Pt-Rh Alloy Research Articles

Electronegativity Induced d‐Band Center Offset for Pt‐Rh Dual Sites in High‐Entropy Alloy Boosts Liquid Fuels Electrooxidation

AbstractInvestigating the catalytic behavior of the liquid fuels on well‐defined dual sites is crucial in understanding electrocatalytic reactions. Herein, concept holding bidirectional electronegativity dominant d‐band center regulation on Pt‐Rh dual sites is proposed to tailor the catalytic behaviors toward methanol oxidation reaction (MOR). The Pt‐Rh dual sites are engineered by introducing the low‐electronegativity Ga/Ni and high‐electronegativity W elements in PtRhGaNiW high‐entropy alloy (HEA), which can drive the electron cloud of Pt‐Rh dual sites redispersing over a wide orbit window. The optimized Pt‐Rh dual sites in PtRhGaNiW HEA nanowire achieve a high current density of 5.61 mA cm−2 toward MOR, which is 3.38 and 9.75 times than that of PtRh alloy (1.66 mA cm−2) and Pt/C (0.57 mA cm−2), as well as remarkably stability and COads poisonous resistance. The theoretical calculations further disclose that the redistribution of surface localized electron around Pt‐Rh dual sites can promote direct oxidation of ─OH, and accelerate the COads oxidation/removal. This work presents a breakthrough in designing advanced dual site electrocatalysts for complex catalytic reactions.

Towards High-Temperature MEMS: Two-Step Annealing Suppressed Recrystallization in Thin Multilayer Pt-Rh/Zr Films.

Platinum-based thin films are widely used to create microelectronic devices operating at temperatures above 500 °C. One of the most effective ways to increase the high-temperature stability of platinum-based films involves incorporating refractory metal oxides (e.g., ZrO2, HfO2). In such structures, refractory oxide is located along the metal grain boundaries and hinders the mobility of Pt atoms. However, the effect of annealing conditions on the morphology and functional properties of such multiphase systems is rarely studied. Here, we show that the two-step annealing of 250-nm-thick Pt-Rh/Zr multilayer films instead of the widely used isothermal annealing leads to a more uniform film morphology without voids and hillocks. The composition and morphology of as-deposited and annealed films were investigated using X-ray diffraction and scanning electron microscopy, combined with energy-dispersive X-ray spectroscopy. At the first annealing step at 450 °C, zirconium oxidation was observed. The second high-temperature annealing at 800-1000 °C resulted in the recrystallization of the Pt-Rh alloy. In comparison to the one-step annealing of Pt-Rh and Pt-Rh/Zr films, after two-step annealing, the metal phase in the Pt-Rh/Zr films has a smaller grain size and a less pronounced texture in the <111> direction, manifesting enhanced high-temperature stability. After two-step annealing at 450/900 °C, the Pt-Rh/Zr thin film possessed a grain size of 60 ± 27 nm and a resistivity of 17 × 10-6 Ω·m. The proposed annealing protocol can be used to create thin-film MEMS devices for operation at elevated temperatures, e.g., microheater-based gas sensors.

Intensification of opening a thrust alloy based on platinum and rhodium

A high chemical resistance inherent in the alloys based on platinum group metals is one of the reasons for a number of difficulties that arise when dissolving such materials. Nowadays, the dissolution in aqua regia is one of the most effective methods for dissolving corrosion-resistant alloys. The main disadvantage of this method is a release of toxic gaseous substances such as nitrosyl chloride and nitrogen oxides. To decrease the volume of gases thus released without reducing the redox potential of the system, we proposed a method of dissolving a Pt – Rh alloy in HCl-HNO3 with a controlled dosed supply of HNO3 at a given value of the oxidation-reduction potential (ORP) of the system. The potential of the system has been chosen proceeding from the potential for HNO3 – HCl – Pt and HNO3 – HCl-Rh systems and amounted to 0.85 and 0.9 V. The impact of the dispersion and the inherent flaw of PtRh alloys on the dissolution indices of the alloy was also considered. It is shown that the dissolution of a Pt – Rh alloy with a rhodium content of 15 % in HCl – HNO3 at a constant value of ORP = 0.9 V compared to the use of the classic mixture (HCl:HNO3 = 1:3 vol.) provides a decrease in nitric acid consumption by 40%, reduction of the process time, increase in the recovery factor for both platinum and rhodium, and a two-fold reduction of the volume of released nitrogen oxides (theoretical calculation). It is also revealed that the process of mechanical activation of the alloy reduces the dissolution time and leads to almost quantitative dissolution of the sample.

Exploring the Impact of Zirconium Doping on the Mechanical and Thermodynamic Characteristics of Pt-40Rh Alloy through First-Principles Calculations

Zirconium (Zr) element doping has proven to be an effective strategy for reinforcing the strength and toughness of Pt-Rh alloys. However, the incorporation of Zr into Pt-Rh alloy in solid solution form renders its microstructural observation challenging through experimental means, thus complicating the elucidation of its underlying mechanisms. Therefore, this study employs density functional theory-based first-principles calculations to investigate the mechanical and thermodynamic properties of Pt-40Rh-xZr (x = 0, 0.1, 0.5, 1.0) alloys. The results reveal that with an increasing Zr weight percentage, Young’s modulus, and hardness of Pt-40Rh-xZr alloys exhibit a trend of an initial decrease followed by a subsequent increase. Notably, at a Zr weight percentage of 1.0 wt.%, the alloy Pt-40Rh-1.0Zr demonstrates the highest Young’s modulus (329.119 GPa) and hardness (10.590 GPa). Concurrently, thermodynamic calculations indicate that as Zr content increases, the crystal thermal stability of Pt-40Rh-xZr alloys initially decreases before rising again. More specifically, the coefficient of thermal expansion for Pt-40Rh-1.0Zr is merely 89.518% of that observed in Pt-40Rh. These results imply that incorporating 1.0 wt.% Zr results in the most substantial enhancement in the comprehensive mechanical properties of the Pt-40Rh-xZr alloy. Consequently, this study offers theoretical insights that can guide the extended application of Pt-Rh alloys.

Understanding the nature of Pt-Rh synergy for three-way conversion catalysis

A series of Al2O3 supported Pt, Rh and Pt-Rh catalysts was investigated for TWC catalysis. Profound synergy between Pt and Rh was found on all Pt-Rh compositions relative to their single metal references with significantly reduced light-off temperatures. The nature of this synergy was probed using various characterization techniques. CO chemisorption, CO-DRIFTS and XPS results show that the surface Rh concentrations on aged Pt-Rh catalysts are much higher than that of the Rh reference. In addition, on the bimetallic catalysts the Rh species is in a more reduced state as indicated by XPS and XANES. AC-STEM/EDS results clearly illustrate that there are two types of Rh species on an aged Pt-Rh catalyst in terms of its location: one sitting on Pt particles as Rh nanoparticles and the other associated with the Al2O3 support as sub-nano Rh moieties. The Pt-Rh bimetallic particles contain a certain degree of Pt-Rh alloy as evidenced by the upshift of the metal XRD peaks and the Pt-Rh coordination from the EXAFS measurement. All structural and microscopy analyses suggest that Rh is surface enriched on the Pt-Rh particles, and it is the surface enriched Rh species that plays a primary role in enhancing the activity of Pt-Rh catalysts.

Structural and elastic properties of binary FCC Pt-Rh alloys – a first-principles study

Alloying Pt with Rh significantly enhances the high temperature stress rupture strength and maintains both oxidation and corrosion resistance at elevated temperatures. Such unique property combination renders Pt-Rh alloys mainstay in space technology, glass and chemical industries. However, the exponential increase in the price of Rh in the past few years stirs an industrial concern. As a result, some industries are beginning to search for alternative alloys that can offer similar properties. This study conducted first-principles calculations to generate structural and elasticity data on binary Pt-Rh alloys using both supercell and virtual crystal approximation (VCA) approaches, to serve as a benchmark for new alternative Pt-based alloys.

Soluble porous organic cages as homogenizers and electron-acceptors for homogenization of heterogeneous alloy nanoparticle catalysts with enhanced catalytic activity

The creation of ultrafine alloy nanoparticles (<5 nm) that can maintain surface activity and avoid aggregation for heterogeneous catalysis has received much attention and is extremely challenging. Here, ultrafine PtRh alloy nanoparticles imprisoned by the cavities of reduced chiral covalent imine cage (PtRh@RCC3) are prepared successfully by an organic molecular cage (OMC) confinement strategy, while the soluble RCC3 can act as a homogenizer to homogenize the heterogeneous PtRh alloy in solution. Moreover, the X-ray absorption near-edge structure (XANES) results show that the RCC3 can act as an electron-acceptor to withdraw electrons from Pt, leading to the formation of higher valence Pt atoms, which is beneficial to improving the catalytic activity for the reduction of 4-nitrophenol. Attributed to the synergistic effect of Pt/Rh atoms and the unique function of the RCC3, the reaction rate constants of Pt1Rh16@RCC3 are 49.6, 8.2, and 5.5 times than those of the Pt1Rh16 bulk, Pt@RCC3 and Rh@RCC3, respectively. This work provides a feasible strategy to homogenize heterogeneous alloy nanoparticle catalysts in solution, showing huge potential for advanced catalytic application.

A promising layered thermoelectric metallic ceramic with ultra-high temperature stability: Mo2Ti2AlC3

As a structural ceramic, MAX phases have attracted the most attentions because of light weight, excellent machinability, good thermal shock resistance and thermal stability at ultra-high temperature. Herein, for the first time we reported the thermoelectric property of Mo2Ti2AlC3, one of MAX phases. It has similar resistivity (~2.3 μΩ·m) and higher Seebeck coefficient (−15μV/K) compared with Pt-Rh alloy. Mo2Ti2AlC3 has higher power factor (~46% improvement) and much lower thermal conductivity (6.2 W/(m·K), one-third) compared with SiC thermoelectric ceramics at 700 °C. The ZT value is about 0.0138 at 700 °C, which is three times as high as that of SiC-7%Si3N4 thermoelectric composite. These suggest that Mo2Ti2AlC3 and other MAX phases have an important application prospect in the field of thermoelectric generator and temperature sensor at ultra-high temperature. Meanwhile, although Mo2Ti2AlC3 ceramic shows metallic transport behavior, the electric thermal conductivity far deviates from traditional Wiedemann-Franz law, indicating that there are strong correlations or couplings between electrons and 2-D layered lattices, and Mo2Ti2AlC3 is a new strong related system with spin-orbital coupling.

Coating PtRh alloy nanoparticles with mesoporous silica for the hydrogenation of toluene to methylcyclohexane

Coating PtRh alloy nanoparticles with mesoporous silica for the hydrogenation of toluene to methylcyclohexane

Study on Heating Uniformity of Pt-Rh Alloy Bushing for Producing Flexible Glass

Study on Heating Uniformity of Pt-Rh Alloy Bushing for Producing Flexible Glass

Structural Evolution of a PtRh Nanodendrite Electrocatalyst and Its Ultrahigh Durability toward Oxygen Reduction Reaction

Durable Pt-based electrocatalysts toward oxygen reduction reaction (ORR) are essential preconditions for the commercialization of proton-exchange membrane fuel cells. However, dissolution of metal components as one major cause of the degradation of the Pt-based electrocatalysts has not yet been fully ameliorated in engineering aspects until now. Here, we report an ultradurable PtRh nanodendrite (PtRh ND) electrocatalyst, with remarkable 88% of mass activity retained after an accelerated durability test for 90,000 cycles. Experimental results demonstrate an intense structural evolution of the PtRh NDs and consequently the formation of a Pt-rich surface during the initial potential cycling, and this newly formed structure has strong resistance to dissolution. Density functional theory calculations reveal a “self-healing” effect that the difference in the dissolution energy of Pt and Rh atoms leads to this structural evolution. Besides, the synergy effect of the Pt-rich surface and the inner PtRh alloy suppresses the further dissolution of metal components and thus endow the catalyst with ultrahigh durability. The findings in this work provide inspirations for better designs of highly stable Pt-based ORR electrocatalysts.

Phase transitions during solid-phase sintering of WC-Co(8%)

In this study, the hardmetal powder (WC-Co(8%)), consisting of refractory tungsten carbide (WC) and cobalt (Co) powders (8%), is investigated in order to determine its phase transitions under conditions close to traditional solid-phase sintering at 1450 ○C. Quantitative composition of the WC-Co(8%), WC, Co powders was performed using X-ray microanalysis. The powder’s phase analysis and thermal analysis were conducted using X-ray diffraction and thermogravimetric thermal analysis (TGA)/differential thermal analysis (DTA). Thermal analysis was carried out in an inert argon atmosphere on corundum and platinum-rhodium crucibles with a heating rate of 10 ○C / min. It was found that WC-Co (8%) consists of WC as the primary phase, W2C and α, β - phases of Co as impurities. The thermal analysis revealed an exothermic peak within 250-850 ○C with an increasing mass curve. So, thermal and phase analysis of WC-Co (8%), WC-WC and Co powders after heated to 1450○C makes it possible to establish that Co reacts with crucibles during heated WC-Co (8%) powder made of Al2O and PtRh alloys.

Highly corrosion resistant platinum-rhodium alloy coating and its photocatalytic activity

A method of electroplating a platinum–rhodium (Pt-Rh) alloy coating with a specified composition on a metal substrate stainless steel (SS304) is presented in this article. The Pt-Rh bath consists of [Pt (NH3)2]HPO4, H2SO4 and Rh2(SO4)3. The Pt-Rh alloy electrodeposition coatings were characterized by different analytical methods such as Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). SEM images justify that coating is uniform in a 75% duty cycle. Energy Dispersive X-Ray Spectroscopy (EDX) confirms the presence of Pt and Rh in the coating. XRD confirms that crystalline size was reduced from 75% duty cycle to the rest of the PC’s coatings and DC (Direct current). The incorporation of the Pt-Rh metal ions was verified by EDX analyses. The corrosion behaviour of the developed Pt-Rh alloy coatings was evaluated in 0.1 M Na2SO4 solution using potentiodynamic polarization and electrochemical impedance techniques. The coating developed at PC-75% duty cycle possesses the highest corrosion resistance. A photocatalytic degradation study of Pt-Rh coating was conducted for Methylene Blue (MB) dyes under UV light radiation. The dye removal efficiency of Pt-Rh coated samples was 97% after irradiation and PC 75% duty cycles showed an exceptional dye degradation percentage compare to the DC coating source. All photocatalytic behaviour was controlled by using a UV–Vis spectrophotometer.

How Surface Species Drive Product Distribution during Ammonia Oxidation: An STM and Operando APXPS Study

The oxidation of ammonia is a key reaction for the production of artificial fertilizers and for environmental protection. Depending on the area of application, the catalytic reaction needs to be tuned toward the production of either N2 or NO, and this selectivity is controlled by temperature, pressure, reactant ratio, and the type of catalyst. PtRh alloys are highly useful catalytic materials for the oxidation of ammonia, and they can be employed at different reaction conditions. In contrast to pure Pt and Rh catalysts, for which a large number of studies of ammonia oxidation reaction mechanism are available, for PtRh alloys, direct spectroscopic evidence for structure–performance relationship is still lacking. To understand the behavior of PtRh alloys, namely, what is their active phase under reaction conditions and how the alloy composition leads to a particular product distribution, we study the oxidation of ammonia over PtRh/Pt(111) surfaces by simultaneous operando ambient pressure X-ray photoelectron spectroscopy and mass spectrometry at 1 mbar total reaction pressure. These data are complemented by a catalyst surface characterization by scanning tunneling microscopy in ultrahigh vacuum. We establish that the predominant surface structure during NH3 oxidation strongly depends on the degree of Pt enrichment and the O2/NH3 mixing ratio. At the nanoscale, the selectivity toward N2 or NO production is driven by the surface populations of N and O species. These, in turn, are controlled by the nature of the alloying of Pt with Rh.

Composition dependence of spin–orbit torques in PtRh/ferromagnet heterostructures

We experimentally study the spin–orbit torque (SOT) in PtRh/heterostructures by varying the composition of PtRh alloy. By performing dc-biased spin-torque ferromagnetic resonance and second-harmonic measurements in PtxRh1−x/ferromagnet heterostructures, we find that the effective damping-like spin-torque efficiency and spin Hall conductivity are 0.18 and 3.8 × 105 ℏ/2e Ω−1 m−1 for Pt0.9Rh0.1, respectively, with a low resistivity of 46.9 µΩ cm. Furthermore, current induced SOT switching in PtRh/Co is investigated. The critical current density for SOT switching decreases with an increase in the Rh composition of the PtRh alloy, which can be understood by domain wall assisted switching. Due to a large spin Hall conductivity, a relatively low resistivity, and sustainability of the high temperature process, the PtRh alloy could be an attractive spin source for SOT applications.

Facile One-Pot Synthesis of a PtRh Alloy Decorated on Ag Nanocubes as a Trimetallic Core–Shell Catalyst for Boosting Methanol Oxidation Reaction

The development of highly active and stable catalysts is a critical challenge which affects the practical application of the direct methanol fuel cells. Alloying Pt with other metals is an effectiv...

Microhotplates based on Pt and Pt-Rh films: The impact of composition, structure, and thermal treatment on functional properties

Recent progress in portable semiconductor and thermocatalytic gas sensors requires the development of the microhotplates with reduced power consumption, increased shock resistance, and low resistance drift. Rh is known as alloying component, which allows one to decrease the diffusion mobility of Pt in bulk resistive heating elements. Here, a comparison study on the stability of microhotplates based on Pt and Pt-Rh thin films is performed. The porous anodic alumina is used as a substrate, which provides high adhesion of the metal film and the thermal expansion coefficient compatible with Pt and Pt-Rh alloys. Morphology and crystal structure of metal films are studied after recrystallization annealing in air at the temperatures 600–810 °C. To simulate thermal effects of the microhotplates, a model based on the finite element method is developed. The perspectives of Pt-11 % Rh alloy as a material for microhotplates operating at the temperatures above 500 °C are discussed. The achieved characteristics of the fabricated Pt-Rh microhotplates on porous anodic alumina substrates allow one to use them as a universal platform for semiconductor and thermocatalytic gas sensors manufacturing.

IUPAC/CITAC Guide: Evaluation of risks of false decisions in conformity assessment of a multicomponent material or object due to measurement uncertainty (IUPAC Technical Report)

Abstract Risks of a false decision on conformity of the chemical composition of a multicomponent material or object due to measurement uncertainty are defined using the Bayesian approach. Even if the conformity assessment for each particular component of a material is successful, the total probability of a false decision (total consumer’s risk or producer’s risk) concerning the material as a whole might still be significant. This is related to the specific batch, lot, sample, environmental compartment, or other item of material or object (specific consumer’s and producer’s risks), or to a population of these items (global consumer’s and producer’s risks). A model of the total probability of such false decisions for cases of independent actual (‘true’) concentrations or contents of the components and the corresponding measurement results is formulated based on the law of total probability. It is shown that the total risk can be evaluated as a combination of the particular risks in the conformity assessment of components of the item. For a more complicated task, i.e. for a larger number of components under control, the total risk is greater. When the actual values of the components’ concentrations or contents, as well as the measurement results, are correlated, they are modelled by multivariate distributions. Then, a total global risk of a false decision on the material conformity is evaluated by the calculation of integrals of corresponding joint probability density function. A total specific risk can be evaluated as the joint posterior cumulative function of actual property values of a specific item lying outside the multivariate specification (tolerance) domain when the vector of measured values obtained for the item is inside this domain. The effect of correlation on the risk is not easily predictable. Examples of the evaluation of risks are provided for conformity assessment of denatured alcohols, total suspended particulate matter in ambient air, a cold/flu medication, and a PtRh alloy.

Evolution of composition and structure of PtRh/C in the acidic methanol electrooxidation process

PtRh alloys are highly active in the anodic methanol oxidation reaction (MOR) but few studies have looked at their evolution in the composition and structure during the catalytic process. Herein, a uniformly dispersed carbon-supported PtRh (PtRh/C) catalyst with Rh-enriched surface was synthesized via a facial hydrothermal method. By recording the performance of different cyclic voltammetry (CV) cycles during electrocatalytic MOR process in acid, the evolution of PtRh/C in composition and structure was elucidated. During the first 80 CV cycles, the rapid dissolution of the surface Rh atoms and the exposure of active Pt sites lead to the dramatic enhancement of the current density. When further continue the CV cycling, Pt atoms on the surface have aggregated and recombined to form a tightly aligned Pt-enriched surface. But Rh tends to be stable and catalytic performance reaches a relatively stable status with slightly decreased activity. Compared with the performance of PtRu/C catalyst, it can be concluded that PtRh/C has better stability and higher activity based on the less soluble property of Rh than Ru.

Supporting PtRh alloy nanoparticle catalysts by electrodeposition on carbon paper for the ethanol electrooxidation in acidic medium

Pt80Rh20 and Pt60Rh40 alloy catalysts were electrodeposited at constant current density from different electrolytic baths on commercial carbon paper in order to be tested for the ethanol oxidation reaction (EOR) and as anodes in a direct ethanol fuel cell (DEFC). Pt and Rh anodes prepared in the same form were also examined for comparison. As measured by energy-dispersive X-ray microanalyses, the electrodeposited Pt:Rh atomic ratios were the same as those of the precursors in the bath. X-ray diffraction showed the PtRh alloy formation with mean particle sizes of 8.3 and 7.0 nm for Pt80Rh20 and Pt60Rh40, respectively, and a Pt lattice contraction caused by the Rh addition. The X-ray photoelectron spectroscopy analyses suggested a Pt lattice strain due to Rh alloying because the Pt4f binding energies were shifted to higher values with respect to that of pure Pt. The onset potentials of the alloy oxidation, CO stripping and ethanol oxidation in the cyclic and linear sweep voltammograms indicated that Pt60Rh40 was the most active for the CO and the ethanol electrooxidation. The apparent activation energies for the EOR on that alloy were also the lowest one, in agreement with its highest activity. These results were explained by the bifunctional mechanism, assuming that Rh contributed with hydroxylated species to favor the removal of the CO-type adsorbed species on Pt sites, and by the effect of Rh on the Pt electronic structure, the lattice strain being dominating over the charge transfer between Rh and Pt. Tests carried out in single DEFCs showed the feasibility of using the Pt60Rh40 electrodeposited electrodes on carbon as the anode in a real fuel cell environment.