Iridium Content Research Articles

Investigation of the iridium adsorption process with functionalized magnetic nanoparticles using triisobutylphosphine sulfide extractors

In this research work, the adsorption process of iridium using magnetic nanoparticles functionalized with Cyanex 471X has been investigated. In this regard, parameters affecting the adsorption process such as pH, initial concentration of iridium ions, contact time and adsorbent dosage were assessed. According to the results, pH 6, adsorbent dosage 1.2 g/L, initial concentration of iridium of 10 mg/L, and contact time of 10 min were selected as optimal conditions for iridium adsorption by this synthesized magnetic nanosorbent. The kinetics of the adsorption process was studied, and it was found that the adsorption reaction follows the pseudo-second-order kinetic model with the correlation coefficient of 0.9960. Also, experimental studies indicated that the Langmuir adsorption isotherm model best matches the experimental data (R2 = 0.9961). The maximum adsorption capacity of the nanosorbent for iridium adsorption was estimated to be 35.34 mg/g by the Langmuir isotherm. With the thermodynamic analysis of the adsorption process, it was found that this process is endothermic and spontaneous. In addition, in the investigation of iridium adsorption and desorption, HCl/HNO3 solution with a concentration of 1.5 M was selected as suitable eluent.

Controlled Defective Engineering on CuIr Catalyst Promotes Nitrate Selective Reduction to Ammonia.

Electrochemical nitrate reduction reaction (NO3-RR) is a promising low-carbon and environmentally friendly approach for the production of ammonia (NH3). Herein, we develop a high-temperature quenched copper (Cu) catalyst with the aim of inducing nonequilibrium phase transformation, revealing the multiple defects (distortion, dislocations, vacancies, etc.) presented in Cu, which lead to low overpotential for NO3-RR and high efficiency for NH3 production. Further loading a low content of iridium (Ir) species on the Cu surface improves the reactivity and ammonia selectivity. The resultant CuIr electrode exhibits a Faradaic efficiency of 93% and a record yield of 6.01 mmol h-1 cm-2 at -0.22 VRHE exceeding those of state-of-the-art NO3-RR catalysts. Detailed investigations have demonstrated that the synergistic effect between multiple defects and Ir decoration effectively regulate the d-band center of copper, change the adsorption state of the catalyst surface, and promote the adsorption and reduction of intermediates and reactants. The strong H* adsorption ability of the Ir element provides more active hydrogen for the generation of ammonia, promoting the reduction of nitrate to NH3.

Chemical Epitaxy of Iridium Oxide on Tin Oxide Enhances Stability of Supported OER Catalyst.

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 IrO2 is achieved on the isostructural support material SnO2, both of which have a rutile structure with very similar lattice constants. Crystallization of amorphous IrOx on an SnO2 substrate results in interconnected, ultrasmall IrO2 crystallites that grow along the surface and are firmly anchored to the substrate. Thereby, the IrO2 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.

Low Ir-Containing Materials As Anode Catalysts for PEM Water Electrolysis

The PEM electrolysis is based on the application of IrO2 as anode catalyst. Until now, there is no real alternative for this electrocatalyst, since the highly acidic and oxidative conditions at the anode lead to rapid corrosion.[1-3] With steadily increasing energy consumption, the demand for iridium will exceed the available resources in a few decades. As a result, the price of iridium as well as the technologies based on it will continuously increase. An enhancement of PEM electrolysis capacities on a large scale can therefore only be realized in the long term if the application of iridium is significantly reduced.[4] Therefore, our research aims at reducing the iridium content of PEM anodes while maintaining catalytic activity and stability.In this work, two approaches to save iridium were applied. On the one hand the iridium content was reduced by supporting it, on the other hand an additional, readily available metal is incorporated that is protected from corrosion by the presence of iridium and at the same time assists the iridium in catalysis.So, bimetallic included low-loading Ir and different transition metal (Ru, Sn, and Ag) nanoparticles on titanium nitride (TiN) were synthesized by using a chemical reduction method and thermal treatment. Experimentally, a IrSnOx/TiN sample in 0.5 M H2SO4 with an Ir loading of 0.05 mgIr/cm2 achieves a mass activity of over 450 A/gIr at 1.6 V vs RHE and an overpotential of 297 mV at 10 mA/cm2. The investigation includes stability tests at constant current density of 10 mA/cm2 and determination of impedance by electrochemical impedance spectroscopy (EIS).As result, a suitable anode material was successfully achieved, which exhibits a similarly good activity and stability values compared to the IrO2 materials that have been used industrially so far, but with a significantly reduction of iridium to 24% of the usually applied amount.[1] C. Minke, M. Suermann, B. Bensmann, R.H. Rauschenbach, Int. J. Hydrog. Energy, 2021, 46, 23581-23590.[2] F. Scarpelli, N. Godbert, A. Crispini, I. Aiello, Inorganics, 2022, 10, 115.[3] J. Gao, Y. Liu, B. Liu, K.W. Huang, ACS Nano, 2022, 16, 17761-17777.[4] T. Reier, H. N. Nong, D. Teschner, R. Schlögl, P. Strasser, Adv. Energy Mater., 2017, 7, 1601275.

Iridium-Based Electrocatalysts for Oxygen Evolution Reaction in Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) show the fast response to a wide electrical load range, making them compatible to couple with intermittent renewable energy systems such as wind and solar power. However, the low efficiency, instability, and high cost of anodic electrocatalysts for the oxygen evolution reaction (OER) severely hinder the widespread deployment of PEMWEs. Hitherto, iridium-based catalysts still play an irreplaceable role for their trade-off catalytic activity and stability. To meet the scarcity of iridium, reducing the iridium loading and designing low iridium-based electrocatalysts have become the mainstream. Particularly, perovskite-type oxides possess flexible compositions, enabling them ideal material platform for the optimization of catalytic performance. In this work, several materials of iridium-based perovskite-type oxides were acquired by coupling iridium with various transition elements in B-site and regulating A-site cations, which both diluted the usage of iridium and utilized the multi-metallic synergistic effect to achieve high activity and stability. Evolution of the surface structure was monitored by in-situ Raman spectroscopy to identify the active site and to uncover the catalytic mechanism. Besides, density functional theory (DFT) calculation was used as an auxiliary tool to analyze the local structure and electrochemical behavior of the electrode surface for its cost-effectiveness. Furthermore, membrane electrode assembly (MEA) based on the optimum composition was assembled to evaluate the performance of novel electrocatalysts for PEMWEs. Results of this work provide a new perspective of designing low iridium content electrocatalysts for OER in PEMWEs. Acknowledgement This work is funded by the National Natural Science Foundation of China (No. 22002089, 52072239).

Photodeposition-Based Synthesis of TiO2@IrOx Core-Shell Catalyst for Proton Exchange Membrane Water Electrolysis with Low Iridium Loading.

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core-shell catalyst with a reduced iridium content as low as 40wt.% is presented. Using this synthesis method, titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1±0.4nm are obtained. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core-shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. It is demonstrated that the novel TiO2@IrOx core-shell catalyst clearly outperforms the commercial reference in single-cell tests with an iridium loading below 0.3mgIrcm-2 exhibiting a superior iridium-specific power density of 17.9kW gIr -1 compared to 10.4kW gIr -1 for the commercial reference.

In situ transformation from metal-organic framework into iridium-iron hollow hexagonal rod to promote oxygen evolution reaction

Developing highly efficient and durable electrocatalysts for water oxidation in alkaline media is crucial for hydrogen production in industrialization. IrO2 is a highly promising electrocatalyst for oxygen evolution reaction (OER), but its large-scale is still limited to the sluggish OER kinetics in alkaline solution due to the multi-steps adsorption of -OH and H2O. Herein, we reported a novel in-situ generation from metal-organic framework strategy for preparing hollow hexagonal rod IrFex electrocatalysts (IrFex HHRs). Specifically, the optimized IrFe3 HHRs shows an excellent OER electrocatalytic activity, including low overpotential of 265, 295 and 307 mV at the current density of 10, 50 and 100 mA cm−2, and high stability (100 h). The experimental results revealed that the existent interfacial Fe-O-Ir bonds between Ir and MIL-88A (Fe) can promote electrons transport to improve the electrocatalyst activity. This work represents a new strategy for designing an efficiency electrocatalysts with low iridium content derived from Ir doped-bimetal MOF material.

A low iridium content greatly improves the peroxidase-like activity of noble metal nanozymes for sensitive colorimetric detection.

The enzyme-like activity of noble metal nanomaterials has been widely demonstrated. However, as an important noble metal, iridium (Ir) and its alloy nanomaterials have been less studied, particularly regarding the effect of Ir content on enzyme-like activity. Here, we demonstrated for the first time that a low Ir content can greatly improve the peroxidase-like activity of Pt-based nanozymes. When the weight percentage of Ir was 3.45% in trimetallic PtAuIr hollow nanorods (HNRs) and 2.86% in bimetallic PtIr HNRs, their specific activity increased by approximately 70% compared to their PtAu and Pt counterparts, respectively. However, a slightly higher percentage of Ir significantly diminished the enhancement effect on their specific activity. Density functional theory (DFT) calculations show that the rate-determining step (RDS) energy barrier of the nanozyme with low Ir content is lower than that of the nanozyme with slightly higher Ir content. Furthermore, we studied the kinetic properties of the PtAuIr nanozyme using TMB as the substrate. Its Michaelis-Menten constant (Km) and Vmax were 1.756 mM and 2.152 × 10-6 M s-1, respectively. Additionally, a colorimetric detection platform based on the PtAuIr nanozyme was established and applied to detect o-phenylenediamine (OPD), with a detection limit as low as 0.076 μM. This study highlights the important role of the Ir content in Pt-based nanozymes and demonstrates that PtAuIr nanozymes have potential applications in environmental detection.

Improvement of chlorine evolution stability and activity of RuO2-TiO2/IrO2-Ta2O5 electrode with low iridium content by alternating coating thermal decomposition method

Electrochemical chlorine evolution reaction (CER) is an important electrochemical reaction for industrial application, but it has serious problems such as the short service life and low electrolytic efficiency in the...

Supported Iridium Catalysts for Water Electrolysers

It is essential to reduce iridium in water electrolysers without compromising performance to lower the cost of green hydrogen. One strategy often used in catalysis to reduce precious metal catalyst usage is to deposit catalysts on high surface area supports. However, the catalyst supports need to be stable under the reaction conditions and also economically viable. Additionally, the catalyst-support moieties need to be sufficiently conductive. In this project, we explore platinum coated titanium dioxide as supports for iridium catalysts. Platinum is necessary to improve conductivity of the support motifs. Without this conductive platinum layer, extremely high (75 wt%) iridium loadings are needed to prepare commercially viable supported iridium catalysts.1, 2 In this work we synthesise and characterise a systematic series of catalysts whereby the Pt loading is varied in order to understand the loading effect on conductivity, and thus, electrocatalytic activities and durabilities.Previously, we have demonstrated the efficacy of a Pt conductive layer as an effective strategy for boosting the mass activity of Iridium in a half-cell configuration.4 However, translating the performance, more critically durability, in a device remained to be demonstrated. Here, we also begin by rapidly assessing the electrochemical performance of the library of prepared catalysts in a half-cell configuration (rotating disk electrodes, RDEs). Subsequently, catalysts that show promising activity and durability in half-cell are integrated into a PEM electrolyser. This approach is economic and efficient since integrating catalysts into membrane electrode assemblies and running electrolyser tests are resource and time intensive. However, there are challenges associated with replicating activity and durability from half-cell to device performance.3 Thus, we also explore methodologies and strategies to optimise our half-cell investigations to mimic full device conditions more closely. We have demonstrated that our strategy to engineer iridium catalysts has led to greater than 50% reduction in iridium content necessary in water electrolysers. And yet, our devices show performance and durability comparable to state-of-the-art technology.In this presentation we will discuss remaining challenges for hydrogen production using proton exchange membrane water electrolysers. We will also present materials characterisations and electrochemical performance of our catalysts in half-cell and full device configuration.Reference: K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annu Rev Chem Biomol Eng, 2019, 10, 219-239. M. Bernt, A. Hartig‐Weiß, M. F. Tovini, H. A. El‐Sayed, C. Schramm, J. Schröter, C. Gebauer and H. A. Gasteiger, Chemie Ingenieur Technik, 2020, 92, 31-39. T. Lazaridis, B. M. Stühmeier, H. A. Gasteiger and H. A. El-Sayed, Nature Catalysis, 2022, 5, 363-373. Y. N. Regmi, E. Tzanetopoulos, G. Zeng, X. Peng, D. I. Kushner, T. A. Kistler, L. A. King and N. Danilovic, ACS Catalysis, 2020, 10, 13125-13135.

Towards Low Iridium Loading in Proton-Exchange Membrane Water Electrolysis: Scalable Synthesis of IrOx@TiO2 Core-Shell Particles

Proton-exchange membrane water electrolysis (PEMWE) is a promising technology for producing hydrogen from renewable energy sources. However, the high demand for noble metals hinders the widespread adoption of this technology. Especially the anodic catalyst layer is usually manufactured with high loadings of the scarce element iridium, typically ~2 mgIr·cm-2. As an active and stable noble-metal-free alternative to iridium catalysts has yet to be developed, the most viable strategy for the near future development of PEMWE is to reduce iridium loadings as much as possible. Lowering the iridium loading to values below 0.5 mgIr·cm-2, however, often leads to inhomogeneous catalyst layers resulting in disconnected catalyst islands.1, 2 In two related contributions, we report a novel anodic catalyst for PEMWE that can overcome this limitation by forming homogeneous layers even at lower loadings, thus exhibiting high full cell performance. In this first contribution, we synthesized catalysts with less than 50 wt% iridium content to obtain low iridium loadings while maintaining electrical conductivity. The catalyst is based on the IrO2@TiO2 core-shell microparticles introduced in our previous work,3 which we optimized towards their structural and electrochemical properties. The structural properties of these novel catalysts are analyzed by scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Furthermore, the catalytic activity is evaluated by rotating disk electrode (RDE) measurements, and the electrochemical stability is assessed in a scanning flow cell setup combined with an inductively coupled plasma mass spectrometer (SFC-ICP-MS). Our catalysts outperform state-of-the-art materials in terms of mass activity in RDE measurements, while a comparable dissolution stability is achieved, as evidenced by SFC-ICP-MS measurements. In our second contribution, we show a high performance of this novel catalyst in catalyst-coated membrane (CCM) configuration with iridium loadings below the above mentioned threshold of 0.5 mgIr·cm-2. This proves that our novel IrOx@TiO2 particles with low iridium contents enable a significant reduction of iridium for the anode in PEMWE.

Understanding the Role of Electronic Interactions in Oxide–Supported Iridium Oxide Catalysts for the Oxygen Evolution Reaction

As our society seeks increased energy security and resilience, the need for efficient, cost-effective, carbon-free hydrogen generation will continue to grow. Proton exchange membrane (PEM) water electrolysers are a promising technology to produce “green” hydrogen, however, at present, their large-scale commercialization is hindered by the high capital costs of critical components. The anodic membrane electrode assembly requires large quantities of iridium (Ir) to facilitate the kinetically demanding oxygen evolution reaction (OER). Owing to its scarcity, iridium is a severe bottleneck and expense in the widespread implementation of these technologies. The iridium content in electrolyser anodes can be lowered substantially by designing catalysts which consist of finely dispersed nanoparticles of iridium dioxide affixed onto suitable support materials. This approach enhances the active surface area and operational lifetime of these electrocatalysts towards the OER while utilising a fraction of the otherwise required iridium. To reap these benefits, the support needs to be a high surface area, corrosion-resistant material that is a good electronic conductor1,2. Metal oxides have dominated as oxygen evolution support materials for PEM electrolysis; however, they typically need to be doped with an impurity to demonstrate sufficient electronic conductivity. Iridium oxides supported on antimony−doped tin oxide (ATO) support have been found to behave as high-performing OER electrocatalysts in acidic conditions3,4. While there is no doubt that existing studies prove a link between the presence of ATO support and the improved performance of ATO-supported iridium oxides versus unsupported catalysts, an in-depth characterisation of the charge transfer between the ATO support and deposited IrO2 nanoparticles could prove useful in understanding the reason for these performance enhancements on the basis of the electronic properties of the catalyst and the support.In this study, we investigated the performance of highly dispersed IrO2 nanoparticles, supported on doped tin oxide supports, consisting of various metallic dopants and iridium loadings. The electronic interactions between the Ir-phase and the support were studied by measuring the valence band spectra of the prepared materials with X-ray and ultraviolet photoelectron spectroscopy, and Hall measurements were utilised to understand the nature of electronic conductivity in the prepared materials. The uncovered physicochemical and electronic characteristics are related to the electrochemical performance of these materials towards the OER. These novel findings contribute insights which can be used as the basis for the rational design of next-generation oxide-supported Ir-based catalysts with tunable electronic properties for sustainable PEM electrolysis applications.

Microporous Transport Layers Facilitating Low Iridium Loadings in Polymer Electrolyte Water Electrolyzers

Minimizing iridium content in the anodic catalyst layer (CL) of polymer electrolyte water electrolyzers (PEWE) is essential for facilitating the needed rapid scale-up of hydrogen production capacity. However, reducing the iridium loading inevitably produces thinner CLs (if not changing the catalyst itself). This can have severe effects on performance and stability, mainly due to the losses in the connectivity of the 3D structure. Microporous layers (MPLs) have the potential to improve the performance and catalyst layer utilization of PEWE cells[1], especially at low Ir-loadings since they minimize the in-plane transport length of the required species (i.e. electric and fluidic transport).In this work, we characterized the 3D structure and transport properties of typical IrO2/TiO2 core-shell PEWE catalyst layers[2] by synchrotron-based ptychographic X-ray laminography (PyXL)[3]. Furthermore, we fabricated CLs at different Ir-loadings between 2.5 – 0.1 mgIr cm-2 depositing them either on the membrane i.e. catalyst-coated membranes (CCM) or on the MPL/PTL i.e. porous transport electrode (PTE). We tested the electrodes in PEWE cells using novel MPLs and standard commercial porous transport layers (PTLs) and compared their electrochemical performance and overpotentials. We observe that ultra-low iridium loadings (0.1 mgIr cm-2) with only relatively small setbacks in performance are possible when using Pt-coated MPLs. Moreover, we correlate the electrochemical results with the 3D structure of the CL by PyXL and the MPL/CL interface by lab-based X-ray tomographic microscopy (Figure 1). Finally, we will discuss the challenges of fabricating low-loaded anodic CLs in CCM and PTE configuration and the advantages of using an MPL in both scenarios.[1] T. Schuler, J. M. Ciccone, B. Krentscher, F. Marone, C. Peter, T. J. Schmidt, F. N. Büchi, Adv. Energy Mater. 2020, 10, 1903216.[2] S. De Angelis, T. Schuler, M. Sabharwal, M. Holler, M. Guizar-Sicairos, E. Müller, F. N. Büchi, Sci Rep 2023, 13, 4280.[3] M. Holler, M. Odstrcil, M. Guizar-Sicairos, M. Lebugle, E. Müller, S. Finizio, G. Tinti, C. David, J. Zusman, W. Unglaub, O. Bunk, J. Raabe, A. F. J. Levi, G. Aeppli, Nature Electronics 2019, 2, 464.Figure 1. Surface renderings from XTM/PyXL and SEM images of porous transport electrodes (PTE, left) and catalyst-coated membranes (CCM, right) of selected samples used in this work. Figure 1

Towards Low Iridium Loading in Proton-Exchange Membrane Water Electrolysis: Full-Cell Performance of IrOx@TiO2 Core-Shell Particles in Anode Catalyst Layers

Hydrogen as a promising energy carrier to bridge the gap between supply and demand of renewable energies can be produced by proton-exchange membrane water electrolysis (PEMWE). However, the scarcity of iridium limits the widespread and large-scale implementation of PEMWE. Thus, the state-of-the-art iridium loading for the oxygen evolution reaction (OER) of ~1-2 mgIr·cm-2 must be distinctly reduced.1, 2 A decrease in loading involves a reduction of the catalyst layer (CL) thickness. The reduction is, however, only possible down to a certain threshold (≤ 0.5 mgIr·cm-2), below which the CL shows cracks leading to incomplete connection of the catalyst particles.1, 3 To overcome this issue, we developed a novel catalyst structure with reduced iridium content (< 50 wt% Ir). The synthesized catalyst exhibits a core-shell structure consisting of an insulating TiO2 core (d ≈ 1 µm) coated with iridium oxide (IrOx@TiO2). This optimized structure enables a reduction of the loading while maintaining the thickness and, thus, the electrical connection within the CL.In two related contributions, we demonstrate the suitability of the catalyst by a comprehensive analysis: The first contribution mainly focuses on structural optimization, activity, and stability investigations of the catalyst powder. In this contribution, we optimize the catalyst layer aiming towards high catalyst utilization and in-plane conductivity at iridium loadings below 0.5 mgIr·cm-2. PEMWE full-cell performance is investigated in catalyst-coated membrane (CCM) configuration and the structure and thickness of the CL are characterized by SEM cross-sections. The results of the full-cell tests with our catalyst in comparison to a state-of-the-art IrO2/TiO2 catalyst are shown in Fig. 1. The polarization curve of our catalyst exhibits high OER activity and performance at low loadings (Graph A: 1.76 V @ 1.5 A·cm-2). In comparison to the state-of-the-art catalyst (Graph B), our catalyst outperforms the commercial catalyst in terms of activity. This becomes evident when comparing the HFR-free polarization curves in the low current density region. It could be assigned to a higher catalyst utilization due to the maintained CL thickness or, more likely, to a higher activity of the catalyst itself.1 The performance difference between our and the state-of-the-art catalyst in higher current density regions mainly stems from ohmic losses in the electrode as can be seen from the high frequency resistance (HFR) in Fig. 1. These ohmic losses, however, can supposedly be assigned to the material itself and not to a decreased in-plane conductivity due to a disconnection of parts of the CL.In conclusion, we successfully synthesized an IrOx@TiO2 catalyst with a core-shell structure. This catalyst enables the fabrication of catalyst layers with decreased loadings below 0.5 mgIr·cm-2 while maintaining the catalyst utilization demonstrated in full-cell testing. Therefore, our newly developed catalyst contributes to a scale-up of the PEMWE technology by drastically reducing the demand for the scarce element iridium.Figure 1: Polarization curves, HFR-free polarization curves and HFR values at 80°C (ambient pressure, 100 mlH2O·min-1 on anode) of CCMs fabricated with different anode catalyst types and loading. A: in-house core-shell catalyst with 0.2 mgIr·cm-2 and B: commercial catalyst with 0.3 mgIr·cm-2 (IrO2/TiO2 with 75 wt% Ir, Umicore).References M. Möckl, M. F. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva and H. A. Gasteiger, J. Electrochem. Soc., 169(6), 64505 (2022).C. Minke, M. Suermann, B. Bensmann and R. Hanke-Rauschenbach, Int. J. of Hydrog. Energy, 46(46), 23581–23590 (2021).M. Bernt, A. Siebel and H. A. Gasteiger, J. Electrochem. Soc., 165(5), F305-F314 (2018). Figure 1

Iridium Catalyst Immobilized on Crosslinked Polyethyleneimine for Continuous Hydrogen Production Using Formic Acid.

Hydrogen is an alternative fuel that can play a critical role in achieving net zero emissions, leading to global environment sustainability. An iridium-immobilized catalyst based on polyethyleneimine (PEI) was synthesized and utilized for hydrogen production via formic acid dehydrogenation (FADH). Iridium complex is cross-linked with its ligand and PEI to form the immobilized catalyst, where the iridium content could be easily varied in the range of 1-10 %. The structure of the iridium-immobilized catalyst was confirmed using solid-state NMR, DNP NMR, and FTIR spectroscopies. The iridium-immobilized catalyst with PEI showed excellent catalytic activity for FADH, exhibiting the catalyst's highest turnover frequency (TOF) value of 73 200 h-1 and a large turnover number (TON) value of over 1 130 000. The catalyst could be used for continuous hydrogen production via FADH, exhibiting high durability for over 2 000 h with TON value of 332 889 without any degradation in catalytic activity. The obtained hydrogen gas was evaluated for power generation using a standard fuel cell, as well as achieved 5 h of stable power generation.

Selection on antimony-doped tin oxide (ATO) as an efficient support for iridium-based oxygen evolution reaction (OER) catalyst in acidic media

Reducing the iridium content while preserving high OER activity is an important prerequisite for the progress of inexpensive anodic water splitting electrocatalysts in low pH medium. Here we report the effects of bulk and surface structures of antimony doped tin oxide (ATO) supports on the ATO supported Ir-based electrocatalyst's activity for oxygen evolution reaction (OER) in acidic media. Ability of the ATO supports to anchor the Ir nanoparticles, measured as the fraction of Ir species from reaction bath landed on ATO support (conversion efficiency; ηc), is found to be strongly dependent on its surface chemistry, characterized in terms of presence of surface oxygen groups (Osurface). Both Osurface content and electronic conductivity of ATOs show strong influence on OER activity. In general, high conductivity and low Osurface content are preferred for high OER activity, though low Osurface may compromise ηc. The optimal catalyst demonstrates superior OER activity of 777 A g−1, 2.5 times that of the state-of-the-art commercial catalyst at 1.65 V vs. RHE. Further, the synthesized catalysts exhibit durability comparable to that of the commercial counterpart.

IrO2 Nanoparticle-Decorated Ir-Doped W18O49 Nanowires with High Mass Specific OER Activity for Proton Exchange Membrane Electrolysis.

The oxygen evolution reaction (OER) severely limits the efficiency of proton exchange membrane (PEM) electrolyzers due to slow reaction kinetics. IrO2 is currently a commonly used anode catalyst, but its large-scale application is limited due to its high price and scarce reserves. Herein, we reported a practical strategy to construct an acid OER catalyst where Iridium oxide loading and iridium element bulk doping are realized on the surface and inside of W18O49 nanowires by immersion adsorption, respectively. Specifically, W0.7Ir0.3Oy has an overpotential of 278 mV at 10 mA·cm-2 in 0.1 M HClO4. The mass activity of 714.10 A·gIr-1 at 1.53 V vs. the reversible hydrogen electrode (RHE) is 80 times that of IrO2, and it can run stably for 55 h. In the PEM water electrolyzer device, its mass activity reaches 3563.63 A·gIr-1 at the cell voltage of 2.0 V. This improved catalytic performance is attributed to the following aspects: (1) The electron transport between iridium and tungsten effectively improves the electronic structure of the catalyst; (2) the introduction of iridium into W18O49 by means of elemental bulk doping and nanoparticles supporting for the enhanced conductivity and electrochemically active surface area of the catalyst, resulting in extensive exposure of active sites and increased intrinsic activity; and (3) during the OER process, partial iridium elements in the bulk phase are precipitated, and iridium oxide is formed on the surface to maintain stable activity. This work provides a new idea for designing oxygen evolution catalysts with low iridium content for practical application in PEM electrolyzers.

The effect of copper and iridium input atoms on the recombination properties of silicon

In monocrystalline silicon, which is easily condensed with copper and iridium, the recombination time is more stable compared to conventional samples. If the concentration of recombination centers in silicon is less than the concentration of adhesion levels, the residence time of non-basic charge carriers increases, and its values are determined by the concentration of adhesion levels. Compared to conventional silicon samples that were legalized with copper and iridium, a large concentration of copper and iridium was observed in neutron-legalized samples. Сoncentration maxima are observed in the DLTS spectra after thermal diffusion of samples of n-Si&lt;P,R,Cu&gt;, n-Si&lt;P,P,Ir&gt; at 1150 oC. This was followed by the study of the structure, size and distribution of silicon mixing defects, which was legitimized by copper and iridium, using ATM.

Abu Hureyra, Syria, Part 3: Comet airbursts triggered major climate change 12,800 years ago that initiated the transition to agriculture

This study investigates the hypothesis that Earth collided with fragments of a disintegrating comet, triggering Younger Dryas climate change 12,800 years ago. This collision created environmental conditions at Abu Hureyra, Syria, that favored the earliest known continuous cultivation of domestic-type grains and legumes, along with animal management, adding to the pre-existing practice of hunting-and-gathering. The proposed airburst coincided with a significant decline in local populations and led to architectural reorganizations of the village. These events immediately followed the deposition of the Younger Dryas Boundary layer that contains peak concentrations of high-temperature meltglass, nanodiamonds, platinum, and iridium. These proxies provide evidence of a nearby low-altitude airburst by a comet-like fragment of a former Centaur, one of many &lt;300-km-wide bodies in unstable orbits between the giant planets. This large body is proposed to have undergone cascading disintegrations, thus producing the Taurid Complex containing Comet Encke and ~90 asteroids with diameters of ~1.5 to 5 km. Here, we present substantial new quantitative evidence and interpretations supporting the hypothesis that comet fragments triggered near-global shifts in climate ~12,800 years ago, and one airburst destroyed the Abu Hureyra village. This evidence implies a causative link between extraterrestrial airbursts, environmental change, and transformative shifts in human societies.

The effect of iridium content in boron carbide-supported iridium catalyst on the activity and stability of proton exchange membrane water electrolyzer

One of the major obstacles to proton exchange membrane water electrolyzer (PEMWE) for large-scale applications is the cost of iridium for oxygen evolution reaction (OER). To resolve this issue, boron carbide-supported iridium catalysts are prepared by varying the iridium content from 10 to 60 wt%. Increasing the iridium content on the boron carbide support affects the physical properties of the catalysts and the electronic structure of iridium. At the content of 40%, Ir/B4C showed the highest catalytic activity mainly due to its high electrochemical surface area. 40%-Ir/B4C showed outstanding cell performance of 1.0 A/cm2 at 1.61 V with a loading of 0.5 mg⋅Ir/cm2 which has the same performance with 3.0 mg⋅Ir/cm2 of unsupported commercial catalyst. 40%-Ir/B4C also showed excellent durability in a half-cell as well as in a single cell. The presence of Ir (IV) and the metal-support interaction help 40%-Ir/B4C to be stable.