Platinum Alloys Research Articles

Exploring a Facile Synthetic Procedure of Iron-Based Platinum Group Metal-Free Electrocatalyst for Polymer Electrolyte Fuel Cells

The transportation sector, mainly powered by fossil fuels, is responsible for approximately 14% of all greenhouse gas emissions1. Polymer electrolyte fuel cells (PEFCs) are promising candidates for sustainable transport as they only emit water, can be refilled fast, and enable long ranges with a single refill. Their current costs and dependence on scarce materials challenge their broad implementation in heavy-duty vehicles and maritime transportation 2. Another challenge is the catalyst degradation during operation, therefore the goal of at least 35,000 lifetime hours for heavy-duty transportation is ambitious as existing fuel cell vehicles have been engineered for ca. 5,000 hours3. The state-of-the-art catalyst layers are based on platinum nanoparticles supported on carbon and global efforts have been made to develop high-activity catalysts with reduced platinum contents, including platinum alloys such as Pt-Ni4 and Pt-Co5, alternative supports such as nanotubes6, or a combination aforementioned methods. While platinum-based materials remain the most active for the oxygen reduction reaction, their elevated cost and instability during operation motivate the exploration of alternative materials.Platinum group metal (PGM)-free catalysts have gained prominence in the PEFCs field, where Fe-N-C based catalysts have shown high oxygen reduction reaction activity in acidic media7, approaching that of platinum-based catalyst layers, yet their practical application is hindered by insufficient stability under operating conditions8. Inspired by recent efforts7,8, our goal is to develop stable, active, and low-cost catalyst layers using earth-abundant materials. In this poster presentation, I will discuss my efforts in the synthesis of Fe-N-C catalysts by the incorporation of iron in a calcinated nitrogen-doped zeolitic imidazolate framework (ZIF). ZIFs are excellent supports due to their high porosity of approximately 60% and a surface area of 1600 m2/g, leading to a high density of active sites9. After the incorporation of iron, post-treatments are applied including leaching and the utilization of secondary nitrogen precursors, where efforts are made to develop non-hazardous activation approaches. The incorporation of secondary nitrogen precursors such as cyanamide have been shown to promote the formation of metal-N-C bonds and increase the performance towards the oxygen reduction reaction10,11. We employ microscopic, spectroscopic and electrochemical techniques, such as the rotating disc electrode, to correlate the catalyst composition with electrochemical performance and durability. With this work, we hope to gain an understanding of composition-structure relationships to enhance the performance of iron-based platinum-free catalysts for PEFCs. Acknowledgements SH2IPDRIVE has received funding from the Ministry of Economic Affairs and Climate Policy, RDM regulation, carried out by the Netherlands Enterprise Agency. References W.F. Lamb et al., 2021, Environmental Research Letters vol. 16.S.T. Thompson et al., 2018, Solid State Ion 319, 68–76.D.A. Cullen et al., 2021, Nature Energy vol. 6 462–474.S.I. Choi et al., 2013, Nano letters 13(7), 3420-3425.P.R. Kumar et al., 2018, Surfaces and Interfaces 12,116-123.D. Schonvogel et al., 2017, Journal of the Electrochemical Society 164(9), F995.A. Mehmood et al., 2022, Nature Catalysis 5(4), 311-323.X. Wan, and J. Shui, 2022, ACS Energy Letters 7(5), 1696-1705.J.C.Tan et al, 2010, Proceedings of the National Academy of Sciences 107(22), 9938-9943.X. Wu et al., 2022, Journal of The Electrochemical Society 169.1, 016507.N.D. Leonard et al., 2018, ACS Catalysis 8(3), 1640-1647.

Carbon Monoxide-Resistant Anode Catalysts for Single-Cell Direct Carbon Monoxide Fuel Cells: Binary, Ternary, And Quaternary Platinum Alloys as Anode Electrocatalysts

The objective of this paper is to present the results of experimentations on the custom-made anode electrocatalysts for direct carbon monoxide fuel cells (DCMFCs) inspired by catalysts commonly used for direct alcohol fuel cells. Seven different catalysts were fabricated and tested. The uniform and consistent manufacturing process and the test procedure allowed a meaningful comparison of the developed fuel cells. The results indicated that homemade Pt-Ru membrane-electrode assembly (MEA) could not compete with the Pt-Sn MEA. While the performance of the MEAs with Pt-Ru-Ni, Pt-Ru-Sn-Ni, and Pt-Ru-Sn-Co was not satisfactory, the Pt-Ru-Sn-Co-W MEA achieved the best performance among all MEAs with Nafion® 117 membrane. The last MEA was made of the Pt-Sn anode catalyst and Nafion® 212 membrane and outperformed all other MEAs by a wide margin. The experiments demonstrated that the performance of the best-developed MEA was three times better than the performance of the commercial Pt-Ru MEA. This means the performance of DCMFCs can be significantly improved by developing a suitable anode electrocatalyst, using a thinner membrane, and operating at optimum conditions. These results are not only applicable for DCMFCs but also are very useful for other proton exchange membrane fuel cells (PEMFCs) operating with CO-containing fuels.

Defect-Engineered Charge Transfer in a PtCu/PrxCe1-xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions.

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO2 nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (Vo) defects were engineered by Pr doping. Besides the Vo monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The Vo concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/PrxCe1-xO2 toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr0.15Ce0.85O2 exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr0.15Ce0.85O2 reached 1.05 and 0.12 A·mg-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant Vo afforded surplus electrons, which tailored the electron transfer between PtCu and PrxCe1-xO2, leading to enhanced catalytic performance of PtCu/PrxCe1-xO2. DFT calculations on PtCu/Pr0.15Ce0.85O2 revealed that Pr doping reduced the band gap of CeO2 and lowered the overpotential.

Production of Metallic Alloy Nanowires and Particles Templated Using Tomato Mosaic Virus (ToMV).

We demonstrate a simple, low-energy method whereby tomato mosaic virus (ToMV) particles can be used to template the production of nanowires and particles consisting of alloys of gold (Au), platinum (Pt) and palladium (Pd) in various combinations. Selective nanowire growth within the inner channel of the particles was achieved using the polymeric capping agent polyvinylpyrrolidone (PVPK30) and the reducing agent ascorbic acid. The reaction conditions also resulted in the deposition of alloy nanoparticles on the external surface of the rods in addition to the nanowire structures within the internal cavity. The resulting materials were characterized using a variety of electron microscopic and spectroscopic techniques, which revealed both the structural and chemical composition of the alloys within the nanomaterials.

Atomically Dispersed Transition Metal-Nitrogen-Carbon Electrocatalysts: Design, Synthesis, Characterization, Reactivity and Durability

Platinum group metal-free (PGM-free) catalysts have been targeted as possible Earth Abundant Elements solution to many electrochemical energy conversion technologies. Special attention has been given to PGM-free electrocatalysis with atomically dispersed (AD) transition metal moieties decorated over nitrogen-doped carbonaceous materials (a.k.a. M-N-C catalysts). Major applications for M-N-Cs are in cathode catalysts for oxygen reduction reaction (ORR). 1 These materials are employed across the pH-range: in proton exchange membrane fuel cells (PEMFC), biological (microbial) fuel cells (MFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). We have successfully introduced M-N-C catalysts synthesized by sacrificial support method (SSM) as a hard template approach based on high temperature pyrolysis.2 In most cases a secondary pyrolysis is being performed to promote AD display of the transition metal.3 This talk will address structure-to-property correlations for M-N-C catalysts in ORR based on electrochemical activity obtained in rotating ring-disk electrodes (RRDE) with those spectroscopic and microscopic observations and density functional theory (DFT) calculations of oxygen binding on AD transition metal. We will discuss the role of the AD transition metal, participation of the surface N-groups as co-catalysts/alternative active sites and the possible role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor. M-N-C catalysts performance in single membrane electrode assembly (MEA) fuel cells will also be discussed in the context of its surface chemistry and materials structure/morphology. We will focus on local hydrophobicity of SSM-based M-N-C electrocatalystsand its impact on the MEA performance.A broad spectrum of AD transition metal decorated MNCs have been synthesized and evaluated for catalytic activity in ORR (and other processes). The use of such materials as “active supports” for highly dispersed platinum or platinum alloy nanoparticles will be discussed. New developments in synthesis protocols enabling “green chemistry” scalable solutions will be discussed.

Thermodynamics and kinetics hydrogen isotope effects of hydrogen/deuterium absorption in Pd-5wt.%Pt alloy

Palladium–Platinum (Pd–Pt) alloys have excellent hydrogen isotope separation properties near room temperature compared to pure palladium (Pd), and are expected to be used as filling materials in thermal cyclic absorption (TCAP) columns. However, most studies on the thermodynamic and kinetic hydrogen isotope effects of hydrogen absorption/deuterium in Pd–Pt alloys have been conducted at temperatures of 273 K or above, with few studies involving the performance of TCAP in the cold-cycle operating temperature range (253 K–303 K). In this work, the performance of Pd-5wt.%Pt alloy for the absorption of hydrogen/deuterium at low temperatures (263 K–323 K) was investigated. The results show that the enthalpy and entropy of dissolution of hydrogen and deuterium in the α-phase of Pd-5wt.%Pt alloy are −11.77 kJ/mol (H), 104.00 J mol−1 K−1(H); −5.50 kJ/mol (D), 87.88 J mol−1 K−1 (D), respectively, which are lower than the enthalpy and entropy change values of pure Pd materials. The apparent reaction activation energies of protium and deuterium absorption are −4.14 kJ/mol (H2) and −11.87 kJ/mol (D2), respectively, which are lower than those of pure palladium. The excellent hydrogen isotope separation performance of Pd–Pt alloys may originate from the fast hydrogen absorption and discharge isotope kinetic performance.

Additive Manufacturing of Platinum Alloys

Additive manufacturing of jewellery alloys has been actively investigated for the past 10 years. Limited studies have been conducted on gold and platinum jewellery alloys. Platinum is of increased interest due to the technological challenges in investment casting. In the present paper, typical platinum jewellery alloys have been tested by laser track experiments on sheet materials. The effect of alloy composition on width and depth of the laser tracks was studied by metallography. Optimum parameters of the laser powder bed fusion (PBF-LB) process were determined for a typical 950Pt jewellery alloy by the preparation of dedicated test samples. Densities of >99.8% were reached for a wide range of processing parameters. However, for real jewellery parts the resulting density was found to depend significantly on the part geometry and on the chosen support structure. The supports must take into account the geometrical orientation of the part relative to the laser build direction and the orientation on the build plate. Local overheating gives rise to porosity in these areas. Therefore, the supports play an important role in thermal management and must be optimised for each part. The design of suitable supports was successfully demonstrated for a typical jewellery ring sample.

Antimicrobial Efficacy of Various Nanoparticles on Addition to Orthodontic Materials- A Systematic Review and Meta-Analysis

Aim: The purpose of this study is to examine the evidence for the efficiency of nanoparticles (NPs) incorporated into orthodontic materials (brackets, bonding agents, wires, acrylic resin, and elastics) in order to enhance their antimicrobial properties. Materials and Methods: A comprehensive search strategy was conducted in electronic databases like PubMed, Cochrane, and Google scholar, books, grey literature like unpublished literature, dissertations, conference reports, etc. Finally, out of all the literature reviewed, a total of 30 articles met the inclusion criteria and were included in the qualitative analysis. For the quantitative analysis, a total of 6 articles were used. Results: Antimicrobial agents such as silver nanoparticles, Titanium dioxide, Silver platinum alloy, zinc oxide and copper oxide, quaternary ammonium dimethacrylate (QADM), Hydroxyapatite crystals, and silver, quaternary ammonium polyethyleneimine (QPEI) particles, silica, and titanium have been incorporated in various orthodontic materials. The incorporation of these nanoparticles into orthodontic materials led to a significant increase in the antibacterial capacity when compared to controls used in the various studies. Conclusion: It can be concluded that the incorporation of nanoparticles into orthodontic materials improves their antibacterial properties. Due to the heterogeneity observed across the studies reviewed, further research with standardized study protocols in terms of the size, concentration, and techniques of incorporation of different NPs into various orthodontic materials is pertinent.

High Performance Air Breathing Zinc-Air Battery with Pt−Ni and Pt−Co Bifunctional Electrocatalyst on N Activated Mesoporous Carbon

In future perspective, the world demands energy conversion and storage devices with high efficiency, lower cost, reliability and sustainability. Zinc air battery (ZAB) has proven capable as metal anodes for producing such energy, as they are Earth-abundant economical, and environmentally resilient, suitable for efficient domestic and industrial applications. Herein, we developed a catalyst, which serves as an excellent bi-functional cathode catalyst for ZAB. Platinum alloy with the transition metals (nickel and cobalt) supported on the nitrogen doped bio derived high mesoporous carbon using a facile method. This catalyst shows the remarkable performance on both the oxygen reduction reaction and oxygen evolution reaction. Platinum alloy (Pt-Ni and Pt-Co) supported on N-activated bio derived mesoporous carbon (N-MC) shows low over potential and high half wave potential over the commercial catalyst in the oxygen reduction reaction. While performance analysis in in-house designed air breathing ZAB, the outstanding performances are achieved with the specific capacity of 746 mAh g−1 for Pt-Co/N-MC and 726 mAh g−1 for Pt-Ni/N-MC, which surpass the commercial Pt-Ru/C catalyst which shows a specific capacity of 420 mAh g−1. The admirable cycling stability over 110 cycles were observed for Pt-Co/N-MC. Undoubtedly, Pt-Co/N-MC and Pt-Ni/N-MC are promising candidates for bi-functional air cathode catalyst for air breathing zinc air battery.

Effects of H2/O2 and H2/O3 gases on PtMo/C cathode PEMFCs performance operating at different temperatures

This study reported the activity of catalysts synthesized from platinum and molybdenum alloys in different atomic ratios and used as cathode electrocatalysts in the PEMFC. The structural properties of PtMo/C and Pt/C catalysts were analyzed by XRD analysis. The composition and distribution of these alloys in Vulcan XC-72R Carbon were determined by SEM and EDX techniques. CV studies assessed electrochemical properties such as ORR and ECSA activity. The performance of PEMFC cathodes that supplied pure hydrogen and oxygen was examined using polarization curves at different temperatures. Another way to improve the cathodic reaction is to use ozone as a potent oxidizing agent. It was measured that the OCV of the H2/O3 PEM fuel cell was 1.60 V, much greater than the open circuit voltage of the traditional H2/O2 PEM fuel cell. The PtMo/C catalyst achieved its highest power density of 137 mWcm−2 at 70 °C, 128 mWcm−2 at 60 °C, 101 mWcm−2 at 50 °C, and 85 mWcm−2 at 40 °C when exposed to H2/O2. As the temperature of the cell was raised, it was seen that the catalyst's catalytic activity increased.The maximum power density was detected to be inversely related to the rise in temperature when ozone was used. At low current densities, however, ozone was observed to greatly boost activation polarization.

Catalytic Etching and Oxidation of Platinum Group Metals: Morphology, Chemical Composition and Structure of Pt, Pd and Rh Foils in the O2 Atmosphere and during NH3 Oxidation with Air at 1133 K

Platinum alloy gauzes are employed for the high-temperature oxidation of NH3 to NO used in the industrial production of HNO3 for application in agricultural fertilizers. To enhance the efficiency of NH3 oxidation, various Pt–Pd–Rh alloys are employed for the production of such catalytic gauzes. To understand the role of these metals in NH3 oxidation, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction were applied to investigate the morphology, composition and structure of Pt, Pd and Rh foils after annealing in O2 and oxidation of NH3 with air at 1133 K. After annealing in O2 and NH3 oxidation, the metallic microgranular structure was detected on Pt(poly), whereas oxide layers of Rh2O3 and PdO were observed on Rh(poly) and Pd(poly). At the onset of NH3 oxidation (t = 1 h), fibrous metal-oxide agglomerates of nanofibers formed on these oxide layers. The long-term (5–10 h) oxidation of NH3 led to the formation of a continuous layer of pyramidal crystals on Rh(poly) and palladium “cauliflowers” on Pd(poly). The highly exothermic reaction of NH3 with oxygen on metals and PdO or Rh2O3 initiates strong catalytic etching forming grains and facets on Pt, fibrous metal-oxide agglomerates, pyramidal crystals and metallic “cauliflowers” on Rh and Pd.

Influence of Thickness of Opaque Porcelain and Alloy Color on the Final Color of Porcelain-Fused-to-Metal Restorations.

Despite the advent of metal-free solutions, porcelain-fused-to-metal restorations (PFM) are still widely used. Particularly for the latest ceramic systems, scarce information is present in the scientific literature about the ideal opaque layer thickness and the alloy color impact to achieve the desired final color of PFM restorations. This study aimed to evaluate the influence of opaque thickness variation layered on different metal alloys on the final color of PFM restorations. Opaque porcelain of one metal−ceramic system (VITA VM13) was layered in four different thicknesses (0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm) on three differently colored dental alloys: a gold−platinum alloy (yellowish), a gold−palladium alloy (light grayish), and a nickel−chromium alloy (dark grayish). The veneering porcelain layered over the opaque was kept constant (Base Dentine 0.45 mm, Transpa Dentine 0.50 mm, and Enamel 0.20 mm). Sixty specimens were fabricated, five samples for each combination of alloy/opaque thickness. The color difference (ΔE) between specimen and reference was measured using a clinical spectrophotometer. The two-way ANOVA revealed that the thickness of both the opaque (p < 0.001) and the metal alloy (p < 0.001) significantly influenced the ΔE values. Gray-colored alloys covered by a 0.10 mm thick opaque layer enabled the closest color match, whereas this occurred for yellow-color alloys covered by a 0.15 mm thick opaque layer. In contrast, the samples covered by a 0.25 mm thick opaque layer obtained the worst ΔE.

Alternative and facile production pathway towards obtaining high surface area PtCo/C intermetallic catalysts for improved PEM fuel cell performance.

The design of catalysts with stable and finely dispersed platinum or platinum alloy nanoparticles on the carbon support is key in controlling the performance of proton exchange membrane (PEM) fuel cells. In the present work, an intermetallic PtCo/C catalyst is synthesized via double-passivation galvanic displacement. TEM and XRD confirm a significantly narrowed particle size distribution for the catalyst particles compared to commercial benchmark catalysts (Umicore PtCo/C). Only about 10% of the mass fraction of PtCo particles show a diameter larger than 8 nm, whereas this is up to or even more than 35% for the reference systems. This directly results in a considerable increase in electrochemically active surface area (96 m2 g-1 vs. >70 m2 g-1), which confirms the more efficient usage of precious catalyst metal in the novel catalyst. Single-cell tests validate this finding by improved PEM fuel cell performance. Reducing the cathode catalyst loading from 0.4 mg cm-2 to 0.25 mg cm-2 resulted in a power density drop at an application-relevant 0.7 V of only 4% for the novel catalyst, compared to the 10% and 20% for the commercial benchmarks reference catalysts.

Methodical designing of Pt3−xCo0.5+yNi0.5+y/C (x = 0, 1, 2; y = 0, 0.5, 1) particles using a single-step solid state chemistry method as efficient cathode catalyst in H2-O2 fuel cells

A cathode catalyst possessing increased activity for oxygen reduction reaction (ORR) with superior durability is greatly required for polymer electrolyte membrane fuel cells (PEMFCs). Although Platinum (Pt) alloys have been widely studied for ORR, their real time application in fuel cells still remains a challenging task. Chemically ordered Pt alloys have attracted widespread attention due to the unique electronic and geometric factors that boost their electrocatalytic activity. Therefore, it is highly urgent to fabricate such ordered alloys as efficient cathode catalysts in fuel cells. Herein we report for the first time, a one-step solid-state method for the preparation of Pt3−xCo0.5+yNi0.5+y/C (x = 0, 1, 2; y = 0, 0.5, 1) nanoparticles on carbon support. Different compositions of this catalyst were studied and Pt2Co1Ni1/C was found to be the optimal, best performing catalyst both under half-cell and full-cell conditions. Interestingly, the mass activity of Pt2Co1Ni1/C was found to be seven times higher than that of commercial Pt/C in an acidic medium, achieving the Department of Energy (DOE) target for 2025. Moreover, a retention in mass activity after 50k cycles confirmed the superiority of this catalyst in effectively catalysing ORR reactions under an acidic medium. Importantly, the peak power density achieved by Pt2Co1Ni1/C under actual PEMFC operating conditions outperforms the commercially used Pt/C. Thus, this work provides a new approach for the simple and scalable synthesis of optimal cathode catalysts for fuel cells, opening up new dimensions in the field of energy research.

Trimetallic Nanostructures of Silver–Platinum Alloy Shells on Gold Nanorods for Plasmon-Mediated Photocatalysis

Trimetallic Nanostructures of Silver–Platinum Alloy Shells on Gold Nanorods for Plasmon-Mediated Photocatalysis

Electronic Perturbation of Platinum Alloy By Transition Metal-Doping Towards Improved ORR Activity and Stability

As of today, Pt-based catalysts are the predominant ORR catalysts that meet the desired activity requirements of ORR in fuel cells. However, their broader applications are still challenging due to highly sluggish ORR kinetics, limited stability and higher cost of Pt. In order to develop novel electrocatalyst materials, herein we report surface tuning of binary PtCo alloy through transition metal doping, which reveals superior ORR activity achieving a mass activity of 2.07 A mgPt -1 at 0.9 V vs. reversible hydrogen electrode (RHE) and excellent durability with minor degradation after 30000 cycles. The ternary PtCoMn@NGNS alloy prepared through facile molten salt pyrolysis reveals a strong metal-support interaction via metal-nitrogen-graphene coordination.Furthermore, Mn dopants alter the electronic structure of Pt alloy, which improves the oxygen-intermediate binding energy on the interface and suppress the Co dissolution through unique configuration, resulting in enhanced activity and durability of the catalyst. According to the DFT calculations, the surface Mn extensively adsorbs an OH, resulting in increased surface Co stability and overall ORR catalytic performance. Therefore, it is understandable that the development of ternary Pt alloy results in considerable changes in the structural and electrical characteristics of metal overlayer, which varies dramatically from monometallic surfaces.Our experimental results corroborated by theoretical calculations show that electronic perturbation of PtCo by Mn doping stabilizes the Co and causes significant strain in the Pt(111), which accounts for the increased ORR performance. The strained lattice of Pt caused by Co alloying and surface segregation of Mn both play important roles in the increased ORR activity. Similarly, the Pt3CoMn-OH configuration diminishes Co dissolution and improves overall stability. It is anticipated that such a facile preparation of high-performance electrocatalysts will advance the practical applications of ORR catalysts.Figure 1: Figure 1

Mitigation of Performance Degradation of Cathodes for Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are green energy conversion devices that convert chemical energy to electrical energy. Compared to other types of fuel cells, PEMFCs have various advantages including the low operating temperature, high power density, and short start-up times [1, 2]. However, the limited durability and high cost of platinum catalysts are the primary obstacles to the large scale commercialization of PEMFCs. Hence, a variety of scientific approaches have tried to improve the durability of Pt electrocatalysts as a main component of PEMFC membrane electrode assemblies (MEAs) [3]. Studies reported that the performance degradation of the catalyst layer in MEAs can be divided into the reversible and irreversible degradation processes. The first case is the permanent degradations caused by the platinum dissolution or corrosion of carbon support. It is well known results in PMEFC MEAs that carbon corrosion mainly occurs at operating conditions of higher than 1.0 V, whereas platinum agglomeration/dissolution happen at 0.6‒1.0 V. That is, the deterioration of platinum in the cathode is unavoidable under general PEMFC operating conditions of 0.6‒1.0 V [4, 5]. Numerous studies, such as tuning of platinum alloy composition and use of highly durable Pt-alloy catalysts have been conducted to suppress irreversible performance degradation [6-8]. In the reversible degradation phenomena, oxygen or hydroxyl groups are bonded to platinum in the cathode, which interferes with oxygen reduction reactions and reduces performance. However, even reversible degradation can result in permanent performance decay if not removed for a long time. Hence, researches on the strategies to mitigate reversible degradation are necessary to extend the lifetime of PEMFC MEAs. In particular, Pt-O film generated during operation is reversible and can be easily recovered by the periodical reduction of cathode potential [9, 10]. In this research, we develop the mitigation method to prevent performance degradation of MEAs during constant current operation. In addition, we quantitatively analyze the mitigation mechanism of MEAs via various physicochemical and electrochemical analysis tools.

Enhanced ammonia sensitivity electrochemical sensors based on PtCu alloy nanoparticles in-situ synthesized on carbon cloth electrode

The alloying of Pt with transition metals is significant in boosting the performance of Pt-based electrochemical sensors. In this paper, Platinum and copper alloy nanoparticles (PtCu NPs) were in-situ loaded on carbon cloth (CC) by electrochemical deposition to obtain a self-supported electrode (PtCu-CC) for electrochemical detection of ammonia. The alloying of Pt and Cu reduced the crystal lattice spacing of Pt and improved the catalytic performance of ammonia. Therefore, the PtCu-CC electrode displayed visibly enhanced ammonia detection performance compared with the Pt-CC electrode and commercial Pt electrode. The linear range for ammonia determination was from 0.5 to 40 and 40–500 μM, and the sensitivity of the Pt7Cu1-CC sensor was 9.5 μA μM−1 cm−2 and 0.778 mA lg μM−1 cm−2, respectively. The detection limit was 8.6 ± 0.32 nM, and the quantification limit was 28.67 ± 0.73 nM. The developed sensor shows good anti-interference capability, reproducibility and stability; in addition, it exhibited good capacity in the actual water sample test. PtCu alloy nanoparticles were applied to ammonia detection in water, which may broaden the ways of ammonia detection in water.

MICROSCOPE. mission analysis, requirements and expected performance

The MICROSCOPE mission aimed to test the weak equivalence principle (WEP) to a precision of 10−15. The WEP states that two bodies fall at the same rate on a gravitational field independently of their mass or composition. In MICROSCOPE, two masses of different compositions (titanium and platinum alloys) are placed on a quasi-circular trajectory around the Earth. They are the test-masses of a double accelerometer. The measurement of their accelerations is used to extract a potential WEP violation that would occur at a frequency defined by the motion and attitude of the satellite around the Earth. This paper details the major drivers of the mission leading to the specification of the major subsystems (satellite, ground segment, instrument, orbit…). Building upon the measurement equation, we derive the objective of the test in statistical and systematic error allocation and provide the mission’s expected error budget.

Result of the MICROSCOPE weak equivalence principle test

The space mission MICROSCOPE dedicated to the test of the equivalence principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations (a A and a B) of two test masses in terms of the Eötvös parameter . No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 h down to the limit of the statistical error which is smaller than 10−14 for η(Ti, Pt). Accumulating data from all segments leads to η(Ti, Pt) = [−1.5 ± 2.3 (stat) ± 1.5 (syst)] × 10−15 showing no EP violation at the level of 2.7 × 10−15 if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the Eöt-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null Eötvös parameter with a statistical uncertainty of 1.1 × 10−15.