred in the oxygen evolution in the repeated runs with NaIO 4 as the oxidant while the oxygen evolution apparently decreased using CAN. [ABSTRACT FROM AUTHOR]

Salbutamol (SAL), a β-2 adrenoreceptor agonist, is an unpopular addition to livestock and poultry, causing several side effects to human health. Thus, it is very important to develop a simple and rapid analytical method to screen SAL in the field of food safety. Here, we present an immunochromatographic assay (ICA) method for sensitively detecting SAL with polydopamine-decorated iridium oxide nanoparticles (IrO 2 @PDA NPs) as a signal tag. The IrO 2 @PDA with excellent hydrophilicity, biocompatibility, and stability was synthesized by oxidating self-polymerization of dopamine hydrochloride (DAH) on the surface of IrO 2 NPs and used to label monoclonal antibodies (mAbs) through simple physical adsorption. Compared with IrO 2 NPs, the IrO 2 @PDA also possessed superior optical properties and higher affinity with mAbs. With the proposed method, the limit of detection for SAL was 0.002 ng/mL, which was improved at least 24-fold and 180-fold compared with the IrO 2 NPs-based ICA and conventional gold nanoparticles-based ICA, respectively. Furthermore, the SAL residuals in pork, pork liver, and beef were successfully detected by the developed biosensor and the recoveries ranged from 85.56% to 115.56%. Briefly, this work indicated that the powerful IrO 2 @PDA-based ICA can significantly improve detection sensitivity and has huge potential for accurate and sensitive detection of harmful small molecules analytes in food safety fields.

Efficient OER Catalysts: Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony-Doped Tin Oxide Support (Adv. Funct. Keywords: antimony-doped tin oxide microparticles; homogenous iridium coating; iridium oxide nanoparticles; supported OER catalyst; ultrasonic spray pyrolysis Antimony-doped tin oxide microparticles, homogenous iridium coating, iridium oxide nanoparticles, supported OER catalyst, ultrasonic spray pyrolysis. [Extracted from the article]

A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open‐porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO‐supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO‐supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr−1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2‐supported IrO2 reference catalyst under the same measurement conditions. [ABSTRACT FROM AUTHOR]

The unusually high tolerance toward chemical functional groups of the copper(I)-catalyzed Huisgen-Sharpless-Meldal 1,3-dipolar cycloaddition of azides and alkynes protocol (the CuAAC or "click" reaction) associated with its mild conditions and high yields has been explored in the present methodology to successfully prepare water oxidation catalyst iridium oxide nanoparticles decorated with organic dyes. The "click reaction" has proven to be an excellent synthetic tool to overcome the incompatible solubility of the hydrophilic iridium oxide nanoparticles and the hydrophobic dyes. A complex artificial photosynthetic model designed to mimic the photoinduced redox processes occurring in photosystem II is used as a hydrophobic dye to highlight the efficiency and selectiveness of the method.