Platinum Group Research Articles

Platinum-Group Element and Trace Element Contents of Chromite Grains from the Alexo Komatiite Flows Compared with Chromites from Other Volcanic Rocks: Implications for the Use of Chromite Compositions in Petrogenesis

Platinum-Group Element and Trace Element Contents of Chromite Grains from the Alexo Komatiite Flows Compared with Chromites from Other Volcanic Rocks: Implications for the Use of Chromite Compositions in Petrogenesis

MIL-101(Cr) entrapped polyol-synthesized iron promoted platinum bimetallic nanoparticles system for synergistic selective hydrogenation of cinnamaldehyde

The interfacial characteristics of platinum (Pt) metal catalysts can be systematically regulated by interacting them with electropositive metals, leading to synergistic interactions for extensive catalytic applications. In this study, an evenly dispersed polyol-synthesized iron (Fe)-promoted Pt bimetallic nanoparticle (BNPs) system was embedded in MIL-101(Cr). The PtFe2@MIL-101(Cr) catalyst unveiled remarkable activity (86%) and selectivity (89%) for the superior hydrogenation of the targeted CO bond of cinnamaldehyde (CAL). The exceptional hydrogenation performance can be credited to the interplay of the geometric and electronic properties arising from charge shuttling between Fe and Pt within the homogenously distributed Pt–Fe bimetallic nanoparticle system. The experimental results indicate enhanced valence electrons in the Pt d-band through the mutual synergetic interface between the Pt and Fe BNPs. Consequently, these Fe–Pt sites functioned as interfacial electrophilic and nucleophilic (Lewis acid-base) sites, enhancing H2 activation and facilitating CO bond conversion to yield unsaturated cinnamal alcohols (COL). Additionally, the narrow pores of MIL-101(Cr) encapsulating the Pt–Fe BNPs induced steric hindrance, allowing only CO bond hydrogenation. Furthermore, the PtFe2@MIL-101(Cr) catalyst maintained its optimal hydrogenation performance over five cycles, demonstrating no substantial loss in either CAL conversion or COL yield, thus endorsing the universal practical applicability of the catalyst.

SIMS U-Pb dating of baddeleyite-zircon pairs in mafic rocks to determine the ages of magmatic mineralization and hydrothermal remobilization in a Ni-Cu-(PGE) deposit

Ni-Cu-(PGE) sulfide deposits associated with mafic–ultramafic rocks are the most important sources of Ni and platinum-group elements (PGE) in the world. These deposits also contain significant amounts of Cu. Such deposits are generally considered to have formed by multiple stages of primary magmatic concentration and secondary hydrothermal remobilization. However, constraining the ages of Ni-Cu-(PGE) sulfide deposits has proven challenging, particularly those that have experienced post-magmatic hydrothermal overprinting and remobilization. The lack of robust geochronology data has hindered understanding of the geological controls on this important type of mineralization. The Chibaisong Ni-Cu-(PGE) sulfide deposit in the North China Craton is characterized by disseminated and net-textured ores formed by magmatic processes and overprinted by hydrothermal Cu-rich vein stockwork. The Cu-rich vein stockwork is fracture-controlled, and contains a mineral assemblage of Ni-Cu sulfides (chalcopyrite, pyrrhotite, pentlandite), amphibole and quartz. Chalcopyrite in the hydrothermal stockwork is relatively depleted in Ni but enriched in Ag and Cd compared with disseminated magmatic chalcopyrite, typical of hydrothermal superimposed ores as documented elsewhere. We identified baddeleyite-zircon pairs associated with Ni-Cu sulfides in hydrothermal superimposed ores of the Chibaisong deposit, in which the baddeleyite is unequivocally of primary igneous origin whereas the zircon represents the replacement product of baddeleyite during hydrothermal alteration. In situ SIMS U-Pb dating of baddeleyite and zircon yielded weighted mean 207Pb/206Pb ages of 2181 ± 21 Ma and 1892 ± 33 Ma, respectively, interpreted as the timing of magmatic mineralization and subsequent hydrothermal remobilization of the Ni-Cu-(PGE) deposit. Our results explain the large discrepancies in sulfide Re-Os ages previously obtained from this deposit. This study demonstrates that on the basis of detailed BSE imaging, in situ SIMS U-Pb dating of baddeleyite-zircon pairs can provide robust age constraints for both magmatic mineralization and hydrothermal remobilization of Ni-Cu-(PGE) sulfide deposits hosted in mafic–ultramafic intrusions, although further studies are needed to test whether the formation of such deposits commonly entails multiple stages of hydrothermal remobilization. Since baddeleyite or baddeleyite-zircon pairs are common accessory minerals in Ni-Cu-(PGE)-bearing mafic–ultramafic rocks, the dating approach employed in this study may be applicable to similar deposits elsewhere.

Nature of the Active Center for the Oxygen Reduction on Ag-Based Single-Atom Alloy Clusters.

The development of alternative alloy catalysts with high activity, surpassing platinum group metals, for the oxygen reduction reaction (ORR) is urgently needed in the field of electrocatalysis. The Ag-based single-atom alloy (AgSAA) cluster has been proposed as a promising catalyst for the ORR; however, enhancing its activity under operational conditions remains challenging due to limited insights into its actual active site. Here, we demonstrate that the operando formation of the MO x (OH) y complex serves as the key active site for catalyzing the ORR over AgSAA cluster catalysts, as revealed through comprehensive neural network potential molecular dynamics simulations combined with first-principles calculations. The volcano plot of the ORR over the MO x (OH) y complex addresses the gaps inherent in traditional metallic alloy models for pure AgSAA cluster catalysts in ORR catalysis. The appropriate orbital hybridization between OH and the dopant metal in the MO x (OH) y complexes indicated that the Ag54Co1, Ag54Pd1, and Ag54Au1 clusters are optimal AgSAA catalysts for the ORR. Our work underscores the significance of theoretical modeling considering the reaction atmosphere in uncovering the true active site for the ORR, which can be extended to other reaction systems for rational catalyst design.

An Overview of Noble Metal Nanoparticles and Their Application in the Treatment of Cancer Diseases

Noble metals and their compounds have been used as therapeutic agents since ancient times in medicine to treat various infections. Recently, many advances have been made in the field of nanotechnology to develop different types of nanomaterials with a wide range of applications. Among metal nanoparticles, noble metal nanoparticles have shown potential biomedical applications. Due to their small size, nanoparticles can easily communicate with biomolecules both on the surface and inside cells and bring better targeting for diagnosis and treatment. Noble metal nanoparticles inspire researchers due to their significant role in the diagnosis and treatment of unpleasant diseases. In this review article, we focus on the biomedical applications of noble metal nanoparticles, especially silver, gold, and platinum, in cancer diagnosis and treatment.

Platinum Group Metals against Parasites: State of the Art and Future Perspectives

Background: Globally, parasitic diseases are considered among the neglected diseases. Clinically, several drugs are used in treatment, however due to drug resistance and multidrug resistance and the low investment in new research lines, there has been a failure in the treatment of parasitic illnesses. Objectives: The present mini-review is a comprehensive review of the use of platinum group metals as biological agents. It aims to establish the actual state of the art of these metal elements in the antiparasitic activity-specific area and define the future possibilities of action. Methods: The review comprises more than 100 research works done in this field. The differences between platinum group metals chemistry and their use as metal complexes with biological activity have been discussed. Results: This review highlighted the platinum group metal's potential as an antiparasitic agent for different diseases. Conclusion: The review will be helpful for the researchers involved in targeted drugs for parasitic disease therapy.

Toxicological Implications of Platinum Group Elements (PGEs): A Systematic Review of In Vivo and In Vitro Studies Using Mammalian Models.

The six Platinum group metal elements (PGEs) comprising Ruthenium, Rhodium, Palladium, Platinum, Iridium and Osmium are grouped together in the periodic table. Human activities are mostly responsible for releasing PGEs into the environment. This systematic review focused on three PGEs with the greatest anthropogenic use, including in vehicle catalytic converters: Platinum (Pt), Palladium (Pd), and Rhodium (Rh). Consequently, these represent the greatest contributors to environmental pollution. The current review of in vivo toxicological studies (mammalian models) and in vitro cell exposure studies examined the potential harmful effects of these metalloids to mammalians, and their possible toxicity to human health. We applied Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology to conduct a comprehensive search and evaluation of records in the available literature published between 01/01/2009 and 01/15/2024 in four databases. PROSPERO code ID: CRD42024471558. Results concerning the health effects of PGEs were extracted from articles according to the inclusion and exclusion criteria. After screening the records for eligibility, 22 studies were included in the final analysis. This systematic review revealed that airborne PGEs significantly increased the activation of pathologic pathways in several human organs and/or perturbed various metabolic pathways. In view of the known pro-inflammatory and organ-degenerative effects of PGEs, the paucity of studies on the effect of PGEs on the central nervous system and on possible correlations with neurodegenerative diseases were particularly evident. The clinical complexity and chronic nature of PGE-related pathologies indicate that targeted research is essential. In light of the increasing incidence of non-communicable diseases, particular attention should be paid to the design of epidemiological studies and to environmental monitoring services.

Waste for Product-Synthesis and Electrocatalytic Properties of Palladium Nanopyramid Layer Enriched with PtNPs.

The presented research is the seed of a vision for the development of a waste-for-product strategy. Following this concept, various synthetic solutions containing low concentrations of platinum group metals were used to model their recovery and to produce catalysts. This is also the first report that shows the method for synthesis of a pyramid-like structure deposited on activated carbon composed of Pd and Pt. This unique structure was obtained from a mixture of highly diluted aqueous solutions containing both metals and chloride ions. The presence of functional groups on the carbon surface and experimental conditions allowed for: the adsorption of metal complexes, their reduction to metal atoms and enabled further hierarchical growth of the metal layer on the carbon surface. During experiments, spherical palladium and platinum nanoparticles were obtained. The addition of chloride ions to the solution promoted the hierarchical growth and formation of palladium nanopyramids, which were enriched with platinum nanoparticles. The obtained materials were characterized using UV-Vis, Raman, IR spectroscopy, TGA, SEM/EDS, and XRD techniques. Moreover, Pd@ROY, Pt@ROY, and Pd-Pt@ROY were tested as possible electrocatalysts for hydrogen evolution reactions.

Platinum-Group Elements and Nb-Ta geochemistry of the Deccan basalts from Kumbharli and other Ghat sections and the Koyna Seismic Zone, Maharashtra (India): Crustal contamination and implication for sulfide saturation of the magma

The Deccan basalts from Kumbharli, Nadlapur, Bijaynagar, Hazarmacchi, and Surli Ghat sections (surface samples) and the Koyna borehole-7 (KBH-7, sub-surface samples) from Maharashtra (western India) demonstrate a two-stage crystallization process. Olivine and chromite were crystallized earlier in a shallow crustal magma chamber while clinopyroxene and plagioclase phenocrysts were crystallized in the sub-volcanic conduits forming the crystal mush, and carried to the surface by the evolved Fe-Ti-rich ascending basaltic magma. The high modal abundance of plagioclase at the top and clinopyroxene at the bottom part of the Kumbharli Ghat section is responsible for an increase in Sr and a decrease in Sc content towards the upper flows. The surface and sub-surface basalt samples contain Pd = 5–31 ppb, Pt = 4–15 ppb, Ir = 1–4 ppb, Ru = 1–3 ppb, and Rh = 3–5 ppb. Negative relations of Pd/Ir, Pd/Ru, and Pd/Rh with MgO from both sets of samples indicate partitioning of Ir, Ru, and Rh to early fractionated cumulus chromite (or olivine). Magnetite is a late crystallizing phase from the evolved Fe-Ti-rich basaltic magma. With an increasing modal abundance of magnetite, there is an increase of FeO total , TiO 2 , and V with Pd indicating fractionation of Pd by magnetite. Geochemical characters show that the surface basalt samples are less contaminated compared to the sub-surface KBH-7 basalts. High Nb (6.8–13.6 ppm) and low Ta (0.2–0.37 ppm) content and elevated Nb/Ta ratios of the surface samples from the ghat sections indicate the possible interaction of the basaltic magma with the carbonate metasomatized subcontinental lithospheric mantle (SCLM). On the other hand, a high degree of partial melting with limited crustal contamination can also elevate the Nb/Ta ratios of the basalts from the ghat sections. Deccan basalts from the study areas do not bear the signature of sulfide supersaturation and subsequent immiscible sulfide segregation. This is evidenced by their high chalcophile element concentrations (Ni = 79–103 ppm, Cu = 121–259 ppm) and ratios like Cu/Zr (≥ 1), Ni/MgO (13.7–21.8) with low Cu/Pd (2140–29938) compared to other Ni-Cu (PGE) sulfide mineralized continental flood basalts. The lack of crustal sulfur in the various contaminants is perhaps the main reason for this sulfide-undersaturated character of the Deccan basalts of the current study.

Deccan volcanism's influence on Chicxulub impact signatures at the continental Cretaceous-Paleogene boundary in the Sichuan Basin, China

The Cretaceous-Paleogene (K-Pg) extinction is linked to two primary causes: the Chicxulub asteroid impact in Mexico and the Deccan Traps eruptions in India. While substantial geological evidence supporting both events has been found worldwide, to understand their potential interactions, it is crucial to study sites that preserve records of both events simultaneously. The terrestrial K-Pg boundary located in the Sichuan Basin, China (∼15,500 km from the Chicxulub Crater and ∼5,600 km from the Deccan Traps correspond to 66 Ma), preserves evidence of both the Chicxulub impact and the Deccan Traps eruptions, along with the effects of subsequent events on the earlier ones. It offers a new perspective on the K-Pg boundary. Detailed petrological examination and geochemical analyses, including platinum-group element (PGE) and black carbon concentrations, were conducted across a 2 m K-Pg boundary section. The K-Pg boundary layer (∼2.5 cm thick) is composed of very fine-grained, brick-red sandstone and exhibits significant enrichments in Ir (9.050 ppb) and Os (10.72 ppb), along with elevated black carbon (1.10 ‰), strongly indicating contributions from the impact. Intriguingly, another PGE anomaly was detected approximately 50 cm below the K-Pg boundary. The strata surrounding the K-Pg boundary display evidence of alteration by acidic and HSˉ-rich fluids. These fluids likely caused the observed downward migration of PGE within the boundary, resulting in two distinct PGE anomalies - one at the K-Pg boundary itself and another approximately 50 cm below. These fluids resulted in the overlying sandstones exhibiting minimal matrix content and bleached the underlying brick-red sandstones. Volcanic gas emissions from the Deccan Traps after the impact are a potential source for these fluids. Our findings support the hypothesis that the most voluminous Deccan eruptions had occurred close to, but not necessarily immediately after, the Chicxulub impact, potentially lasting 100–131 ka. The hiatus after the impact weakens the possibility of a direct causal link between the Deccan eruptions and the impact.

Efficient Recovery of Platinum Group Metals from Spent Automotive Catalysts Using Iron Smelting Method by Optimizing Slag Composition at Low Temperature

Efficient Recovery of Platinum Group Metals from Spent Automotive Catalysts Using Iron Smelting Method by Optimizing Slag Composition at Low Temperature

Ruthenium isotopes show the Chicxulub impactor was a carbonaceous-type asteroid.

An impact at Chicxulub, Mexico, occurred 66 million years ago, producing a global stratigraphic layer that marks the boundary between the Cretaceous and Paleogene eras. That layer contains elevated concentrations of platinum-group elements, including ruthenium. We measured ruthenium isotopes in samples taken from three Cretaceous-Paleogene boundary sites, five other impacts that occurred between 36 million to 470 million years ago, and ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers. Our data indicate that the Chicxulub impactor was a carbonaceous-type asteroid, which had formed beyond the orbit of Jupiter. The five other impact structures have isotopic signatures that are more consistent with siliceous-type asteroids, which formed closer to the Sun. The ancient spherule layer samples are consistent with impacts of carbonaceous-type asteroids during Earth's final stages of accretion.

Influence of Domain Size and Support Composition on the Reducibility of SiO2 and TiO2 Supported Tungsten Oxide Clusters.

Supported tungsten oxides are widely used in a variety of catalytic reactions. Depending on the support, the cluster size, oxidation state, reducibility and speciation of the tungsten oxides can widely differ. When promoted with a platinum group metal, the resulting spillover of hydrogen may facilitate the reduction of supported tungsten oxide species, depending on the support. High resolution scanning transmission electron microscopy imaging showed nanometer scale WO x clusters were synthesized on SiO2 whereas highly dispersed species were formed on TiO2. Results from H2-temperature-programmed reduction showed the presence of Pd lowered the initial reduction temperature of SiO2-supported WO x species but interestingly did not affect that of TiO2-supported WO x . X-ray photoelectron and absorption spectroscopies showed the W atoms in SiO2-supported WO x species reduce from a +6 oxidation state to primarily +5 after thermal treatment in 5% H2, while the fraction of W in the +5 oxidation state was relatively unaffected by reduction treatment of TiO2-supported WO x . The unusual behavior of TiO2-supported WO x was explained by quantum chemical calculations that reveal the lack of change in the oxidation state of W is attributed to charge delocalization on the surface atoms of the titania support, which does not occur on silica. Moreover, modeling results at <600 K in the presence of H2 suggest the formation of Brønsted acid sites, and the absence of Lewis acid sites, on larger aggregates of WO x on silica and all cluster sizes on titania. These results provide experimental and theoretical insights into the nature of supported tungsten oxide clusters under conditions relevant to various catalytic reactions.

Aloe vera gel mediated green synthesis of ruthenium nanoparticles and their potential anticancer activity

Metal nanoparticles have a noteworthy future in cancer treatment research because of their smaller size and large active surface area. Though gold, silver, platinum, palladium, copper, zinc, iron and several other metal nanoparticles have been explored for their anticancer potential in different pathways, the main limitation of these particles is their toxicity which may be controlled through their size, surface modification and route of administration. Compared to other metal nanoparticles, ruthenium nanoparticles have high bio compatibility and they exhibit excellent photo-thermal effect. Though there are several reports in the literature on the anticancer potential of ruthenium complexes, ruthenium nanoparticles are not much investigated. In the present work, therefore, an attempt has been made to synthesize ruthenium nanoparticles in an easy and eco-friendly way using Aloe vera gel. Ruthenium chloride was used as a precursor and Aloe vera gel acted both as reducing and capping agent. The synthesized ruthenium nanoparticles were characterized using UV-Visible spectrophotometry, Fourier Transform Infrared Spectroscopy (FT-IR), High Resolution Transmission Electron Microscopy (HRTEM), Powder X-ray Diffraction (PXRD), Dynamic Light Scattering (DLS) and Field Emission Scanning Electron Microscopy (FESEM). The analyses confirmed the formation of nano globules of Aloe vera gel of diameter in the range 90–300 nm with ruthenium nanoparticles of average size 1.5 nm embedded in them. The synthesized Ru nanoparticles embedded in the nano globules of Aloe vera gel (ALV RuNPs) were explored for their anticancer potential in the Dalton's lymphoma ascites (DL) cell line using Trypan Blue assay. The results of the assay showed that the ALV RuNPs can induce concentration dependent cytotoxicity in DL cancer cells. Approximately 40 % cytotoxicity was obtained for concentration range 5–50 mg/mL of the sample while negligible cytotoxicity was observed for healthy PBMC cells. Theoretical study indicates significant interaction between the components present in Aloe vera and Ru-nanoparticles. The results showed that ruthenium nanoparticles can emerge as a promising bio-compatible candidate with the ability to selectively target cancer cells while sparing normal cells.

Ultrasonic Interactions with Microstructural Defects in Platinum Group Metal Nitrides OsN, IrN and PtN

Ultrasonic Interactions with Microstructural Defects in Platinum Group Metal Nitrides OsN, IrN and PtN

Accelerated Discovery of Multi-Metallic Nanostructured Catalysts for Anion Exchange Membrane Water Electrolyzers: Oxygen Evolution Reaction

The current reliance on platinum group metals (PGMs) as electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) water electrolyzers, the current industry standard, presents a significant barrier to the widespread adoption of hydrogen as a clean energy carrier. The scarcity and high cost of PGMs necessitate the development of alternative materials and technologies that offer comparable performance at a reduced cost. In this context, anion exchange membrane (AEM) water electrolyzers have emerged as a promising alternative.This presentation addresses this imperative by focusing on the design and synthesis of nanostructured mesoporous multi-metallic catalysts for AEM water electrolyzers, leveraging earth-abundant materials as alternatives to the rare and expensive PGMs currently employed in PEM water electrolyzers. Transition metal oxides, sulfides, and phosphides are promising candidates to replace PGMs, given their abundance, low cost, and tunable catalytic properties conducive to high OER activity. The OER activity and durability of newly developed multi-metallic transition metal catalysts in an alkaline environment will be discussed in this presentation.Preliminary results demonstrate that the developed catalysts exhibit high OER activity, achieving a potential of <1.5 V versus RHE at a current density of 10 mA cm⁻² in 1.0 M KOH. Notably, this surpasses the performance of commercial OER catalysts in alkaline environments. Furthermore, the catalyst exhibits superior durability, with < 0.5 mV/h potential loss over 100 h durability test at 10 mA cm⁻² in 1.0 M KOH.AcknowledgmentsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). Argonne is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under Contract DE-AC-02-06CH11357 .

Low-Temperature Wastewater Electrolysis for H2 and Clean Water Generation

Water electrolysis represents a sustainable approach to produce green hydrogen (H2); however, the high energy cost (H2O → 2H+ + 2e- + ½O2, ∆H° = 275 kJ/mol H2, E° = −1.18 V) associated with water electrolysis and electricity cost (>$50/MWh) results in a minimum H2 selling price ≈$4/kg H2. Hence, we need to find alternative process to generate H2 to meet the current U.S. Department of Energy's (DOE's) Energy Earthshots of $1/kg H2 in one decade.Wastewater electrolysis represents an alternative approach to generate H2 with renewable sources by electrochemically oxidizing organic molecules to generate H2 (e.g., CH3COOH + 2H2O → 2CO2 + 8e- + 8H+, ∆H° = 53 kJ/mol, E° = −0.02 V,) which has up to 5 times lower energy requirement than water electrolysis. As opposed to water electrolysis that requires clean water streams, wastewater electrolysis uses readily available waste streams that need cleanup anyway to generate H2; hence, integrating a second application in addition to H2 generation.1-3 In this work, we compare the performance of heterogeneous electrocatalysts for the electrocatalytic oxidation (ECO) of organic molecules present in wastewater as well as electrocatalysts for the H2 evolution reaction (HER) at room temperature. ECO electrocatalysts were developed and tested using real wastewaters derived from several sources including the hydrothermal liquefaction (HTL) of food waste. We synthesized the ECO electrocatalysts using both platinum-group metals (PGM) as well as base-group metals (BGM) with equimolar loadings and tested them as a function of half-cell potential. Our results show that both PGM- and BGM-based bimetallics improve the activity and stability compared to the baseline RuO2-based catalysts4-6. We performed a preliminary techno-economic analysis and showed that the levelized costs of using this technology to process the wastewater alone is equivalent to that of traditional wastewater processing. The sale of the produced H2 co-product will decrease the levelized processing cost below that of current wastewater processing. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J. D.; Koh, K.; Sanyal, U.; Song, M.; Li, D.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chemistry & Engineering 2020, 8 (11), 4407-4418.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. Journal of Applied Electrochemistry 2021, 51 (1), 107-118.Lopez-Ruiz, J. A.; Andrews, E.; Akhade, S. A.; Lee, M.-S.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V.-A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the Role of Metal and Molecular Structure on the Electrocatalytic Hydrogenation of Oxygenated Organic Compounds. ACS Catalysis 2019, 9 (11), 9964-9972.Qiu, Y.; Lopez-Ruiz, J. A.; Zhu, G.; Engelhard, M. H.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles. Appl. Catal. B-Environ. 2022, 305, 121060.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118.Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277. Figure 1

Electrochemistry of 2D Nanosheets Based on Platinum Group Metals

Electrocatalysts and electrode materials based on platinum group metal (PGMs) and thier oxides are one of the most well studied materials for energy storage and conversion applications.1,2 As such materials are scarce, downsizing is critical for practical applications and various nanomaterials have been synthsized so far. 2D nanostructures (nanosheets) are particularly promising, owing not only to the high surface/volume ratio, but also to the stability originating from the 2D extended bonds. This talk will attempt to provide a summary of state-of-the-art PGM nanosheets and a critical assessment on the possible applications of such innovative nanomaterials. We will present and discuss recent advancement on the synthesis and structure-property relation of PGM oxide nanosheets based on RuO2 and IrO2 for supercapacitor3-5 application as well as electrocatalysts.6,7 In addition, electrocatalytic activity of Pt and core-shell Pt nanosheets will be presented.8-11 1. W. Sugimoto, Electrochemistry, 86, 281–290 (2018) DOI: 10.5796/electrochemistry.18-6-E2668.2. W. Sugimoto and D. Takimoto, Chem. Lett., 50, 1304–1312 (2021) DOI: 10.1246/cl.210087.3. W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, and Y. Takasu, Angew. Chem. Int. Ed., 42, 4092–4096 (2003) DOI: 10.1002/anie.200351691.4. K. Fukuda, T. Saida, J. Sato, M. Yonezawa, Y. Takasu, and W. Sugimoto, Inorg. Chem., 49, 4391–4393 (2010) DOI: 10.1021/ic100176d.5. K. Sonobe, S. Tominaka, and W. Sugimoto, J. Am. Chem. Soc., 144, 15008–15012 (2022) DOI: 10.1021/jacs.2c05951.6. D. Takimoto, K. Fukuda, S. Miyasaka, T. Ishida, Y. Ayato, D. Mochizuki, W. Shimizu, and W. Sugimoto, Electrocatalysis, 8, 144–150 (2017) DOI: 10.1007/s12678-016-0348-4.7. D. Takimoto, Y. Ayato, D. Mochizuki, and W. Sugimoto, Electrochemistry, 85, 779–783 (2017) DOI: 10.5796/electrochemistry.85.779.8. K. Fukuda, J. Sato, T. Saida, W. Sugimoto, Y. Ebina, T. Shibata, M. Osada, and T. Sasaki, Inorg. Chem., 52, 2280–2282 (2013) DOI: 10.1021/ic302720d.9. D. Takimoto, T. Ohnishi, J. Nutariya, Z. Shen, Y. Ayato, D. Mochizuki, A. Demortière, A. Boulineau, and W. Sugimoto, J. Catal., 345, 207–215 (2017) DOI: 10.1016/j.jcat.2016.11.026.10. J. Nutariya, E. Kuroiwa, D. Takimoto, Z. Shen, D. Mochizuki, and W. Sugimoto, Electrochim. Acta, 283, 826–833 (2018) DOI: 10.1016/j.electacta.2018.07.005.11. D. Takimoto, S. Toma, Y. Suda, T. Shirokura, Y. Tokura, K. Fukuda, M. Matsumoto, H. Imai, and W. Sugimoto, Nat. Commun., 14, 19 (2023) DOI: 10.1038/s41467-022-35616-4.

Towards High-Performance AEM Water Electrolyzers: Transitioning from PGM to Low-PGM and PGM-Free Electrocatalysts

Hydrogen, known for its high gravimetric energy density and low environmental impact, is widely regarded as a promising low-carbon energy carrier. The production of hydrogen via water electrolysis offers a valuable opportunity to efficiently utilize renewable energy resources – both as a storage and transport medium and to produce hydrogen that is a crucial feedstock for multiple industrial and manufacturing applications. Among various water electrolysis technologies, anion exchange membrane water electrolyzers (AEMWEs) are notable for their distinct and advantageous features. Their alkaline operational environment significantly reduces corrosion, allow for the possibility to use catalysts and cell component materials that are earth abundant and cost effective. Moreover, the use of anion exchange membranes (AEMs) as the electrolyte and zero-gap design enhance operational efficiency and hydrogen production rates compared to traditional alkaline electrolyzers. These benefits position AEMWEs as a compelling solution for efficient, cost-effective large-scale hydrogen production.To date, the development of lower-cost AEMWEs has been hindered by several challenges. A critical issue is the activity and durability of catalysts, particularly those that are platinum group metal (PGM)-free. This leads many researchers and electrolyzer manufacturers to lean on PGM catalysts at both the anode and cathode. These catalysts, while effective, significantly increase the cost and complexity of the system, posing a barrier to widespread adoption and commercialization of AEMEL technology in the burgeoning hydrogen economy. PGM-free anodes have been demonstrated for the AEMWE, but there have been fewer PGM-free options for the cathode.This study assessed the performance and durability of various low-PGM and PGM-free electrocatalysts for the oxygen evolution (OER) and hydrogen evolution (HER) reactions. We focused on Lanthanum Strontium Cobalt (LSC), Nickel Ferrite (NiFeOx), and Lead Ruthenate (PbRuOx) for the OER at the anode, and Nickel Molybdenum (NiMo), Nickel Rhenium (NiRe), and a low-PGM PtNi for the HER at the cathode. Furthermore, the performance of the NiMo HER catalyst was enhanced by optimizing the physical properties of both the catalyst powder and the electrodes. These experimental results offer crucial insights into developing PGM-free AEM water electrolyzer systems, marking a progressive step towards their commercial feasibility.

Hydrogen Evolution Reaction: Log j0 Versus Work Function Φ As Viewed from Transition State Theory As an Eyring Plot

In 1972, Trasatti correlated the log of the exchange current density (j0) for the hydrogen evolution reaction (HER) with the work functions of 31 metal electrodes to yield two parallel regression lines. [1] The lines are separated by Δ log j0 = 3. Thermodynamically, work function 𝚽 is the energy to remove an electron from a metal to infinity. Perhaps counterintuitively, platinum group metals (PGMs) with the highest 𝚽 sustain the highest j0 values.The elementary, interfacial electron transfer occurs between the electrode and adsorbed hydrogen cation and adsorbed hydrogen atom.H+ ads + e ⇌ H● ads A materials dependent rate expression is developed as follows. [2]The properties of the metal are introduced explicitly into reaction mechanism, characterized by M(e) and M(0), the metal electrode with and without the electron.M(e) + H+ ads ⇄ M(0) + H● ads Classical transition state theory (TST) characterizes the free energy of activation ΔG‡ as the energy difference between the transition state (TS) and the minimum energy of the reactants. The TS forms at equilibrium, where adsorbed hydrogen and metal electrode share the electron.M(e) + H+ ads ⇌ [M ●●● e ●●● Hads]‡ ⇌ M(0) + H● ads Electrochemical potentials set the energy difference in the products and reactant, which sets ΔG‡. Chemical potential (𝞵) difference for the metal without and with the electron define 𝚽. F𝚽 = 𝞵M(0) - 𝞵M(e) F𝚽 is further defined as a chemical free energy that that lowers ΔG‡. F𝚽 is a material specific property that is atypically specified in the rate equation. Because log j0 ∝ - ΔG‡, and chemical free energy F𝚽 lowers ΔG‡, log j0 ∝ F𝚽. Thus, j0 increases exponentially with F𝚽, so PGMs with highest 𝚽 sustain highest j0. Further, the rate expression embeds material specific property 𝚽.The classical Eyring perspective for generic rate constant k’ is k’ = A’ exp[-ΔG‡/RT]. Rate constant is typically determined by varying temperature in a plot of ln k’ versus T-1, where ln k’ = ln A’ - ΔG‡/RT. For isothermal measurements, log j0 is linear with 𝚽 because F𝚽 is a term ΔG‡ chem that is a component in the total ΔG‡. For metals, where 𝚽 > 0, F𝚽 always lowers ΔG‡ for HER; the total activation energy is lowered in proportion to F𝚽. The slopes of log j0 versus 𝚽 is proportional to 𝝰𝚽F𝚽/2.303, where partition coefficient 𝝰𝚽 characterizes ∂ΔG‡/∂𝚽. For the parallel lines in Trasatti’s plot, 𝝰𝚽 = 0.38. The intercepts are independent of 𝚽.The material specific rate expressions derived from classical TST and electrochemical potentials may provide guidance on design of electrocatalysts and provide a path to integration of classical and contemporary modeling of important reaction processes such as HER.