Transient Kinetic QXAFS Approach for Understanding the RDE-MEA Gap in Fuel Cell (Oxygen Reduction Reaction) Performances of Pt-Based Electrocatalysts.

There is a large gap between the performances indicated by rotating disk electrode (RDE) results in acidic media and the actual performances obtained in membrane-electrode assemblies (MEAs) composed of the same electrocatalysts. It is unclear whether the intrinsic kinetic reactivity of the available surface Pt sites of Pt-based cathode electrocatalysts is similar or different at RDE and in MEA. To address this, we used an operando element-selective time-resolved Pt L-edge quick X-ray absorption fine structure (QXAFS) technique to determine transient response profiles and rate constants, , , and , corresponding to changes in the oxidation states [white line (WL) intensity] and local structures (coordination numbers of Pt-O and Pt-Pt bonds) at Pt sites for nine representative Pt-based cathode electrocatalysts under transient voltage operations, aiming to understand the oxygen reduction reaction (ORR) performance gap between RDE and MEA.

Imaging of Ce Radical Scavengers in a Practical Polymer Electrolyte Fuel Cell by 3D Fluorescence CT-XAFS and Depth-Profiling Nano-XAFS-SEM/EDS Techniques.

There is little information on the spatial distribution, migration, and valence of Ce species doped as an efficient radical scavenger in a practical polymer electrolyte fuel cell (PEFC) for commercial fuel cell vehicles (FCVs) closely related to a severe reliability issue for long-term PEFC operation. An three-dimensional fluorescence computed tomography-X-ray absorption fine structure (CT-XAFS) imaging technique and an same-view nano-XAFS-scanning electron microscopy (SEM)/energy-dispersive spectrometry (EDS) combination technique were applied for the first time to perform spatial visualization and depth-profiling analysis of Ce radical scavengers in a practical PEFC of Toyota MIRAI FCV under PEFC operating conditions. Using these techniques, we successfully visualized and analyzed the domain, density, valence, and migration of Ce scavengers that were heterogeneously distributed in the components of PEFC, such as anode microporous layer, anode catalyst layer, polymer electrolyte membrane (PEM), cathode catalyst layer, and cathode microporous layer.

Visualization and understanding of the degradation behaviors of a PEFC Pt/C cathode electrocatalyst using a multi-analysis system combining time-resolved quick XAFS, three-dimensional XAFS-CT, and same-view nano-XAFS/STEM-EDS techniques.

We developed a multi-analysis system that can measure in situ time-resolved quick XAFS (QXAFS) and in situ three-dimensional XAFS-CT spatial imaging in the same area of a cathode electrocatalyst layer in a membrane-electrode assembly (MEA) of a polymer electrolyte fuel cell (PEFC) at the BL36XU beamline of SPring-8. The multi-analysis system also achieves ex situ two-dimensional nano-XAFS/STEM-EDS same-view measurements of a sliced MEA fabricated from a given place in the XAFS-CT imaged area at high spatial resolutions under a water-vapor saturated N atmosphere using a same-view SiN membrane cell. In this study, we applied the combination method of time-resolved QXAFS/3D XAFS-CT/2D nano-XAFS/STEM-EDS for the first time for the visualization analysis of the anode-gas exchange (AGEX) (simulation of the start-up/shut-down of PEFC vehicles) degradation process of a PEFC MEA Pt/C cathode.

Visualization Analysis of Pt and Co Species in Degraded PtCo/C Electrocatalyst Layers of a Polymer Electrolyte Fuel Cell Using a Same-View Nano-XAFS/STEM-EDS Combination Technique.

In order to obtain a suitable design policy for the development of a next-generation polymer electrolyte fuel cell, we performed a visualization analysis of Pt and Co species following aging and degradation processes in membrane-electrode assembly (MEA), using a same-view. Nano-X-ray absorption fine structure (XAFS)/Scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDS) technique that we developed to elucidate durability factors and degradation mechanisms of a MEA PtCo/C cathode electrocatalyst with higher activity and durability than a MEA Pt/C. In the MEA PtCo/C, after 5000 ADT-rec (rectangle accelerated durability test) cycles, unlike the MEA Pt/C, there was no oxidation of Pt.

An Integrated Single-Electrode Method Reveals the Template Roles of Atomic Steps: Disturb Interfacial Water Networks and Thus Affect the Reactivity of Electrocatalysts.

A method enabling the accurate and precise correlation between structures and properties is critical to the development of efficient electrocatalysts. To this end, we developed an integrated single-electrode method (ISM) that intimately couples electrochemical rotating disk electrodes, in situ/operando X-ray absorption fine structures, and aberration-corrected transmission electron microscopy on identical electrodes. This all-in-one method allows for the one-to-one, in situ/operando, and atomic-scale correlation between structures of electrocatalysts with their electrochemical reactivities, distinct from common methods that adopt multisamples separately for electrochemical and physical characterizations.

Key Factors for Simultaneous Improvements of Performance and Durability of Core-Shell Pt Ni/Carbon Electrocatalysts Toward Superior Polymer Electrolyte Fuel Cell.

It remains a big challenge to remarkably improve both oxygen reduction reaction (ORR) activity and long-term durability of Pt-M bimetal electrocatalysts simultaneously in the harsh cathode environment toward widespread commercialization of polymer electrolyte fuel cells (PEFC). In this account we found double-promotional effects of carbon micro coil (CMC) support on ORR performance and durability of octahedral Pt Ni nanoparticles (Oh Pt Ni/CMC). The Oh Pt Ni/CMC displayed remarkable improvements of mass activity (MA; 13.

Observation of Degradation of Pt and Carbon Support in Polymer Electrolyte Fuel Cell Using Combined Nano-X-ray Absorption Fine Structure and Transmission Electron Microscopy Techniques.

It is hard to directly visualize spectroscopic and atomic-nanoscopic information on the degraded Pt/C cathode layer inside polymer electrolyte fuel cell (PEFC). However, it is mandatory to understand the preferential area, sequence, and relationship of the degradations of Pt nanoparticles and carbon support in the Pt/C cathode layer by directly observing the Pt/C cathode catalyst for the development of next-generation PEFC cathode catalysts. Here, the spectroscopic, chemical, and morphological visualization of the degradation of Pt/C cathode electrocatalysts in PEFC was performed successfully by a same-view combination technique of nano-X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM)/scanning TEM-energy-dispersive spectrometry (EDS) under a humid N atmosphere.

Surface-Regulated Nano-SnO2/Pt3Co/C Cathode Catalysts for Polymer Electrolyte Fuel Cells Fabricated by a Selective Electrochemical Sn Deposition Method.

We have achieved significant improvements for the oxygen reduction reaction activity and durability with new SnO2-nanoislands/Pt3Co/C catalysts in 0.1 M HClO4, which were regulated by a strategic fabrication using a new selective electrochemical Sn deposition method. The nano-SnO2/Pt3Co/C catalysts with Pt/Sn = 4/1, 9/1, 11/1, and 15/1 were characterized by STEM-EDS, XRD, XRF, XPS, in situ XAFS, and electrochemical measurements to have a Pt3Co core/Pt skeleton-skin structure decorated with SnO2 nanoislands at the compressive Pt surface with the defects and dislocations.

Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

Mapping platinum species in polymer electrolyte fuel cells by spatially resolved XAFS techniques.

There is limited information on the mechanism for platinum oxidation and dissolution in Pt/C cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) under the operating conditions though these issues should be uncovered for the development of next-generation PEFCs. Pt species in Pt/C cathode catalyst layers are mapped by a XAFS (X-ray absorption fine structure) method and by a quick-XAFS(QXAFS) method. Information on the site-preferential oxidation and leaching of Pt cathode nanoparticles around the cathode boundary and the micro-crack in degraded PEFCs is provided, which is relevant to the origin and mechanism of PEFC degradation.

Performance and durability of Pt/C cathode catalysts with different kinds of carbons for polymer electrolyte fuel cells characterized by electrochemical and in situ XAFS techniques.

The electrochemical activity and durability of Pt nanoparticles on different kinds of carbon supports in oxygen reduction reactions (ORR) were investigated using rotating disc electrodes (RDE) and the membrane electrode assemblies (MEA) of polymer electrolyte fuel cells (PEFC). The mass activity of Pt/C catalysts (ORR activity per 1 mg of Pt) at the RDE decreased, according to the type of carbon support, in the following order; Ketjenblack (KB) > acetylene black (AB) > graphene > multiwall carbon nanotube (MW-CNT) > carbon black (CB), whereas the average size of the Pt nanoparticles and the surface specific activity (ORR activity per electrochemical surface area) did not vary significantly between these carbon supports. These results indicate that the different mass activities of the Pt/C catalysts may originate from the differences in the fraction of Pt on the carbon supports which is available for utilization.

Performance and characterization of a Pt-Sn(oxidized)/C cathode catalyst with a SnO2-decorated Pt3Sn nanostructure for oxygen reduction reaction in a polymer electrolyte fuel cell.

We have prepared and characterized a SnO2-decorated Pt-Sn(oxidized)/C cathode catalyst in a polymer electrolyte fuel cell (PEFC). Oxygen reduction reaction (ORR) performance of Pt/C (TEC10E50E) remained almost unchanged or even tended to reduce in repeated I-V load cycles, whereas the I-V load performance of the Pt-Sn(oxidized)/C prepared by controlled oxidation of a Pt-Sn alloy/C sample with the Pt3Sn phase revealed a significant increase with increasing I-V load cycles. The unique increase in the ORR performance of the Pt-Sn(oxidized)/C catalyst was ascribed to a promoting effect of SnO2 nano-islands formed on the surface of Pt3Sn core nanoparticles.

Uranyl-halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+.

Complexation of [UO2](2+) with Cl(-), Br(-), and I(-) in N,N-dimethylformamide (DMF) was studied by UV-vis absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) to clearly differentiate halide coordination strengths to [UO2](2+). In the Cl(-) system, it was clarified that the Cl(-) coordination to [UO2](2+) in DMF proceeds almost quantitatively. The coordination number of Cl(-) almost quantitatively increases up to 4, i.

Structure and stability range of a hexanuclear Th(IV)-glycine complex.

A hexanuclear Th(IV)-glycine complex was observed by Th L(3)-edge EXAFS measurements in an aqueous solution. Within the stability range of this complex the positively charged hexanuclear species [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)(H(2)O)(6)(Gly)(6)(HGly)(6)](6+) was preserved in a crystal with the composition [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)(H(2)O)(6)(Gly)(6)(HGly)(6)]·(NO(3))(3)(ClO(4))(3)(H(2)O)(3). This complex appears as a result of a competing reaction between hydrolysis and ligation by glycine.

Formation of soluble hexanuclear neptunium(IV) nanoclusters in aqueous solution: growth termination of actinide(IV) hydrous oxides by carboxylates.

Complexation of Np(IV) with several carboxylates (RCOO(-); R = H, CH(3), or CHR'NH(2); R' = H, CH(3), or CH(2)SH) in moderately acidic aqueous solutions was studied by using UV-vis-NIR and X-ray absorption spectroscopy. As the pH increased, all investigated carboxylates initiated formation of water-soluble hexanuclear complexes, Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4), in which the neighboring Np atoms are connected by RCOO(-)syn-syn bridges and the triangular faces of the Np(6) octahedron are capped with μ(3)-O(2-)/μ(3)-OH(-). The structure information of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) in aqueous solution was extracted from the extended X-ray absorption fine structure data: Np-O(2-) = 2.

Molecular structure and electrochemical behavior of uranyl(VI) complex with pentadentate Schiff base ligand: prevention of uranyl(V) cation-cation interaction by fully chelating equatorial coordination sites.

The U(VI) complex with a pentadentate Schiff base ligand (N,N'-disalicylidenediethylenetriaminate = saldien(2-)) was prepared as a starting material of a potentially stable U(V) complex without any possibility of U(V)O(2)(+)...

X-ray absorption fine structures of uranyl(V) complexes in a nonaqueous solution.

The structures of three different U(V) complexes, [U(V)O(2)(salophen)DMSO](-), [U(V)O(2)(dbm)(2)DMSO](-), and [U(V)O(2)(saldien)](-), in a dimethyl sulfoxide (DMSO) solution were determined by X-ray absorption fine structure for the first time.

Complex formation and molecular structure of neptunyl(VI) and -(V) acetates.

Stability and coordination of neptunyl(VI) and -(V) acetate complexes in aqueous solution were studied by using UV-vis-near-IR (NIR) and X-ray absorption fine structure (XAFS) spectroscopy. In the neptunyl(VI) acetate system, the formation of Np(VI)O(2)(AcO)(+), Np(VI)O(2)(AcO)(2)(aq), and Np(VI)O(2)(AcO)(3)(-) was detected. Both spectroscopic methods provided similar stability constants: log K(1) = 2.