Platinum Group Research Articles

Intramolecular Csp3-H Activation at a Platinum(IV) Center Resulting from O2 Activation: The Role of a Proton-Responsive Ligand and Trans Influence.

Aerobic oxidation of a dimethylplatinum(II) complex featuring 1,1-di(2-pyridyl)ethanol as a supporting ligand leads to the formation of two unexpected PtIV complexes (in ∼1:1 ratio), neither of which results from direct oxidation typical for PtII centers supported by popular κ2-(N,N) ligands. While one product features an isomerized PtIV center stabilized by the κ3-(N,N,O) ligand coordination mode, surprisingly, the other product results from intramolecular activation of the ligand methyl fragment. Mechanistic studies, reactivity of model complexes, and DFT calculations reveal that the critical proton-responsive nature of the ligand allows formation of intermediates that result in a concerted metalation deprotonation (CMD)-like C-H activation at PtIV. To the best of our knowledge, this is the first mechanistic delineation of Csp3-H activation at PtIV, despite being known for other high-valent platinum group metal centers.

Cooperative Atomically Dispersed Fe-N4 and Sn-Nx Moieties for Durable and More Active Oxygen Electroreduction in Fuel Cells.

One grand challenge for deploying porous carbons with embedded metal-nitrogen-carbon (M-N-C) moieties as platinum group metal (PGM)-free electrocatalysts in proton-exchange membrane fuel cells is their fast degradation and inferior activity. Here, we report the modulation of the local environment at Fe-N4 sites via the application of atomic Sn-Nx sites for simultaneously improved durability and activity. We discovered that Sn-Nx sites not only promote the formation of the more stable D2 FeN4C10 sites but also invoke a unique D3 SnNx-FeIIN4 site that is characterized by having atomically dispersed bridged Sn-Nx and Fe-N4. This new D3 site exhibits significantly improved stability against demetalation and several times higher turnover frequency for the oxygen reduction reaction (ORR) due to the shift of the reaction pathway from a single-site associative mechanism to a dual-site dissociative mechanism with the adjacent Sn site facilitating a lower overpotential cleavage of the O-O bond. This mechanism bypasses the formation of the otherwise inevitable intermediate that is responsible for demetalation, where two hydroxyl intermediates bind to one Fe site. As a result, a mesoporous Fe/Sn-PNC catalyst exhibits a positively shifted ORR half-wave potential and more than 50% lower peroxide formation. This, in combination with the stable D3 site and enriched D2 Fe sites, significantly enhanced the catalyst's durability as demonstrated in membrane electrode assemblies using complementary accelerated durability testing protocols.

Three-dimensional nanocomposites derived from combined metal organic frameworks doped with Ce, La, and Cu as a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction

Fabrication of a nanocomposite with a low-cost and efficient synthesis method instead of using electrocatalysts based on platinum metal has become one of the main challenges in energy storage devices and fuel cells. In this regard, a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction is fabricated and tested. The novelty of this study is the synthesis method and enhancement of the electrochemical characteristics of synthesized electrocatalysts. The core-shell method is used for the electrocatalyst's synthesis which uses Zeolitic Imidazolate Framework (ZIF)-8, ZIF-67, and Material Institute Lavoisiers (MIL)-101 for the fabrication of three types of electrocatalysts. In the following, to increase the characteristics such as conductivity and stability, doping of Copper (Cu), Cerium (Ce), and Lanthanum (La) are added to the nanocomposites. The Co@NC, CoZn@NC, and CoZn@FeNC prepared electrocatalysts are obtained from the pyrolyze process of La/ZIF-67, CeCu/ZIF-8@ La/ZIF-67, MIL-101@CeCu/ZIF-8/La/ZIF-67. The results indicated that the CoZn@NC electrocatalyst has the best performance in the oxygen reduction reaction (ORR) with an onset potential of 0.062 (V vs Ag/AgCl) and current density of −12.97 (mA/cm2) at a constant voltage of −1 V. Furthermore, the electron transfer number of CoZn@NC electrocatalyst for ORR was 3.64. The conducted Galvanostatic Charge-Discharge (GCD) tests demonstrated that the CoZn@NC electrode has the highest capacitance of 271.14 F/g. The outcomes showed that by the core-shell method, various properties of nanocomposites can be utilized to solve the weaknesses of catalysts by using proper metals. Moreover, the presence of Cu2+,Ce3+,La3+ improve the structural defects in the carbon matrix, the stability based on the chronoamperometry results, and the mass transfer. The study provides a perspective for future researches to fill the research gaps to obtain the new supercapacitors utilize on a large scale in the electronics industry.

From Exhaust to Extraction: Evaluating Car Catalysts Waste for a Resilient Economy

Spent Automotive Catalytic Converters (SACC) are comprised of a support (a honeycomb ceramic structure) coated with a catalytic layer, where Platinum Group Elements (PGE), especially Pt and Pd, facilitate oxidation and reduction reactions to reduce hazardous emissions from car engines. This study provided information about various measurement procedures and principles for characterising SACC, revealing that SACC can release Potentially Toxic Elements (PTE) under environmental conditions. The SACC samples used primarily contain cordierite and moissanite, likely distinguishable upon visual inspection of waste piles. Unlike geological samples, the SACCs samples, considered as a homogeneous matrix, exhibit major elements such as Al, Si, Mg, and Ba, with minor elements including P, Na, Ca, Fe, Ti, Ce, and Zr, posing challenges for geoanalysts and environmental managers. Sequential extraction demonstrated high concentrations of PGE in the residual phase, especially Pt, Pd, and Rh. All other fractions, oxidisable, reducible and exchangeable, showed significant analytical recoveries of PTE such as Zn, Cu, and other trace elements. Watering bulk samples resulted in exceeded reference thresholds, with high Cd, Ni, and Zn, identifying SACC as a potentially hazardous materials. Toxicity tests on three aquatic species (A. fischeri, R. subcapitata, and D. magna) indicated both acute and chronic effects, further highlighting the need for proper waste management. The characterisation approach suggested here can help define the most appropriate SACC treatment demonstrating economic profit and ecological benefits.

Crystallization behavior of smelting slag for recovery of platinum group metals from spent automotive catalysts and preparation of foamed glass-ceramics

Spent automotive catalysts (SAC), as a significant secondary resource for platinum group metals (PGMs), can be recovered on a large scale through high-temperature smelting. Besides, as a byproduct, the glass slag lacks high-value applications. This paper proposes a recyclable method to convert slag, graphite powder (GP), and ferric oxide (Fe2O3) into foamed glass-ceramics through low-temperature sintering, significantly reducing environmental impacts and production costs. Non-isothermal differential thermal analysis was used to explore the transition and crystallization temperature range, transition kinetic, crystallization kinetic, and crystallization behavior of the glass slag. Furthermore, the influence of the foaming agent composition and heat treatment temperature on the physical properties, chemical resistance, and mechanical properties of the foamed glass-ceramics was investigated. Foamed glass-ceramics composed of 60wt% slag-30wt% Fe2O3-10wt% GP exhibited the excellent properties of a geometric density of 1.43 g/cm3, a volumetric water absorption of 26.32%, a compressive strength of 8.08 MPa, and a mass loss of 3.56% in strong acid and 0.08% in strong alkali after low temperature heat treatment at 1160°C. This study provides an insight into transforming low-value waste into high-performance foamed glass-ceramics.

Oxygen evolution reaction mechanism on platinum dioxide surfaces based on density functional theory calculations

The oxygen evolution reaction (OER) counterbalances the hydrogen evolution reaction (HER) during water dissociation under an electric field. Platinum (Pt) group metals and their oxides exhibit considerable durability as electrocatalysts for water dissociation. However, an atomic-level understanding of the OER on Pt-oxide surfaces at high potential remains elusive because of the limited experimental techniques for tracking dynamic surface species involved in adsorption, electron transfer, or interactions. Herein, the OER mechanisms involving water nucleophilic attack (WNA) and intramolecular oxygen coupling (IMOC) were studied on Pt and platinum dioxide (PtO2) surfaces using density functional theory (DFT) calculations, indicating that the WNA mechanism dominates the OER on Pt and PtO2 electrode surfaces. The OER activity on the PtO2(100) surface is better than the PtO2(111) surface due to the high overpotential obtained on PtO2(111). These findings offer valuable insights into the OER mechanism on oxidized Pt surfaces and suggest new strategies for designing and optimizing Pt-based catalysts for improved stability and performance.

Role of Nano Catalysts In Green Chemistry

Abstract This study explores the role of nano catalysts in enhancing catalytic performance through their unique properties and applications in sustainable chemistry. Nano catalysts, defined as materials operating at the nanometer scale, typically between 1 and 100 nanometers, exhibit significantly increased surface area and altered electronic properties, leading to improved reaction rates and efficiencies. The investigation highlights the critical properties of nano catalysts, such as their high surface area-to-volume ratio, controlled shapes, and tunable surface functionalities, which contribute to their effectiveness in various catalytic processes. Different types of nano catalysts, including metal nanoparticles, metal oxides, and carbon-based nano materials, are examined for their distinct advantages and applications. Metal nanoparticles, like gold and platinum, offer enhanced catalytic activity due to their unique electronic behaviors, while metal oxides, such as titanium dioxide, provide stability in photocatalytic applications. Additionally, carbon-based nano materials, including carbon nanotubes and graphene, are recognized for their exceptional electrical conductivity and surface area, making them suitable for energy conversion and environmental remediation.

A fluorescent probe for selective detection of Pd2+ combined with fluorescent composite membranes and bioimaging

Palladium, as a transition metal of the platinum group elements, plays an indispensable role in chemical, pharmaceutical, and industrial production. However, its potential toxicity can pose risks to our health and the environment. In this work, a novel parallel alkyne-amine naphthalene ring fluorescent probe LNA based on Pd2+ coordination has been developed. The basic structure and detection mechanism of the probe have been confirmed by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and liquid chromatography-mass spectrometry (LC-MS). The probe LNA has a fluorescence-off response to the Pd2+ with high sensitivity (as fast as 60 s) and excellent selectivity (with a detection limit as low as 0.12 μM). Due to the outstanding fluorescence properties of LNA and the low cytotoxicity of its ligand complexes, it has been successfully applied to carboxymethyl cellulose-based fluorescent composite membranes as well as Pd2+ imaging of living cells.

In a search of the single-atom electrocatalysts for hydrogen production: the first sulfur-free mono- and diphenanthrenyl-terminated iron and cobalt(II) clathrochelates versus their thioanalogs

This paper reports on green chemistry approaches to the molecular design and synthesis of cheap, efficient and eco-friendly electrocatalysts of the hydrogen evolution reaction (HER). The title clathrochelates (including first those do not containing sulfur derivatives as “catalytic poisons”) were prepared using nucleophilic substitution of their chloroclathrochelate precursors and characterized by analytical, spectral and XRD methods. These complexes showed the HER 2H+/H2 electrocatalytic activity in the solutions. They form the Langmuir monolayers and possess a high physisorption on activated carbon (AC, up to 0.55mmol·g–1) and reduced graphene oxide (RGO, up to 0.33mmol·g–1). Contrary that on carbon paper (CP) is very low. Therefore, AC- or RGO-containing clathrochelate-immobilized components are suitable for preparation of hybrid CP-based cathodes, allowing to substantially increase a surface concentration of electrocatalytically active centers up to 0.5 μmol·m–2. Cyclic voltammetry data suggest that the electrochemically generated cobalt(I) complexes, as the catalytically active intermediates, are stable and most prospective candidates for electrocatalytic hydrogen production. Clathrochelate-based single-atom catalysts were prepared in accordance with basic principles of green chemistry. They are derivatives of abundant and cheap 3d-biometals and low-toxic α-dioximes and possess an extremely high atomic utilization efficiency matching the “economy of atoms” principle. Nowadays, the carbon-supported metallic platinum is used as HER catalyst. The reserves of this noble and expensive metal on the Earth are limited and its replacement by such cheap and abundant HER materials will accelerate the development and implementation of green hydrogen-producing technologies. The recommendations on chemical structures of optimal molecular electrocatalysts were evaluated.

Highly Efficient and Durable Water Electrolysis at High KOH Concentration Enabled by Cationic Group-Free Ion Solvating Membranes in Free-standing Gel Form.

The degradation of fixed cationic groups in most anion exchange membranes (AEMs) under alkaline environments limits their durability for alkaline water electrolysis (AWE). Ion-solvating membranes (ISMs) have emerged as a promising alternative to address this issue. Herein, a cationic group-free ion solvating membrane in a free-standing gel form (ISM-PBI-FG) is presented, created through a sol-to-gel transformation process followed by KOH imbibing. This approach yields a 3D porous microstructure composed of entangled polybenzimidazole (PBI) nanofibrils, achieving 89% porosity, which enables ultrahigh alkali uptake (346% in 6 M KOH) and exceptional ionic conductivity (763 mS cm-1 at 80 °C). The absence of cationic groups avoids the attack by OH-, thus ensures good alkaline stability with a conductivity retention rate of 91.6% over a 3120 h ex situ test in 6 M KOH. The resulting membrane delivered outstanding AWE performance with current densities of 5.5 A cm-2 using platinum-group-metal (PGM) catalysts and 2.2 A cm-2 using PGM-free catalysts at 2.0 V. Notably, the in situ electrolyzer device based on ISM-PBI-FG offers extensive operational flexibility ranging from 40-100 °C and demonstrates record durability in concentrated alkaline conditions, with a voltage decay rate of only 23.5µVh-1, outperforming most reported AEMs and ISMs.

Oxidation of Ni(H2O)6@MoO3 to Ni2O3/MoO3 Composites by Aerial Annealing: Electrocatalytic Hydrogen Evolution.

Molybdenum trioxide (α-MoO3) is a promising and inexpensive alternative to platinum group metals (PGMs), for electrocatalytic hydrogen evolution reaction (HER). However, to make it a viable candidate for electrocatalytic systems, we must address the hurdles associated with its inferior electrical conductivity and lack of active sites. Unlike Mo-based compounds such as MoS2 and MoSe2, which possess catalytically active edges, α-MoO3 lacks inherent active sites for HER. Previous studies have employed various strategies to activate MoO3 for HER, yet its activation in near-neutral conditions remain largely unexplored. In this study, a previously known α-MoO3 intercalating {Ni(H2O)6}2+, [MoVI2O6(CH3COO){NiII(H2O)6}0.5]·H2O (Ni(H2O)6@MoO3) is prepared via a simple and scalable room-temperature aqueous synthesis. In the subsequent aerial thermal annealing process at 300, 400 and 500 °C, Ni(H2O)6@MoO3 acts as a self-sacrificial template, yielding mixed metal oxide composites of nickel and molybdenum (named as MoO3-300, MoO3-400 and MoO3-500). The HR-TEM and XPS analyses confirm the formation of the Ni2O3 phase alongside the orthorhombic α-MoO3. The annealing temperature plays a key role in the crystallinity, phase, morphology, and electrocatalytic performance of the resulting composites. The composite formed at 400 °C (MoO3-400) shows the best electrocatalytic performance among them.

Synthesis of Bis(diimino)palladium Nanosheets as Highly Active Electrocatalysts for Hydrogen Evolution.

Development of efficient electrocatalysts for hydrogen evolution reactions (HERs) is necessary to achieve environmentally friendly and sustainable hydrogen production. To reduce cost and to circumvent the scarcity of platinum, the most efficient catalyst for HER, it is essential to develop catalysts using ubiquitous base metals or minimal amounts of precious noble metals. Bis(diimino)metal (MDI) coordination nanosheets are potential HER catalysts because their electric conductivities, two-dimensionality, and porous structures provide large surface areas and efficient mass and electron transfer. In addition, with sparse metal arrangements in their chemical structures, nanosheets can reduce the amount of metal needed. We synthesized bis(diimino)palladium coordination nanosheets (PdDI) as a coordination polymer composed of bis(diimino)palladium, with semiconducting characteristics, using gas-liquid interfacial synthesis and electrochemical oxidation. These electrochemically synthesized PdDIs exhibit remarkable catalytic performance with overpotential reaching 10 mA cm-2 of 34 mV, a Tafel slope of 47 mV dec-1, and an exchange current density of 2.1 mA cm-2 after appropriate activation. This performance is closely comparable to that of metallic platinum. An ex-situ investigation of the activation process revealed that reduction of the divalent Pd center in bis(diimino)palladium produced a composite of Pd(0) species and PdDI, combining high catalytic activity with smooth electron transfer.

Recent depositional history of noble and critical elements in sediments from a wastewater-impacted bay (Vidy Bay, Lake Geneva, Switzerland)

Opposing trends in environmental pollution have been observed in recent years, with a growing awareness of the need to reduce emissions to the environment being accompanied by a concomitant increase in the use of polluting substances, which can potentially end up in the environment and harm humans and ecosystems. In order to assess the temporal evolution of loadings of seldom monitored trace elements, including noble metals and some technology critical elements, we analyzed a sediment core taken from the Bay of Vidy (Lake Geneva), impacted by the effluent of an urban wastewater treatment plant (WWTP). The temporal profiles of the chemical elements show essentially two patterns linked to the implementation of the WWTP, with some elements increasing sharply (e.g. Au, In, Ba, Sb, Sn, platinum group elements), while others (e.g. Ga, Ge, rare earth elements) show decreasing concentrations due to dilution by additional effluent particle loads. The origin of the elements showing a marked increase is attributed to local sources (photographic industry and municipal incinerator). There is (still?) no evidence in the sedimentary record of concentration increases linked to the growing use of technologically critical elements by industry.

Moratorium? Youth experiences of waiting on South Africa’s ‘platinum belt’

ABSTRACT The extraction of platinum group metals in South Africa's rural territories has increased the hope for development and employment opportunities among local residents. However, despite the increase in mining activities over the past decades, poverty and unemployment persist. Drawing on detailed ethnographic research conducted in a platinum-rich community on South Africa's rural ‘platinum belt' – the Bafokeng – this article explores the experiences of unemployment and waiting among the local youth. Recent studies have highlighted the active agency of unemployed youth in devising and deploying strategies to engage with local and outside structural forces of waiting. The analysis, however, reveals the complex power relations in the local social landscape. The article shows that deliberate actions by platinum mining corporates working in cahoots with the traditional authorities (the chiefs) in the Bafokeng community result in the ‘social moratorium’ of the youth.

A Chalcogenide-Derived NiFe2O4 as Highly Efficient and Stable Anode for Anion Exchange Membrane Water Electrolysis.

Developing low-cost, highly active, and durable oxygen evolution reaction (OER) electrodes is one of the critical scientific issues for anion exchange membrane water electrolyzer (AEM-WE). Herein, we report a vacancy-rich and alkali-stable NiFe2O4-type electrode (named as NiFeOx-350-Ov), derived from the chemical-vapor deposited precursor NiFeSexSy-350, as an efficient and robust anode material. The obtained electrode affords current densities of 100 and 500 mA cm-2 at overpotentials of 245 and 270 mV, respectively, and displays excellent long-term durability sustaining 1.0 A cm-2 at least for 1000 h. When coupled with Ni4Mo/MoO2/NF as a hydrogen evolution reaction (HER) catalyst, the resulting platinum-group metal (PGM)-free single-cell AEM-WE exhibits a cell voltage of 1.71 V at the current density of 1000 mA cm-2 at 80 °C and long-term durability during a current-cycling test between 0.5 A cm-2 and 1.0 A cm-2 over 150 h at 60 °C. This work highlights a unique reconstruction strategy for preparing highly active and durable OER catalysts used in PGM-free AEM-WE.

Insight Into Intermediate Behaviors and Design Strategies of Platinum Group Metal-Based Alkaline Hydrogen Oxidation Catalysts.

Hydrogen oxidation reaction (HOR) can effectively convert the hydrogen energy through the hydrogen fuel cells, which plays an increasingly important role in the renewable hydrogen cycle. Nevertheless, when the electrolyte pH changes from acid to base, even with platinum group metal (PGM) catalysts, the HOR kinetics declines with several orders of magnitude. More critically, the pivotal role of reaction intermediates and interfacial environment during intermediate behaviors on alkaline HOR remains controversial. Therefore, exploring the exceptional PGM-based alkaline HOR electrocatalysts and identifying the reaction mechanism are indispensable for promoting the commercial development of hydrogen fuel cells. Consequently, the fundamental understanding of the HOR mechanism is first introduced, with emphases on the adsorption/desorption process of distinct reactive intermediates and the interfacial structure during catalytic process. Subsequently, with the guidance of reaction mechanism, the latest advances in the rational design of advanced PGM-based (Pt, Pd, Ir, Ru, Rh-based) alkaline HOR catalysts are discussed, focusing on the correlation between the intermediate behaviors and the electrocatalytic performance. Finally, given that the challenges standing in the development of the alkaline HOR, the prospect for the rational catalysts design and thorough mechanism investigation towards alkaline HOR are emphatically proposed.

Investigations on symbol regression for improving the prediction accuracy of gas-metal adsorption energies in machine learning

Adsorption energy plays a crucial role in surface catalytic reactions and influences the performance of the catalysts. Machine learning offers a novel approach for the computation of adsorption energy. The selection of a crystal plane is critical for the calculation of the adsorption energy, with current research focusing on low-index crystal planes. The prediction of catalytic performance is challenging because of the complexity arising from the surface reactions occurring on multiple crystal planes. However, this challenge can be resolved by introducing effective descriptors and utilizing advanced machine learning methods. This study collected data from various sources, such as databases, literature, and Density Functional Theory calculations, and utilized machine learning to predict the adsorption energies of prevalent adsorbates on multiple crystal planes of several platinum group metals in catalytic reactions. New structural descriptors were developed by leveraging the expertise of material researchers, and feature engineering techniques were employed to improve the predictive accuracy of the machine learning model. To prevent data loss and detect potential regularities, new features are created using symbolic regression. The introduction of these new features significantly enhanced the model's performance, increasing R2 from 0.885 to 0.921, and providing innovative concepts for future catalyst design.

Improved Oxygen Reduction Reaction Activity of Graphene via Mechanochemical Activation and Halogen‐Doping

AbstractThere has been an increased effort to replace the expensive and rare platinum and platinum group metals to speed up the sluggish oxygen reduction reaction (ORR) kinetics, which limits the efficiency of fuel cells. One class of promising Pt‐alternative catalysts for ORR is metal‐free halogen‐doped carbon materials. Herein, bromine‐doped and iodine‐doped graphene were synthesized via mechanochemical activation. The synthesized samples exhibited sub‐rounded particles. Mechanical activation via ball milling increased the specific surface area of graphene by reducing particle size. Ball milling also enhanced dopant dispersibility and increased surface roughness, though it reduced surface area compared to ball‐milled graphene, likely due to the size difference between carbon and halogen atoms. Among the synthesized catalysts, iodine‐doped graphene exhibits the highest limiting current density of 1.806 mA cm−2 with the highest ORR onset potential of 0.74 V vs reversible hydrogen electrode (RHE). The iodine‐doped graphene also showed good stability after 1000 cycles of accelerated degradation test. The enhanced ORR performance of iodine‐doped graphene was reached using the optimized iodine‐to‐graphene mass ratio of 4 : 1 after 48 h ball milling time.

Bimetallic organic framework derived Co-MoxN/Mo2C catalyst for HER/OER bifunctional electrocatalytic reaction

Metal organic frameworks (MOFs) are widely used as precursors due to their tunable morphology and high specific surface area. Molybdenum nitride (MoN) and molybdenum carbide (Mo2C) are promising catalyst materials with electronic structures similar to the noble metal platinum. However, the preparation and modification of the composite systems comprising MoN and Mo2C are complex, often leading to significant agglomeration and limiting their application in various catalytic fields. In this work, we designed and developed a novel bimetallic Co-MOFs-Mo with a stable and unique framework morphology. By varying the organic ligand content, we controlled the morphology and enhanced the intrinsic electrocatalytic activity through Mo doping. Using the Co-MOFs-Mo sample as the Co source, we fabricated a Co-MoxN/Mo2C catalytic material with a special framework structure. Compared to Mo2N and Mo2N/Mo2C, this catalyst exhibits a larger specific surface area and superior performance in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Co-MoxN/Mo2C catalyst achieves an HER overpotential of 297 mV at a current density of 10 mA·cm−2 and an OER overpotential of 480 mV at 20 mA·cm−2. This research provides valuable insights into the rational design of molybdenum-based noble-metal-free catalyst materials.

Determination of Osmium and other Platinum Group Elements in Active Pharmaceutical Ingredients by ICP-MS

Determination of Osmium and other Platinum Group Elements in Active Pharmaceutical Ingredients by ICP-MS