Heterogeneous Functional Materials Research Articles

(Invited) Design of Ceramic Fuel Electrode for Solid Oxide Cells for Direct Oxidation of Hydrocarbon Fuels and for Direct CO2 Electrolysis

Large scale consumption of fossil fuels has led to the rapid increase in the atmospheric CO2 concentration, resulting in very adverse environmental concerns and frequent natural disasters. There is a grand challenge to improve conversion efficiency of fossil fuels and mitigate CO2 emmissions for terrestial applications. To enable long-term manned space exploration, there are critical needs in recycling CO2 to oxygen for life support and in situ generation of propellants using CO2 feedstock for ascent vehicles. Solid oxide cells (SOCs) have a great promise for energy conversion and storage for both terrestrial applications and space explorations. In the fuel cell mode, SOCs can convert chemical energy to electrical energy with high efficiency and fuel flexibility. In the electrolysis mode, SOCs can efficiently utilize CO2 as feedstock for chemical synthesis. The conventional Ni-based fuel electrode is vulnerable to deactivation by carbon build-up (coking) from direct oxidation of hydrocarbon fuels or for direct electrolysis of CO2, and suffers volume instability on redox cycling. This talk will report novel heterogeneous functional materials as SOC fuel electrodes that possess a combined property of good coking resistance and redox cyclability, enabling SOCs to be operated on hydrocarbon fuels for electricity generation in the fuel cell mode and for direct CO2 electrolysis for fuel synthesis in the electrolysis mode.The general philosophy to design novel SOC fuel electrodes is to develop ceramic materials that are redox-stable, possess mixed ionic and electronic mixed conductivity, and have catalytic activities for fuel oxidation and CO2 splitting reaction. Different types of ceramic fuel electrode materials have been explored and characterized as SOC fuel electrodes. The phase formation, redox-stability, electrical conductivity, electrochemical performance, and tolerance to coking and redox-cycling have been systematically evaluated. By judicious design of ceramic-based heterogeneous functional materials, high performance redox-flexible ceramic fuel electrodes can be achieved for direct oxidation of hydrocarbon fuels and for direct CO2 electrolysis. Acknowledgements Financial support from the U.S. Department of Energy (DE-EE0009427), National Science Foundation (DMR–1832809) and NASA EPSCoR (Grant # 80NSSC20M0233) is greatly appreciated.

(Opening Keynote) Heterogeneous Functional Materials: Their Present Science and Engineering, and Their Role in the Future of Our Society

Devices that convert and store energy are generally made from heterogeneous constituent materials that act and interact to selectively conduct, transport, and regulate mass, heat, and charge. Controlling these functional actions and interactions enables the technical breakthroughs that have made high efficiency fuel cells, batteries, and solid state membranes, for example, essential parts of our society and economy. In the biological sense, these materials are ‘vascular’ rather than primitive ‘cellular’ materials, so that the arrangements and configurations of the constituents play essential roles in their functional capabilities. Local interactions of the constituents create “emergent” properties and responses that are not part of the formal set of constituent characteristics, in much the same sense that society and culture is created by the group interactions of the people involved. The design of emergent properties is an open question in all formal science, but for energy materials the lack of this foundation science relegates development tasks to Edisonian trial and error, with anecdotal success and frequent costly failures. The present group has defined, for the first time, multi-scale heterogeneous functional materials with functional disordered and void phase regions as “HeteroFoaM,” and formed the first multidisciplinary research team (EFRC) to define and codify the foundation science of that material class. The primary goal of the HeteroFoaM Center was, and the continuing interest is, to create and establish the multi-scale fundamental knowledge and related methodology required for the rational and systematic multiphysics design of heterogeneous functional materials and their interfaces and surfaces for applications in energy transformation and storage. HeteroFoaM is a new atoms-to-systems paradigm that is intended to bring heterogeneous functional materials (for which the system is rarely simply the sum of the parts) into the modern age of computational materials to achieve the savings of time and cost associated with trial and error Edisonian design.The promise of this pursuit is to construct a Multi-Scale/Multi-Physics (M2SP) Design Science for Heterogeneous Functional Materials that is codified in models and codes that enable the design of material systems to convert fuels directly into electricity, store energy in easily transported forms, and separate strategic materials including nuclear waste.The HeteroFoaM paradigm is an approach that focuses on the “conformal science” that defines the local interactions that result from the arrangements and configurations of the constituents. The approach fully embraces the complexity of heterogeneous functional material systems including the uncertainty of predictions and observations, the creation of a formal structure for combining analysis, simulations, and experiments, and the creation of a science path to the prediction of emergent global response probabilities based on the local or meso-science of constituent interactions. However, since this concept was originated almost 10 years ago, a technical revolution has happened in our world society that makes progress in this field even more imperative. There has been an historic shift in our society to hydrogen as a preferred fuel, with industrial and governmental promises that it will be nearly an exclusive choice for society and industry in the next ten years or so. Therefore, our discussion will begin with the historic foundations of this field and end with a short summary of the remarkable and historic changes in society that have elevated this subject to a central and critical science and engineering subject for our world society today.

(Invited) From Nano-Bulk Interplayed Composites to Industrial Standard Devices: A Length Scale Evolution of Heterogeneous Functional Materials for Solid Oxide Electrochemical Cells at Intermediate Temperatures

Heterogeneous functional materials play very important roles in solid oxide electrochemical cells in intermediate temperatures (400-600oC). At this temperature regime, the solid oxide electrochemical cells can compromise the disadvantages from lower and higher temperature counterparts by adopting more cost-effective catalysts and materials as the cell components while mitigating the fast degradation to achieve optimal reaction kinetics. More importantly, it allows many nano-sized catalysts to be functioning that can be ultimately integrated into the real device through advanced manufacturing technologies. At Idaho National Laboratory, we developed a series of strategies to accommodate heterogeneous functional materials for a range of applications, including hydrogen production via water electrolysis, CO2 conversion and ammonia electrosynthesis using protonic ceramic electrochemical cells (PCECs). The special emphasis is placed on the effect of structure, composition, morphology, and defects of these materials on electrochemical performance of PCECs and respective product for a given feedstock.

(Invited, Digital Presentation) Phase Interactions and Degradation in Battery Composite Electrodes

The composite electrodes of lithium-ion and sodium-ion batteries must balance complex interactions between the many physical phenomena that underpin battery operation. Active materials host electroactive species. Porous regions support the movement of ions, and secondary phases containing binders and conductive additives provide a supporting electron conducting matrix. Cycling and aggressive operating conditions drive changes in these phases and the balance between them. The alteration of these electrode phases manifests in declining performance and ultimately battery failure. Here, we present an overview of research on degradation processes observed in a diverse set of battery materials using X-ray imaging methods—nanotomography, microtomography, and X-ray absorption near edge structure (XANES) imaging—complemented by electrochemical experiments and other materials characterization methods.Metallic anodes offer a high-capacity alternative to carbon-based anodes for lithium-ion and sodium-ion batteries. Among these metallic anodes tin-based active materials present high-capacity and electrochemical activity in both lithium and sodium chemistries. However, high capacity comes at the price of excessive volume expansion and attendant performance degradation. Studies of Cu6Sn5 alloy anodes in lithium-ion batteries performed using X-ray tomography and nanoscale 2D XANES reveal material volume expansion, fracture, and dissolution as key failure mechanisms within the active material. However, the expansion and contraction of the metallic active material during cycling also leads to significant changes in the supporting carbon-binder domains of the electrodes. Such changes are also observed in the cycling of tin-based composite anodes in both lithium-ion and sodium-ion applications. Active material pulverization of tin due to lithiation and sodiation processes is evident in phase size distributions observed with X-ray microtomography. These changes are accompanied by alteration of the supporting carbon-binder regions.Low cobalt layered oxide cathode materials for lithium-ion batteries present an opportunity for maintaining desirable theoretical capacities while removing cobalt, a metal that presents significant humanitarian issues within its supply chain. However, removal of cobalt from these layered oxide systems removes its stabilizing influence on the electrode structure, especially when cycling at voltages above 4.0 V vs. Li/Li+. Degradation of the low cobalt cathode material Li(Ni0.8Mn0.1Co0.1)O2 has been assessed under different cut-off voltage and operating temperatures using a suite of electrochemical and materials characterization techniques. Higher cycling temperature was found to accelerate degradation mechanisms within the active material, specifically rock-salt phase formation and active material dissolution. Elevated temperature was found to cause significant changes in the supporting carbon-binder domains as well. These changes in both the active material and supporting phases manifest in degradation of electrochemical performance with respect to lost capacity and altered electrode impedances.Taken together, the above studies provide a picture of battery degradation that is driven by anticipated changes in the active material and more nuanced variations that occur in the supporting phases. These observations motivate holistic approaches for the analysis and design of battery electrodes that fit their status as heterogeneous functional materials.

(Invited, Digital Presentation) Understanding Interfacial Chemo-Mechanics of Two-Dimensional Materials-Based Heterogeneous Functional Materials for Energy Storage

Two-dimensional (2D) materials and their heterostructures (2D + nD, n = 0,1,2,3) attracted enormous interest in wide range of applications including electrochemical systems, e.g., batteries. Electro-chemo-mechanics, the coupling of mechanics and electrochemistry, plays a crucial role in designing these systems. This talk considers battery as a model system and demonstrates the role of 2D materials in overcoming various interfacial electro-chemo-mechanical challenges. 2D materials are engineered as the van der Waals (vdW) “slippery” interface. For example, silicon (Si) electrodes can be placed over the graphene-coated current collector for Lithium-Ion Batteries (LIBs). This arrangement provides less stress build-up and less stress “cycling” on the vdW slippery substrate instead of a fixed interface. 2D materials such as MXenes can also be used to replace polymer binders, e.g., in Si-based LIBs. Our DFT studies show more stable performance and higher Coulombic efficiency for Si films deposited on graphene-coated nickel (i.e., slippery interface) than conventional nickel current collectors. The interface strength of monoclinic Se (selenium) is 0.43 J/m2, which is similar in magnitude in amorphous Si with graphene (0.41 J/m2). However, the interface strength of c-Se on a 3D aluminum (Al) current collector is higher (0.99 J/m2), suggesting a stronger adhesion for 3D/3D interface than 3D/2D interface. Furthermore, interface strength variation between a-Si and Ti3C2Tx MXenes are determined for various surface functional groups (Tx). The completely hydroxylated Ti3C2 has the highest interface strength of 0.60 J/m2 with a-Si. The talk also summarizes our recent efforts in developing High Dimensional Deep Learning Potential (HDDLP) to study interfacial electro-chemo-mechanics in 2D materials-based systems. Our computational results are in good agreement with experiments. Besides batteries, our comprehensive interface analyses are beneficial in advancing understanding of other 2D materials-based systems, e.g., sensors, fuel cells, solar cells, nanomedicine, soft-actuators, etc.

Creating three-dimensional magnetic functional microdevices via molding-integrated direct laser writing

Magnetically driven wireless miniature devices have become promising recently in healthcare, information technology, and many other fields. However, they lack advanced fabrication methods to go down to micrometer length scales with heterogeneous functional materials, complex three-dimensional (3D) geometries, and 3D programmable magnetization profiles. To fill this gap, we propose a molding-integrated direct laser writing-based microfabrication approach in this study and showcase its advanced enabling capabilities with various proof-of-concept functional microdevice prototypes. Unique motions and functionalities, such as metachronal coordinated motion, fluid mixing, function reprogramming, geometrical reconfiguring, multiple degrees-of-freedom rotation, and wireless stiffness tuning are exemplary demonstrations of the versatility of this fabrication method. Such facile fabrication strategy can be applied toward building next-generation smart microsystems in healthcare, robotics, metamaterials, microfluidics, and programmable matter.

Transient Anomalous Diffusion MRI Measurement Discriminates Porous Polymeric Matrices Characterized by Different Sub-Microstructures and Fractal Dimension.

Considering the current development of new nanostructured and complex materials and gels, it is critical to develop a sub-micro-scale sensitivity tool to quantify experimentally new parameters describing sub-microstructured porous systems. Diffusion NMR, based on the measurement of endogenous water’s diffusion displacement, offers unique information on the structural features of materials and tissues. In this paper, we applied anomalous diffusion NMR protocols to quantify the subdiffusion of water and to measure, in an alternative, non-destructive and non-invasive modality, the fractal dimension dw of systems characterized by micro and sub-micro geometrical structures. To this end, three highly heterogeneous porous-polymeric matrices were studied. All the three matrices composed of glycidylmethacrylate-divynilbenzene porous monoliths obtained through the High Internal Phase Emulsion technique were characterized by pores of approximately spherical symmetry, with diameters in the range of 2–10 μm. Pores were interconnected by a plurality of window holes present on pore walls, which were characterized by size coverings in the range of 0.5–2 μm. The walls were characterized by a different degree of surface roughness. Moreover, complementary techniques, namely Field Emission Scanning Electron Microscopy (FE-SEM) and dielectric spectroscopy, were used to corroborate the NMR results. The experimental results showed that the anomalous diffusion α parameter that quantifies subdiffusion and dw = 2/α changed in parallel to the specific surface area S (or the surface roughness) of the porous matrices, showing a submicroscopic sensitivity. The results reported here suggest that the anomalous diffusion NMR method tested may be a valid experimental tool to corroborate theoretical and simulation results developed and performed for describing highly heterogeneous and complex systems. On the other hand, non-invasive and non-destructive anomalous subdiffusion NMR may be a useful tool to study the characteristic features of new highly heterogeneous nanostructured and complex functional materials and gels useful in cultural heritage applications, as well as scaffolds useful in tissue engineering.

Heterogeneous Reaction Mechanisms and Functional Materials for Elemental Mercury Removal from Industrial Flue Gas

Heterogeneous Reaction Mechanisms and Functional Materials for Elemental Mercury Removal from Industrial Flue Gas

Synergetic Advantages of Atomically Coupled 2D Inorganic and Graphene Nanosheets as Versatile Building Blocks for Diverse Functional Nanohybrids.

2D nanostructured materials, including inorganic and graphene nanosheets, have evoked plenty of scientific research activity due to their intriguing properties and excellent functionalities. The complementary advantages and common 2D crystal shapes of inorganic and graphene nanosheets render their homogenous mixtures powerful building blocks for novel high-performance functional hybrid materials. The nanometer-level thickness of 2D inorganic/graphene nanosheets allows the achievement of unusually strong electronic couplings between sheets, leading to a remarkable improvement in preexisting functionalities and the creation of unexpected properties. The synergetic merits of atomically coupled 2D inorganic-graphene nanosheets are presented here in the exploration of novel heterogeneous functional materials, with an emphasis on their critical roles as hybridization building blocks, interstratified sheets, additives, substrates, and deposited monolayers. The great flexibility and controllability of the elemental compositions, defect structures, and surface natures of inorganic-graphene nanosheets provide valuable opportunities for exploring high-performance nanohybrids applicable as electrodes for supercapacitors and rechargeable batteries, electrocatalysts, photocatalysts, and water purification agents, to give some examples. An outlook on future research perspectives for the exploitation of emerging 2D nanosheet-based hybrid materials is also presented along with novel synthetic strategies to maximize the synergetic advantage of atomically mixed 2D inorganic-graphene nanosheets.

Evaluation of functionality in Ni@stabilized ZrO2 and NiO@NiO–Zn through X-ray diffraction technique

A mathematical model is developed for calculating X-ray penetration depth based on the theories of diffraction to quantitatively characterize the heterogeneous functional materials with core-shell morphology. Functional materials viz. Ni@stabilized ZrO2 (SZ) and NiO@NiO–Zn are synthesized and penetration depth (ξNi/ξNiO) is calculated. Ni@SZ and NiO@NiO–Zn function as effective catalyst for methane steam reformation and olefin epoxidation respectively. Functionality of the catalysts lies in the core-shell morphology with interconnection among the phases. The author's aim to optimize the shell thickness using the mathematical model and correlate with the catalyst activity. Sequential increase of Ni-content in Ni@SZ from 25 to 40 vol % results in reduction of penetration depth [~2.1 to 0.8 μm] relative to core (ξSZ-core) thereby restricting the SZ contribution and limiting the oxide ion percolation. Similarly, surface coverage of nano NiO onto NiO–Zn for olefine epoxidation requires the involvement of three zone region viz. NiO, Zn and pi electron cloud of the substrate. Effectivity of the catalytic activity of such NiO@NiO–Zn matrix is found optimum (4.3 μm w.r.t.ξNiO) with the penetration depth derived from mathematical modeling. Hence, such modeling reveals its significance towards finding the penetration depth for core-shell type functional materials for catalysis compared to disperse heterogeneous catalyst.

Preface—JES Focus Issue on Heterogeneous Functional Materials for Energy Conversion and Storage

Preface—JES Focus Issue on Heterogeneous Functional Materials for Energy Conversion and Storage

Optical study of Au/Ti/Ni/Mg-nanoparticles decorated zinc oxide heterostructures: size effect induced modulation of work function

The development of the novel semiconductor heterogeneous functional materials is playing an ever more important role in materials and efficient devices with new properties and functions. In this work, heterostructures of Au/Ti/Ni decorated zinc oxide nanobelts were synthesized. The amount and diameter of metal nanoparticles were controlled by the sputtering time or the deposition time. The photoluminescence of metal/ZnO heterostructures has been investigated. Very strong enhancement of near-band-edge emission and simultaneous attenuation of visible emission were observed for ZnO nanobelts decorated with Au, Ti and Ni nanoparticles. But both the NBEUV and DL emission intensities of Ni/ZnO heterostructures decrease dramatically initially. A novel mechanism is proposed to explain observed kinds of experimental results based on characteristic of metal nanoparticles, LSPR, Purcell effects and work function change of nanosize induced. The Mg decorated zinc oxide nanobelts were synthesized for the first time. Then the entire mechanism was testified by the investigation on Mg/ZnO and Ni/ZnO heterostructures due to its much lower and higher work functions compared with that of ZnO nanobelts, respectively. The mechanism will facilitate the technical application of metal-nanoparticles decorated heterostructures, and be very useful for the creation of highly efficient optoelectronic devices.

Morphology Drivers for Irreversible Species Diffusion and Transport in HeteroFoaMs

This paper presents recent advances in our understanding of how structure (at all scale levels) influences and in many cases controls selected properties and performance of heterogeneous functional materials (HeteroFoaMs). We begin with mesomorphology and surface/volume discussions, and conclude with methods and concepts that start at the atomic level. Special attention is given not only to equilibrium processes but also to nonequilibrium behavior that controls, for example, the confinement of nuclear waste products. Surface to volume transitions and other principles are identified. The paper is written in outline form, with the purpose of identifying principles for further study. The significance of the findings is illustrated with discussions of applications to composite structures, nuclear fuel storage materials, functional materials used in electronics, oxide thin films, and batteries.

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers.

The performance of ion-conducting polymer membranes is complicated by an intricate interplay between chemistry and morphology that is challenging to understand. Here, we report on perfuoroionene chain extended (PFICE) ionomers that contain either one or two bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers exhibit greater water uptake and conductivity compared to prototypical perfluorinated sulfonic acid ionomers. Advanced in situ synchrotron characterization reveals insights into the connections between molecular structure and morphology that dictate performance. Guided by first-principles calculations, X-ray absorption spectroscopy at the sulfur K-edge can discern distinct protogenic groups and be sensitive to hydration level and configurations that dictate proton dissociation. In situ resonant X-ray scattering at the sulfur K-edge reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated states. The enhanced conductivity of PFICE ionomers is attributed to a unique multi-acid side-chain chemistry and structure that facilitates proton dissociation at low water content in combination with a well-ordered phase-separated morphology with nanoscale transport pathways. Overall, these results provide insights for the design of new ionomers with tunable phase separation and improved transport properties as well asdemonstrating the efficacy of X-rays with elemental sensitivity for unraveling structural features in chemically heterogeneous functional materials for electrochemical energy applications.

(Keynote) Emergent Effects of Global Surfaces on Local Microstructure Designs for Functionality in Heterogeneous Functional Materials

Heterogeneous functional materials are of special importance to the design of functional devices such as fuel cells, batteries, and capacitors, but they are also critical to applications like energy storage and the confinement of nuclear waste materials. Morphology design is critical to all of these (and other) applications, and much literature records the science and engineering of that subject. But the rules we generate and recite that control particle / void space and shape, surface to volume / phase shape selections, constituent distributions and other aspects of those microstructure designs do not predict the emergent properties and functionalities of such materials when a global surface influences or controls the basic transport or diffusion of active species into and out of those microstructures when they act as functional materials. Examples of such emergent properties and functionalities will be identified and discussed in the present paper, with the intent of identifying general concepts and principles that help us to design successful microstructures in those situations. Subjects of the discussion will include threshold volume fractions, short vs. long term response, surface to volume ratios, interface / interphase effects, and critical path concepts. Examples will be provided from several application fields, and some directions will be suggested.

(Invited) Understanding Heterogeneous Functional Materials Via Scale-Bridging between Nano and Micro Transmission x-Ray Microscopy and Absorption Near Edge Structure

Heterogeneous functional materials for energy-conversion and –storage, such as fuel cells, electrolyzers and batteries are hierarchical, porous, electroactive materials that rely on multi-scale imaging techniques for accurate morphological characterization. These materials are building blocks for the catalyst layers, gas diffusion layers and electrodes in fuel cells, porous transport layers (PTLs) in electrolyzers and porous electrodes within batteries. Functional materials electrochemical functionality can be assessed with various in-situ and operando techniques that probe chemical state during operation, such as x-ray absorption near edge structure (XANES). Synchrotron bright x-ray sources allow for nano-scale imaging combined with XANES, which state-of-the-art lab-scale systems are still lacking. Furthermore, these bright sources allow ultra-fast imaging on sub-second and micro-second temporal resolution. Optimization of temporal, spatial and chemical dimensions is critical to answer the morphological and chemical questions of interest [1]. Transmission x-ray microscopy (TXM) and its three-dimensional analog x-ray computed tomography (CT) allows 30 nm resolution with nano-CT set-up and 1 um resolution with micro-CT beamlines. The nano-CT beamlines have precise energy resolution to enable a combination of 3D imaging and XANES. The generated imaging data sizes exceed terabytes of space and requires modeling frameworks to interpret the findings. We have developed a scale-bridging algorithm to incorporate nano-scale findings into micro-scale using direct numerical simulations and coupling algorithms via effective properties and boundary conditions. In this work we will present several examples of operando data collected on fuel cells, electrolyzers and batteries using nano and micro x-ray CT and in some instances with XANES or with sub-second radiography. Full-field x-ray imaging beamline 18-ID at National Synchrotron Light Source II has achieved 3 minutes nano-CT scan, what enables full 3D XANES scan within reasonable time-frame. Some of the questions that we attempt to answer include activity and water management of NiCu/KB electrocatalyst used in alkaline fuel cells as anode; electrocatalyst activity and its interface with the PTL within operating electrolyzers, and Li metal dendrite growth in solid polymer electrolyte batteries during cycling. Scale-bridging framework is applied to fuel cell electrodes to understand oxygen transport and reaction-diffusion processes for these multi-scale catalyst layers.

(Invited) Probing the Structure and Dynamic Behaviors of Heterogeneous Functional Materials with the Atomic Resolution in Real-Time

The recent advancement of aberration-corrected transmission electron microscopy (TEM) and in situ techniques unlocks a door to a new era of discovery in materials science. It allows us to study the local structure, chemical composition, and electronic properties of nanostructures with the atomic resolution, and observe the dynamic evolution of materials in response to applied fields and to changes in environments in real-time. In this talk, I will present our work on the development of in-situTEM techniques for imaging electric polarization, probing the nucleation and growth of ferroelectric domains during electric polarization switching, and observing thedynamic reaction and structural evolution of heterogeneous functional materials under realistic conditions with atomic precisionthrough a MEMS-based, electron-transparent closed cell with a heating stage.

Three-Dimensional Analysis of Coarsening Dynamics in Porous Materials for Electrochemical Energy Conversion and Storage: Direct Measurement and Visualization of Changes in Local Surface Curvature

High operating temperature affords solid oxide fuel cells (SOFCs) fuel flexibility, favorable kinetics, enhanced transport properties and high quality heat for secondary thermodynamic cycles.1 Elevated temperatures, however, present challenges to ensuring cell durability.2 Coarsening of nickel in the Ni-YSZ anode is one such challenge that can lead to significant performance degradation. The fundamental driving force Δμ for coarsening phenomena is given by Eq. 1.3 The expression, which assumes isotropic interfacial energy, indicates that the chemical potential μ of a curved interface differs from that of a flat interface μ 0 by the factor VmγH, where H is mean curvature, γ interfacial energy and Vm molar volume. Δμ = μ - μ 0 = VmγH (1) Eq. 1 makes evident that variations in interface curvature, i.e., interface shape, directly correspond to variations in chemical potential. Furthermore, it follows from Eq. 1 that microstructural coarsening is fundamentally related to variations in interface shape. The link between interface shape and coarsening propensity is well known and methods have been developed to directly measure interfacial curvature distributions for complex morphologies in 3-D.4,5 In this work, these techniques are applied to 3-D images obtained by x-ray nanotomography to study coarsening in microstructures obtained from Ni-YSZ solid oxide fuel cell anodes aged for varying lengths of time. This work builds on a previous characterization of the same samples.6 The curvature measurements collected suggest that a combination of coarsening and morphological instability, which leads to channel pinch-off, severely diminish the connectivity of the anode’s Ni network and, in addition, lead to a significant loss of both nominal and effective triple-phase boundary (TPB) density. Both the loss of connectivity and TPB density coincide with cell performance degradation that was observed in the aging experiment7 from which the anode samples were taken. References Singhal, S. C.; Kendall, K. High Temperature Solid Oxide Fuel Cells, Elsevier, 2003.Yokokawa, H.; Tu, H.; Iwanschitz, B.; Mai, A. Fundamental mechanisms limiting solid oxide fuel cell durability. J. Power Sources 2008, 400-412.Voorhees, P. W. The Theory of Ostwald Ripening. J. Stat. Phys. 1985, 231-252.Glicksmann, M. E.; Voorhees, P. W. Ostwald Ripening and Relaxation in Dendritic Structures. Metall. Trans. A, 1984, 995-1001.Mendoza, R.; Savin, I.; Thornton, K.; Voorhees, P. W. Topological complexity and the dynamics of coarsening. Nat. Mater., 2004 385-388.Nelson, G. J.; Grew, K. N.; Izzo, J. R. Jr.; Lombardo, J. J.; Harris, W. M.; Faes, A.; Hessler-Wyser, A.; Van herle, J.; Wang, S.; Chu, Y. S.; Virkar, A. V.; Chiu, W. K. S. Three-dimensional microstructural changes in the Ni-YSZ solid oxide fuel cell anode during operation. Acta Mater., 2012 3491-3500. 7. Faes, A.; Hessler-Wyser, A.; Presvytes, D.; Vayenas, C. G.; Van herle, J. Nickel-Zirconia Anode Degradation and Triple Phase Boundary Quantification from Microstructural Analysis. Fuel Cells, 2009 841-851. Acknowledgements Financial support from the National Science Foundation (Award CBET-1134052) and an Energy Frontier Research Center on Science Based Nano-Structure Design and Synthesis of Heterogeneous Functional Materials for Energy Systems (HeteroFoaM Center) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award DE-SC0001061) is gratefully acknowledged. X-ray nanotomography was performed with Dr. Steve Wang at the Advanced Photon Source supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Ni-YSZ samples were provided by MER Dr. J. Van herle (Ecole Polytechnique Federale de Lausanne, Switzerland).

Validated predictive computational methods for surface charge in heterogeneous functional materials: HeteroFoaM™

Abstract Background Essentially all heterogeneous materials are dielectric, i.e., they are imperfect conductors that generally display internal charge displacements that create dissipation and local charge accumulation at interfaces. Over the last few years, the authors have focused on the development of an understanding of such behaviour in heterogeneous functional materials for energy conversion and storage, called HeteroFoaM (www.HeteroFoaM.com). Using paradigm problems, this work will indicate major directions for developing generally applicable methods for the multiphysics, multi-scale design of heterogeneous functional materials. Methods The present paper outlines the foundation for developing validated predictive computational methods that can be used in the design of multi-phase heterogeneous functional materials, or HeteroFoaM, as a genre of materials. Such methods will be capable of designing not only the constituent materials and their interactions, but also the morphology of the shape, size, surfaces and interfaces that define the heterogeneity and the resulting functional response of the material system. Results Relationships to applications which drive this development are identified. A paradigm problem based on dielectric response is formulated and discussed in context. Conclusions We report an approach that defines a methodology for designing not only the constituent material properties and their interactions in a heterogeneous dielectric material system, but also the morphology of the shape, size, surface, and interfaces that defines the heterogeneity and the resulting functional response of that system.

Simultaneous multiplexed materials characterization using a high-precision hard X-ray micro-slit array.

The needs both for increased experimental throughput and for in operando characterization of functional materials under increasingly realistic experimental conditions have emerged as major challenges across the whole of crystallography. A novel measurement scheme that allows multiplexed simultaneous measurements from multiple nearby sample volumes is presented. This new approach enables better measurement statistics or direct probing of heterogeneous structure, dynamics or elemental composition. To illustrate, the submicrometer precision that optical lithography provides has been exploited to create a multiplexed form of ultra-small-angle scattering based X-ray photon correlation spectroscopy (USAXS-XPCS) using micro-slit arrays fabricated by photolithography. Multiplexed USAXS-XPCS is applied to follow the equilibrium dynamics of a simple colloidal suspension. While the dependence of the relaxation time on momentum transfer, and its relationship with the diffusion constant and the static structure factor, follow previous findings, this measurements-in-parallel approach reduces the statistical uncertainties of this photon-starved technique to below those associated with the instrument resolution. More importantly, we note the potential of the multiplexed scheme to elucidate the response of different components of a heterogeneous sample under identical experimental conditions in simultaneous measurements. In the context of the X-ray synchrotron community, this scheme is, in principle, applicable to all in-line synchrotron techniques. Indeed, it has the potential to open a new paradigm for in operando characterization of heterogeneous functional materials, a situation that will be even further enhanced by the ongoing development of multi-bend achromat storage ring designs as the next evolution of large-scale X-ray synchrotron facilities around the world.