XAFS Techniques Research Articles

Atomically dispersed bimetallic FeZn-N-C with oxidase-like performance: Synthesis, characterization, calculation and activity

The burgeoning interest in single atom catalysts (SACs) stems from their exceptional oxidase-mimicking capabilities, driving substantial advancements in this field. Nevertheless, a critical knowledge gap remains regarding the influence of Zn incorporation on the oxidase-like activity of atomically dispersed Fe-N-C catalysts. This study successfully synthesized and comprehensively characterized three distinct SACs (FeZn SAC-N@C, Fe SAC-N@C, and Zn SAC-N@C) using TEM, HAADF-STEM, XRD, XPS, BET, ICP-MS, and XAFS techniques. Activity assays revealed that FeZn SAC-N@C exhibited the highest oxidase-mimicking activity, with Fe SAC-N@C displaying moderate activity, whereas Zn SAC-N@C did not exhibit oxidase-like behavior. The superior oxidase-like activity of FeZn SAC-N@C is attributed to its enhanced O2 activation capacity, characterized by a high free energy of 0.90 eV in the rate-determining reaction step, surpassing those of Fe SAC-N@C (0.85 eV) and Zn SAC-N@C (0.71 eV). EPR and DFT calculations elucidated the catalytic mechanism of FeZn SAC-N@C, involving the generation of O2− radicals. As a proof-of-concept, FeZn SAC-N@C demonstrates potential as a colorimetric sensor for detecting ascorbic acid and nitrite, achieving a limit of detection of 0.77 μM for ascorbic acid and 0.16 μM for nitrite. These findings open a new avenue for configuring bimetallic atomically dispersed catalysts with oxidase-like activity in future research.

Universal Intercalation/Alloying Hybrid Mechanism with -ICOHP Criterion in MAX Toward Steadily Ascending Lithium-Ion Batteries.

Profiting from the unique atomic laminated structure, metallic conductivity, and superior mechanical properties, transition metal carbides and nitrides named MAX phases have shown great potential as anodes in lithium-ion batteries. However, the complexity of MAX configurations poses a challenge. To accelerate such application, a minus integrated crystal orbital Hamilton populations descriptor is innovatively proposed to rapidly evaluate the lithium storage potential of various MAX, along with density functional theory computations. It confirms that surface A-element atoms bound to lithium ions have odds of escaping from MAX. Interestingly, the activated A-element atoms enhance the reversible uptake of lithium ions by MAX anodes through an efficient alloying reaction. As an experimental verification, the charge compensation and SnxLiy phase evolution of designed Zr2SnC MAX with optimized structure is visualized via in situ synchrotron radiation XRD and XAFS technique, which further clarifies the theoretically expected intercalation/alloying hybrid storage mechanism. Notably, Zr2SnC electrodes achieve remarkably 219.8% negative capacity attenuation over 3200 cycles at 1Ag-1. In principle, this work provides a reference for the design and development of advanced MAX electrodes, which is essential to explore diversified applications of the MAX family in specific energy fields.

Synthesis, crystal structure, and thermal behavior of Pt-based heterometallics [PtPy4](FcCOO)2 and trans-[PtPy2(FcCOO)2

Novel square-planar Pt-based heterometallic complexes with ferrocenecarboxylic acid were prepared in two steps from (tetrapyridine)platinum diacetate [PtPy4](OAc)2. The crystal structure of [PtPy4](FcCOO)2 and [PtPy2(FcCOO)2] was established by single crystal X-ray diffraction. Subsequent thermal transformation of a trinuclear compound [PtPy2(FcCOO)2] to a bimetallic Pt–Fe phase was studied by XAFS techniques.

Electronic Structure Study of Ni-B Alloy Coatings by XAFS Technique

Electronic Structure Study of Ni-B Alloy Coatings by XAFS Technique

One-pot production of dioctyl ether from 1,2-octanediol over rutile-titania-supported palladium-tungsten catalyst

Direct synthesis of dioctyl ether by catalytic reduction of 1,2-octanediol (1,2-OcD) was investigated with various supported catalysts containing W and noble metals. The combination of rutile TiO2 support and Pd with W showed the highest yield of dioctyl ether, up to ca. 45 % (carbon-based). The catalytic activity much depended on the W loading amount, and the amount corresponded to monolayer coverage or more was necessary to obtain good yield. The data at low conversion levels showed that the reaction started with WOx/TiO2-catalyzed dehydration of 1,2-OcD to octanal, which then reacted with 1,2-OcD to give acetal. The stepwise hydrogenolysis of the acetal gave dioctyl ether. The WOx-Pd/TiO2 was significantly deactivated during uses, and the deactivated catalyst even lost the activity in 1,2-OcD dehydration. The characterization results of the used catalyst were not much different from the fresh one with XRD, Raman, NH3-TPD, IR of adsorbed pyridine and XAFS techniques. Metastable minor site on WOx/TiO2 was probably responsible to the catalytic activity.

Local structural changes in Ce1-xLnxO2-δ (Ln = La, Gd) solid electrolytes

The local structural changes in La and Gd in doped ceria were investigated using the XAFS technique. In addition, Ce1-xLnxO2-δ (Ln = La, Gd; LDC) (0 ≤ x ≤ 0.5) was synthesized through a coprecipitation method and the local structures were analyzed based on the XAFS spectra for the first and second neighbor shells of the constituent cations. For these two types of materials, the variation in the coordination number of the Ln and Ce cations showed different trends as a function of the dopant concentration, x. For LDC, a local structural ordering was formed at x ≥ 0.3 similar to a pyrochlore-type structure, in which the oxygen vacancies are preferentially located adjacent to La3+. For Ce1-xGdxO2-δ (GDC), no distinct differences in the coordination number of the cations were observed.The combined XAFS and XRD results successfully showed that the weighted average distances of the longer Ln-Ln (Ln = La for LDC and Ln = Gd for GDC) and shorter Ce-Ce at each composition, as obtained through XAFS analysis, fit extremely well with the lattice parameter obtained using XRD. A model of the local structural change was derived to explain the variation in the electrical conductivity during the early stage of Ln doping.

Characterization of ARDESIA: a 4-channel SDD X-ray spectrometer for synchrotron measurements at high count rates

ARDESIA is an SDD-based, X-ray spectrometer, optimized for synchrotron measurements that require high count rates (>1 Mcounts/s/channel) and good energy resolution (<130 eV of FHWM Mn-Kα line at optimum shaping time, ⩽ 200 eV at short shaping times). The main target applications are XRF and XAFS techniques. The detection module consists of 2×2 pixel monolithic SDD (5 mm pitch) coupled with a 4-channel version of the CUBE CMOS preamplifier. The mechanical structure of the instrument has been realized to fit inside a sample chamber with a finger-like structure. The system grants proper cooling (-40oC) and operation in vacuum. ARDESIA is also equipped with two auxiliary electronic boards: one for SDD powering and biasing and the other for closed-loop driving of two Peltier TECs. The output signals of the instrument are processed by digital pulse processors using short pulse processing times in order to achieve good spectroscopic performance at high count rates. Two different measurement campaigns were performed at synchrotron beamlines to assess the performance of the instrument. At the LNF DAΦNE-Light DXR1 soft X-ray beamline, XRF measurements on low atomic number elements (down to C-K line, 277 eV) demonstrated the good energy resolution of the spectrometer and made possible to acquire the first XAFS spectrum of Silicon K-edge in a PyrexTM glass sample. At the LISA CRG beamline at ESRF—Grenoble, XAFS measurements on different samples, such as kesterite and protochabourn'eite, were performed, demonstrating the high count rate capability and stability of the instrument over time.

ARDESIA: A fast silicon drift detector X‐ray spectrometer for synchrotron applications

ARDESIA, a four‐channel X‐ray spectrometer based on silicon drift detectors (SDDs), is presented. It has been developed for synchrotron applications targeting especially X‐ray fluorescence (XRF) and X‐ray absorption spectroscopy (XAS) with good energy resolution at high count rates (a few Mcps per second). The main target applications are XRF and XAFS techniques. The system features a 2 × 2 monolithic array of 5‐mm‐pitch SDDs cooled with a double Peltier scheme and coupled to a four‐channel CUBE charge preamplifier. Different digital pulse processors allowing operation in Mcps per second count rates are employed. The results of preliminary characterization measurements performed at both the LNF DAΦNE‐Light DXR1 beamline and the ESRF LISA BM‐08 are reported, in particular, XRF measurements on low atomic number elements (down to the Carbon K‐line, 270 eV) and extended X‐ray absorption fine structure of trace materials in pyrite.

Identifying the single active site in MoS2-based hydrogen evolution electrocatalyst by XAFS technique

The strong metal-support interactions endow the single-atom catalysts outstanding behavior in water splitting. However, accurately characterizing the coordination and electronic structure of the active sites is still a challenge. Here, we report the synthesis of atomically dispersed Co sites anchored on the MoS2 nanosheet and discover its superior performance in the hydrogen evolution reaction (HER). The X-ray absorption spectra at both Co K-edge and L-edge reveals the coordination environment and valence state of the Co single atom, and density functional theory calculations confirm that the active sites are S atoms bonding with Co single atoms. This study suggests the promising potential of Co1/MoS2 as a hydrogen evolution electrocatalyst.

Phase-separated magnetic ground state in Mn3Ga0.45Sn0.55C

Existence of non-ergodic ground states is considered as a precursor to a first order long range magnetostructural transformation. Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C lies compositionally between two compounds, Mn$_3$GaC and Mn$_3$SnC, undergoing first order magnetic transformation. Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C though crystallizes in single phase cubic structure, exhibits more than one long range magnetic transitions. Using a combination of magnetization, ac susceptibility, neutron diffraction and XAFS techniques it is shown that, though Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C exhibits long range magnetic order, it presents a cluster glassy ground state due to formation of magnetically ordered Ga rich and Sn rich clusters. The clusters are big enough to present signatures of long range magnetic order but are distributed in such way that it limits interactions between two clusters of the same type leading to a frozen magnetic state at low temperatures. The main reason for such a cluster glass state is the difference in local structure of Mn atoms that find themselves in Ga rich and Sn rich clusters.

放射光XAFSおよびイメージングXAFS法による模擬ガラス試料中のロジウム元素の化学状態分析

放射光XAFSおよびイメージングXAFS法による模擬ガラス試料中のロジウム元素の化学状態分析

Immobilization of As(V) in Rhizopus oryzae Investigated by Batch and XAFS Techniques.

Arsenic (As) contamination in aqueous solutions has become an increasing public concern due to the immense harm to human health. Herein, bioaccumulation of arsenate (As(V)) by Rhizopus oryzae in aqueous systems was investigated under different environmental conditions, such as different pH’s, ionic strengths, mycelia dosages, mycelia growths, and temperatures. The results showed that As(V) could be bioaccumulated efficiently by R. oryzae, and the maximum bioaccumulation capacity of As(V) in R. oryzae was 52.4 mg/g at T = 299 K, which was much higher than that for other biomaterials under similar conditions. R. oryzae generated a higher content of thiol compounds under As(V) stress to immobilize As(V) from aqueous solutions. X-ray absorption near-edge spectroscopy analysis indicated that As(V) was partly reduced to As(III) with increasing contact time, which increased As(V) bioaccumulation in mycelia. In addition, extended X-ray absorption fine structure analysis showed that the As–S complex played an important role in As(V) immobilization by mycelia. This study provided an in-depth investigation of intracellular As speciation and coordination in R. oryzae on the molecular scale, which was crucial to understand the interaction mechanisms of As(V) with fungi during environmental cleanup.

Development of Highly Active and Durable Pt-Pd System Catalysts for PEFCs

Introduction Carbon supported Pd core-Pt shell catalyst (Pt/Pd/C) and Pt-Pd alloy catalyst (PtPd/C) are attractive alternatives to a carbon supported Pt catalyst (Pt/C) because their ORR specific activities are enhanced with an accelerated durability test (ADT) performed at 80°C [1, 2]. However, ECSA of the catalysts drastically decreased with the ADT, resulting in slight increase of ORR mass activities. We explored the ADT protocol and developed a high activation protocol (HAP) to mitigate the ECSA decay and enhance the ORR mass activities. Furthermore, we developed a Cu-O2 treatment which mimics the HAP carried out on GC electrode and is suitable for mass-production of highly activated catalysts. We also applied SiO2 coating technique [3, 4] to prevent agglomeration of the catalyst particles with the ADT and improve durability of the catalysts. Experimental Pt/Pd/C was synthesized with a modified Cu-UPD/Pt replacement process [1]. A carbon supported Pd core (Pd/C, Pd size: 4.6 nm, Pd loading: 30 wt.%, Ishifuku Metal Industry) was dispersed in 50 mM H2SO4 containing 10 mM CuSO4 and the solution was stirred with co-existence of a metallic Cu sheet at 5°C under Ar atmosphere. After stirring for 5 h, the Cu sheet was removed and K2PtCl4 was added to replace under potentially deposited Cu shell on the Pd core surface with Pt shell. PtPd/C alloy catalyst was synthesized with an impregnation method. Pt(acac)2 and Pd(acac)2 were impregnated onto a carbon support using t-butylamine as a solvent (Pt20Pd80 in at.%), followed by reduction under 15% H2/Ar atmosphere at 600°C for 4 h. The catalysts were characterized by TG, XRF, XRD, TEM, CV and XAFS techniques. ORR activity of the catalysts was evaluated with RDE technique in O2 saturated 0.1 M HClO4 at 25°C. ADT was conducted using rectangular wave potential cycling of 0.6 V (3 s)-1.0 V (3 s) vs. RHE in Ar saturated 0.1 M HClO4 at 80°C for 10,000 cycles. Results and Discussion Changes in ECSA and ORR mass activity of the Pt/Pd/C and PtPd/C catalysts with ADT, HAP and Cu-O2 treatment are summarized in Fig. 1 (dotted black lines show Pt/C catalyst; Pt size: 2.8 nm, Pt loading: 46 wt.%, TEC10E50E, TKK). The ECSA of the catalysts drastically decreased with the ADT, by which the ORR mass activity showed slight increases. On the contrary, the ECSA decay was mitigated with the HAP (rectangular wave potential cycling of 0.4V (300 s)-1.0 V (300 s) vs. RHE in Ar saturated 0.1 M HClO4 at 80°C for 30-40 cycles) and the ORR mass activity was highly enhanced, showing ca. 3-fold values of the Pt/C catalyst. Since the HAP is performed on the GC electrode, treated amount of the catalysts is extremely small (ca. 30 µg), we developed a Cu-O2 treatment (Fig. 2) to scale-up the HAP. In the Cu-O2 treatment, the catalyst powders are stirred for 300 s in 2 M H2SO4 containing 0.1 M CuSO4 at 80°C under an inert atmosphere (N2) with co-existence of a metallic Cu sheet, where the equilibrium potential of Cu2+/Cu (ca. 0.3 V) is applied to the catalysts when they contact with the Cu sheet. Next, the Cu sheet is removed and O2 gas is introduced in the solution, where the equilibrium potential of the ORR (ca. 1.0 V) is applied to the catalysts. As shown in Fig. 1, the ECSA decay by the Cu-O2 treatment is equivalent to that by the HAP and the ORR mass activity of the catalysts were equivalently enhanced, indicating that the Cu-O2 treatment mimics the HAP on the GC electrode and is suitable for mass-production of highly activated Pt/Pd/C and PtPd/C catalysts. However, the highly activated Pd@Pt NPs were severely agglomerated with the ADT and the ORR mass activity was decayed. In order to prevent the NPs agglomeration with the ADT, we applied SiO2 coating onto the Pd@Pt NPs [3, 4]. The SiO2 coating suppressed the NPs agglomeration and the ECSA decay was mitigated (Fig. 3), which highly enhanced the ORR mass activity of the Pt/Pd/C catalyst even after the ADT (Fig. 4). Acknowledgement This work was supported by NEDO, Japan.

Spatially Non-Uniform Degradation of Pt/C Cathode Catalysts in Polymer Electrolyte Fuel Cells Imaged by Combination of Nano XAFS and STEM-EDS Techniques

This account article treats with spatially non-uniform degradation events of Pt/C cathode catalysts in polymer electrolyte fuel cells involving the formation and dissolution of positively charged Pt ions and detachment of metallic Pt nanoparticles/clusters, which were visualized by the same-view nano XAFS and STEM-EDS imaging technique under humid N2 atmosphere.

Cu3(PO4)2/C composite as a high-capacity cathode material for rechargeable Na-ion batteries

Conversion-type materials are an appealing alternative to conventional intercalation compounds as cathode materials for sodium ion batteries, due to their high capacities. In this paper, we report for the first time that carbon-coated copper phosphate (Cu3(PO4)2/C) can be used as a novel high-capacity cathode for rechargeable Na batteries. Cu3(PO4)2/C shows a reversible capacity up to 290mAhg−1 at a current of 20mAg−1and 190mAhg−1 at 400mAg−1, with capacity retention of 210 and 160mAhg−1 respectively after 30 cycles. The detailed sodium storage mechanisms were studied by employing ex-situ XRD, HR-TEM, solid-state NMR and XAFS techniques. The results clearly indicate that Cu3(PO4)2 can transform into Na3PO4 and Cu particles after discharge. Furthermore, Cu can react with Na3PO4 to form copper phosphate and NaxCuyPO4 in the charge process, determining the rechargeability of Cu3(PO4)2.

XAFS study on structure-activity correlations of α-Co(OH)2 nanosheets water oxidation catalysts

Understanding the structure-activity of the metal hydroxide materials is critical to the design of an efficient oxygen evolution reaction (OER) catalyst for water oxidation. A challenge is to identify and collect surface active site relative to bulk. Here, we have prepared an ultrathin α-Co(OH)2 nanosheet with large exposed surface Co sites as an high-efficiency O2 evolution catalyst. Using XAFS technique, we have investigated the oxidation state and local structural evolutions of the α-Co(OH)2 nanosheets catalyst. A coordination-miss Co sites (CoO6-x) with oxidation state of +3.3 on the nanosheet surface is revealed after the OER procedure, indicating the in situ formation of y-CoOOH nanosheet is a key factor leading to an enhanced water oxidation performance.

Gold nanoparticles on mesoporous Cerium-Tin mixed oxide for aerobic oxidation of benzyl alcohol

In the era of sustainable chemistry the development of nanocatalysis has drawn special attention. Here we report the preparation of nanocrystalline, mesoporous cerium-tin oxide solid solutions and tested for selective oxidation of benzyl alcohol, cinnamyl alcohol, 4-methylbenzyl alcohol, 2-octanol, and geraniol using molecular oxygen as an oxidant. Among different mesoporous supports with Ce/Sn compositions (98/2, 95/5, 90/10 and 80/20, the highest activity was found for the Ce-Sn mixed oxide (Ce/Sn=95/5) supported gold nanoparticles. The microkinetic study shows that there was no mass transfer limitation in three phase catalytic system. The supports and the corresponding gold catalysts were extensively characterized by N2 physisorption, XRD, H2-TPR, NH3-TPD, TEM, XPS, RAMAN and XAFS techniques. The nanocrystalline solid solution of CexSn1-xO2 was detected by XRD analysis. The presence of oxide vacancy was confirmed by XPS and RAMAN studies. The reducibility of Ce-Sn mixed oxide support increased upon gold deposition which was confirmed by H2-TPR techniques. The TPD study indicates the alteration of acid-basic sites of the CeO2 oxide upon incorporation of tin and gold nanoparticles. The cooperative role between the gold species and the ceria-tin support has been observed while correlating the catalytic activity results with the characterization studies.

時間分解 X 線吸収分光法による担持金属触媒の状態変化メカニズムへのアプローチ

時間分解 X 線吸収分光法による担持金属触媒の状態変化メカニズムへのアプローチ

Anionic starch-induced Cu-based composite with flake-like mesostructure for gas-phase propanal efficient removal

Highly crystalline flake-like CuCeO2−δ composites (strCCx) with large specific surface area and developed mesoporosity were prepared using an economic and effective bio-template route. Modified starch with abundant surface carboxyl groups was adopted as the chelating agent and template for metal cations immobilization via electrostatic attraction predominately based on the process of –COO−⋯Cu2+ and –COO−⋯Ce3+. Physicochemical properties of prepared materials were systematically explored by FT-IR, XRD, TG, N2 adsorption/desorption, FE-SEM, TEM, H2-TPR, O2-TPD, XPS, DRUV–Vis, and XAFS techniques. Propanal as a typical oxygen-contained VOC was adopted as the probe pollutant to evaluate the catalytic performance of synthesized materials. Characterization results reveal that plenty of copper ions in composite oxides are incorporated into CeO2 lattice, which produces oxygen vacancies and enhances metal reducibility. Both specific surface area and pore volume of strCCx samples decreased with the increasing of Cu loading. The flake-like CuCeO2−δ sample (Cu/(Cu+Ce)=0.15) with highest specific surface area (108.2m2/g) and surface oxygen concentration is indentified as the most active catalyst with propanal totally destructed at 230°C. The introduction of H2O has a negative effect on propanal removal, and the synthesized catalyst has high tolerance to moisture. In conclusion, the specific surface area and surface oxygen density are two vital factors governing the catalytic activity of composite catalysts.

Synergetic effect of a pillared bentonite support on SE(VI) removal by nanoscale zero valent iron

A positively-charged pillared bentonite (Al-bent) was used as the carrier of nanoscale zerovalent iron (NZVI) particles for accelerating the reductive removal of anionic Se(VI) from water by NZVI. A synergetic effect on Se(VI) removal by this NZVI/Al-bent composite was observed, with removal efficiency (95.7%) much higher than the sum (72.0%) of NZVI reduction (62.1%) and Al-bent adsorption (9.86%). The multiple roles of Al-bent in the reaction system of Se(VI) with NZVI were comprehensively investigated using XAFS techniques, XRD analysis, kinetic studies and pH monitoring. The results indicate that the positively-charged Al-bent as a good adsorbent to anionic Se(VI) accelerated the reductive transformation of Se(VI) into less soluble Se(-II). Al-bent also acted as a pH buffering agent, and contributed to the enhanced stability and reusability of NZVI. In addition, Al-bent could transfer the insoluble reduction products away from the iron surface according to EXAFS studies. Particularly, Al-bent could activate Fe(II) ions generated in the reaction system through an appropriate bonding at pH 8.0, and provide NZVI with an extra reduction capacity. The results indicate the significance of correct matching of bentonite support to target contaminant for developing novel remediation technique based on this natural mineral.