Search Results (44)

Industrial catalysts are accelerating the global transition toward renewable energy, serving as enablers for innovative technologies that enhance efficiency, lower costs, and improve environmental sustainability. This review explores the pivotal roles of industrial catalysts in hydrogen production, biofuel generation, and biomass conversion, highlighting their transformative impact on renewable energy systems. Precious-metal-based electrocatalysts such as ruthenium (Ru), iridium (Ir), and platinum (Pt) demonstrate high efficiency but face challenges due to their cost and stability. Alternatives like nickel-cobalt oxide (NiCo₂O₄) and Ti₃C₂ MXene materials show promise in addressing these limitations, enabling cost-effective and scalable hydrogen production. Additionally, nickel-based catalysts supported on alumina optimize SMR, reducing coke formation and improving efficiency. In biofuel production, heterogeneous catalysts play a crucial role in converting biomass into valuable fuels. Co-based bimetallic catalysts enhance hydrodeoxygenation (HDO) processes, improving the yield of biofuels like dimethylfuran (DMF) and γ-valerolactone (GVL). Innovative materials such as biochar, red mud, and metal–organic frameworks (MOFs) facilitate sustainable waste-to-fuel conversion and biodiesel production, offering environmental and economic benefits. Power-to-X technologies, which convert renewable electricity into chemical energy carriers like hydrogen and synthetic fuels, rely on advanced catalysts to improve reaction rates, selectivity, and energy efficiency. Innovations in non-precious metal catalysts, nanostructured materials, and defect-engineered catalysts provide solutions for sustainable energy systems. These advancements promise to enhance efficiency, reduce environmental footprints, and ensure the viability of renewable energy technologies. Full article

This work investigates photoactive inorganic powders (SiO₂, IrSiO₂, and IrO₂/IrSiO₂) and their derivatives modified with metallated porphyrin, focusing on their ability to generate reactive oxygen species (ROS) under visible light exposure. The core material, SiO₂, exhibits a tubular morphology and a high density of optically active defects. Modifiers such as metallic and iridium oxide nanoparticles, along with porphyrin, are employed to enhance light absorption and the generation of singlet oxygen (¹O₂) for potential biomedical applications. The time-dependent photogeneration of singlet oxygen is monitored using a Singlet Oxygen Green Sensor (SOSG), and its reactivity is evaluated in relation to DL α-Tocopherol through a spectrofluorimetric analysis. The photoactive materials, both before and after porphyrin modification, are characterized using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), UV–Vis Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), N₂ adsorption–desorption measurements, and zeta potential measurements. Full article

Catalytic activity, mechanisms, and active sites were determined for methane steam reforming (MSR) over gadolinium-doped ceria (GDC) supported iridium (0.1 wt%) prepared by impregnation of GDC with iridium acetylacetonate. Isothermal steady-state rate measurements followed by micro-gas chromatography analysis were performed at 660 and 760 °C over Ir/GDC samples pretreated in N₂ or H₂ at 900 °C. Transient responses to CH₄ or H₂O step changes in isothermal conditions were carried out at 750 °C over Ir/GDC pretreated in He or H₂ using online quadrupole mass spectrometry. In the proposed mechanism, Ir/GDC proceeds through a dual-type active site associating, as follows: (i) Ir metallic particles surface as active sites for the cracking of CH₄ into reactive C species, and (ii) reducible (Ce⁴⁺) sites at GDC surface responsible for a redox mechanism involving Ce⁴⁺/Ce³⁺ sites, being reduced by reaction with reactive C into CO (or CO₂) depending on the oxidation state of GDC and re-oxidized by H₂O. Full reduction of reducible oxygen species is possible with CH₄ after He treatment, whereas only 80% is reached in CH₄ after H₂ treatment. Full article

This study investigated the electronic structure of single-atom Rhodium (Rh) and Iridium (Ir) adsorbed on defective and impurity-doped ZnO(0001) surfaces, and assessed their activity towards the CO oxidation reaction. Our findings reveal that surface impurities significantly influence the binding energies and electronic properties of the metal atoms, with Al and Cr serving as particularly effective promoters. While Rh and Ir acquire a positive charge upon incorporation on the unpromoted Zn(0001) surface, adsorption directly on the promoter results in a net negative charge, thus facilitating the activation of both CO and O₂ species. These results highlight the potential of impurity-promoted ZnO surfaces in modulating and tailoring the electronic properties of SACs, which can be used for a rational design of active single-atom catalysts. Full article

In the search of sustainable energy solutions, proton exchange membrane water electrolyzers (PEMWEs) have emerged as a promising alternative for sustainable clean hydrogen production. This study focuses on synthesis and characterization of Ruthenium (Ru)-modified iridium oxide (IrO₂) catalysts. The anode is the principal reason for the high overpotential of PEMWEs and it also greatly increases the cost of the electrolyzers. IrO₂ is highly stable and corrosion-resistant, particularly in acidic environments, making it a durable catalyst for the oxygen evolution reaction (OER) in PEMWEs, though it suffers from a relatively high overpotential. Ruthenium oxide (RuO₂), on the other hand, is more catalytically active with a lower overpotential, but is less stable under the same conditions. In this study, the goal was to improve the catalytic activity and stability of the anode catalyst, IrO₂, through the controlled incorporation of Ru and to reduce overall catalyst cost due to the reduced iridium content. This synergistic combination allows for better performance in terms of conductivity, efficiency, and durability, making Ru-modified IrO₂ an ideal catalyst for OER in PEMWE applications. The Adams fusion method was adapted and used to synthesize the catalysts. The modified catalysts were characterized using analytical instruments. These analyses provided insights into the structural, morphological, and electrochemical properties of the Ru-modified IrO₂ catalysts. Full article

For square-planar late transition metal pyridine, diimine (Rh, Ir) complexes with hydro-xido, methoxido, and thiolato ligands. We could previously establish sizable metal-O- and S π-bonding interactions. Herein, we report the hydrogenation studies of iridium hydroxido and methoxido complexes, which quantitatively lead to the trihydride compound and water/methanol. The iridium trihydride displays a highly fluctional structure with scrambling hydrogen atoms, which can be described as a dihydrogen hydride system based on NMR and DFT investigations. This contrasts the iridium sulfur compounds, which are not reacting with dihydrogen. According to DFT and LNO-CCSD(T) calculations, hydrogenation of the methoxido complex proceeds by a two-step mechanism, i.e., an oxidative addition step of H₂ to an Ir(III) dihydride intermediate with consecutive reductive O-H elimination of methanol. Based on PNO-CCSD(T) calculations, the reactivity difference between the O- and S-donors can be traced to the stronger H-O bonds in the water/methanol products compared to the S-H bonds in the sulphur congeners, which serves as a driving force for hydrogenation. Full article

Electrochemical water splitting, a sustainable method for hydrogen production, faces the challenge of slow oxygen evolution reaction (OER) kinetics. Iridium oxide (IrO₂) is widely regarded as the most effective catalyst for OER due to its excellent properties. Compared to nanoparticles, IrO₂ thin films exhibit significant advantages in OER, including a uniform and stable catalytic interface and excellent mechanical strength. This paper reviews recent advancements in one-step deposition techniques for the preparation of IrO₂ thin films and their application in OER. Additionally, it analyzes the advantages and disadvantages of various methods and the latest research achievements, and briefly outlines the future trends and applications. Full article

Electrochemical pH sensors have a wide range of industrial applications such as in medicine due to their fast response and high sensitivity to pH changes. This work focuses on the preparation of samples based on the nanostructure of TiO₂ with potentiostatically deposited particles of iridium and its oxides (IrO₂), using a Ti-6Al-4V alloy as the base material, and subsequent surface characterization. Transmission electron microscopy and secondary ion mass spectroscopy showed Ir particles distributed in the nanotubes. Using a potentiostatic method, a stable pH sensor was prepared. By monitoring the open circuit potential, it was shown that this sensor is usable even without being kept in a storage medium and does not react to changes in the redox potential of the solution. Full article

Preparing high-performance oxygen evolution reaction (OER) catalysts with low precious metal loadings for water electrolysis applications (e.g., for green hydrogen production) is challenging and requires electrically conductive, high-surface-area, and stable support materials. Combining the properties of stable TiO₂ with those of active iridium oxide, we synthesized highly active electrodes for OER in acidic media. TiO₂ powders (both commercially available Degussa P-25^® and hydrothermally prepared in the laboratory from TiOSO₄, either as received/prepared or following ammonolysis to be converted to titania black), were decorated with IrO₂ by UV photodeposition from Ir(III) aqueous solutions of varied methanol scavenger concentrations. TEM, EDS, FESEM, XPS, and XRD measurements demonstrate that the optimized version of the photodeposition preparation method (i.e., with no added methanol) leads to direct deposition of well-dispersed IrO₂ nanoparticles. The electroactive surface area and electrocatalytic performance towards OER of these catalysts have been evaluated by cyclic voltammetry (CV), Linear Sweep Voltammetry (LSV), and Electrochemical Impedance Spectroscopy (EIS) in 0.1 M HClO₄ solutions. All TiO₂-based catalysts exhibited better mass-specific (as well as intrinsic) OER activity than commercial unsupported IrO₂, with the best of them (IrO₂ on Degussa P-25^® ΤiO₂ and laboratory-made TiO₂ black) showing 100 mAmg_Ir⁻¹ at an overpotential of η = 243 mV. Chronoamperometry (CA) experiments also proved good medium-term stability of the optimum IrO₂/TiO₂ electrodes during OER. Full article

Two series of bimetallic photocatalysts (0.5% Pt/0.01–0.5% IrO_x/g-C₃N₄ and 0.1% Pt/0.01–0.1% IrO_x/g-C₃N₄) were synthesized by the thermolysis of melamine cyanurate and a successive deposition of platinum and iridium labile complexes (Me₄N)₂[Pt₂(μ-OH)₂(NO₃)₈] and fac-[Ir(H₂O)₃(NO₂)₃. The synthesized photocatalysts were studied by a set of physicochemical analysis techniques. Platinum exists in two states, with up to 60% in metallic form and the rest in the Pt²⁺ state, while iridium is primarily oxidized to the Ir³⁺ state, which was determined by X-ray photoelectron spectroscopy (XPS). The specific surface area (S_BET), which is determined by low-temperature nitrogen adsorption, ranges from 80 to 100 m² g⁻¹ and the band gap energy (E_g) value is in the range of 2.75–2.80 eV as found by diffuse reflectance spectroscopy (DRS). The activity of the photocatalysts was tested in the photocatalytic production of hydrogen from ultrapure water under visible light (λ = 400 nm). It was found that the splitting of water occurs with the formation of the stochiometric amount of H₂O₂ as an oxidation product. Two photocatalysts 0.5% Pt/0.01% IrO_x/g-C₃N₄ and 0.1% Pt/0.01% IrO_x/g-C₃N₄ showed the highest activity at 100 μmol h⁻¹ g_cat⁻¹, which is among the highest in H₂ production published for such systems. Full article

Electrodeposited amorphous hydrated iridium oxide (IrOx) is a promising material for pH sensing due to its high sensitivity and the ease of fabrication. However, durability and variability continue to restrict the sensor’s effectiveness. Variation in probe films can be seen in both performance and fabrication, but it has been found that performance variation can be controlled with potentiostatic conditioning (PC). To make proper use of this technique, the morphological and chemical changes affecting the conditioning process must be understood. Here, a thorough study of this material, after undergoing PC in a pH-sensing-relevant potential regime, was conducted by voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Fitting of XPS data was performed, guided by raw trends in survey scans, core orbitals, and valence spectra, both XPS and UPS. The findings indicate that the PC process can repeatably control and conform performance and surface bonding to desired calibrations and distributions, respectively; PC was able to reduce sensitivity and offset ranges to as low as ±0.7 mV/pH and ±0.008 V, respectively, and repeat bonding distributions over ~2 months of sample preparation. Both Ir/O atomic ratios (shifting from 4:1 to over 4.5:1) and fitted components assigned hydroxide or oxide states based on the literature (low-voltage spectra being almost entirely with suggested hydroxide components, and high-voltage spectra almost entirely with suggested oxide components) trend across the polarization range. Self-consistent valence, core orbital, and survey quantitative trends point to a likely mechanism of ligand conversion from hydroxide to oxide, suggesting that the conditioning process enforces specific state mixtures that include both theoretical Ir(III) and Ir(IV) species, and raising the conditioning potential alters the surface species from an assumed mixture of Ir species to more oxidized Ir species. Full article

The syntheses of new neutral square-planar pyridine di-imine rhodium and iridium complexes with O- and S-donor (OH, OR, SH, SMe and SPh) ligands along with analogous cationic compounds are reported. Their crystal and electronic structures are investigated in detail with a focus on the non-innocence/innocence of the PDI ligand. The oxidation states of the metal centers were analyzed by a variety of experimental (XPS and XAS) and theoretical (LOBA, EOS and OSLO) methods. The dπ-pπ interaction between the metal centers and the π-donor ligands was investigated by theoretical methods and revealed the partial multiple-bond character of the M-O,S bonds. Experimental support is provided by a sizable barrier for the rotation about the Ir-S bond in the methyl thiolato complex and confirmed by DFT and LNO-CCSD(T) calculations. This was corroborated by the high Ir-O and Ir-S bond dissociation enthalpies calculated at the PNO-CCSD(T) level. Full article

The increasing use of natural gas as an efficient, reliable, affordable, and cleaner energy source, compared with other fossil fuels, has brought the catalytic CH₄ complete oxidation reaction into the spotlight as a simple and economic way to control the amount of unconverted methane escaping into the atmosphere. CH₄ emissions are a major contributor to the ‘greenhouse effect’, and therefore, they need to be effectively reduced. Catalytic CH₄ oxidation is a promising method that can be used for this purpose. Detailed studies of the activity, oxidative thermal aging, and the time-on-stream (TOS) stability of pristine La_1−xSr_xMnO₃ perovskites (LS_XM; X = % substitution of La with Sr = 0, 30, 50 and 70%) and iridium-loaded Ir/La_1−xSr_xMnO₃ (Ir/LS_XM) perovskite catalysts were conducted in a temperature range of 400–970 °C to achieve complete methane oxidation under excess oxygen (lean) conditions. The effect of X on the properties of the perovskites, and thus, their catalytic performance during heating/cooling cycles, was studied using samples that were subjected to various pretreatment conditions in order to gain an in-depth understanding of the structure–activity/stability correlations. Large (up to ca. 300 °C in terms of T₅₀) inverted volcano-type differences in catalytic activity were found as a function of X, with the most active catalysts being those where X = 0%, and the least active were those where X = 50%. Inverse hysteresis phenomena (steady-state rate multiplicities) were revealed in heating/cooling cycles under reaction conditions, the occurrence of which was found to depend strongly on the employed catalyst pre-treatment (pre-reduction or pre-oxidation), while their shape and the loop amplitude were found to depend on X and the presence of Ir. All findings were consistently interpreted, which involved a two-term mechanistic model that utilized the synergy of Eley–Rideal and Mars–van Krevelen kinetics. Full article

We have assessed new anodic coloring materials that can be used as ion storage layers in complementary energy storage electrochromic devices (ESECDs) to enhance their electrochromic storage performance. In our study, we fabricated counter electrodes (ion storage layers) using an IrO₂-doping NiO (Ir:NiO) film through cathodic arc plasma (CAP) with varying surface charge capacities. We have also investigated the influence of a MoO₃-doped WO₃ (Mo:WO₃) film using various Ar/O₂ gas flow ratios (1/4, 1/5, and 1/6, respectively). The ESECDs used in the demonstration were 10 × 10 cm² in size and achieved an optical transmittance modulation of the Ir:NiO ESECDs (glass/ITO/ Mo:WO₃/gel polymer electrolytes/ Ir:NiO/ITO/glass), with ΔT = 53.3% (from T_bleaching (66.6%) to T_coloration (13.1%)). The ESECDs had a quick coloration time of 3.58 s, a rapid bleaching time of 1.24 s, and a high cycling durability. Furthermore, it remained at a 45% transmittance modulation level even after 3000 cycles. New anodic materials can thereby provide an alternative to traditional active materials for bi-functional electrochromic batteries. Full article

An experimental study of the phase equilibria of the Ho-rich part of the Ho-Ir-O ternary system at 1073 K by means of x-ray diffraction, differential scanning calorimetry, and scanning electron microscopy has been carried out. Ho-hcp and four binary compounds, namely Ho₃Ir, Ho₅Ir₂, Ho₅Ir₃, and Ho₂O₃, were identified in the Ho-Ir-O model alloys after long-term annealing (350–1220 h). No solubility of iridium in Ho₂O₃ oxide and Ho-hcp was observed. No ternary phase was found. Based on the experimental results, an isothermal section of the Ho-rich part of the Ho-Ir-O system at 1073 K was constructed. In addition, the microstructure of as-cast alloys was studied. An irregular eutectic consisting of faceted Ho-phase in Ho₃Ir phase was observed in the alloys with Ho-hcp + Ho₃Ir + Ho₂O₃ phase composition, and the temperature of the eutectic reaction Ho-hcp + Ho₃Ir ↔ liquid was determined. Full article