A robust and active hybrid catalyst for facile oxygen reduction in solid oxide fuel cells

The sluggish oxygen reduction reaction (ORR) greatly reduces the energy efficiency of solid oxide fuel cells (SOFCs). Here we report our findings in dramatically enhancing the ORR kinetics and durability of the state-of-the-art La[subscript 0.6]Sr[subscript 0.4]Co[subscript 0.2]Fe[subscript 0.8]O[subscript 3](LSCF) cathode using a hybrid catalyst coating composed of a conformal PrNi[subscript 0.5]Mn[subscript 0.5]O[subscript 3](PNM) thin film with exsoluted PrOxnanoparticles. At 750°C, the hybrid catalyst-coated LSCF cathode shows a polarization resistance of ∼0.022 Ω cm[superscript 2], about 1/6 of that for a bare LSCF cathode (∼0.134 Ω cm[superscript 2]). Further, anode-supported cells with the hybrid catalyst-coated LSCF cathode demonstrate remarkable peak power densities (∼1.21 W cm[superscript -2]) while maintaining excellent durability (0.7 V for ∼500 h). Near Ambient X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-Ray Absorption Fine Structure (NEXAFS) analyses, together with density functional theory (DFT) calculations, indicate that the oxygen-vacancy-rich surfaces of the PrOxnanoparticles greatly accelerate the rate of electron transfer in the ORR whereas the thin PNM film facilitates rapid oxide-ion transport while drastically enhancing the surface stability of the LSCF electrode

Development and characterization of materials for intermediate temperature solid oxide fuel cell anodes

Solid Oxide Fuel Cells (SOFCs) are devices capable of directly converting chemical energy into electrical energy through high temperature electrochemical oxidation of fuels, but there remain serious obstacles before these devices can be fully implemented into the modern energy infrastructure. The operation of SOFCs with hydrocarbon fuels has the highest potential for commercial impact, but the activity of state-of-the-art materials toward these fuels is relatively low compared to hydrogen, and SOFCs can quickly degrade due to the deposition of solid carbon (coking). Lowering SOFC operating temperatures to less than 600 °C would expand the application of SOFCs while dramatically reducing system complexity and cost, but device performance at these temperatures remains prohibitively low. To address these obstacles, this work focuses on two key issues in SOFC technology development: improvement of SOFC materials and advancement of SOFC characterization techniques. First, a high performing SOFC was designed and demonstrated, uniquely suited for low temperature direct methane operation through the addition of an internal reforming catalyst layer. In situ spectroscopy was used extensively to evaluate the defect and surface structure of the reforming catalyst, directly relating the material structure to device performance. The second issue was addressed through the development of a novel testing platform for quantitative comparison of different anode surface coatings, as well as the design and fabrication of new operando equipment which increases the current testing capability of the SOFC community.Ph.D

Epitaxial and atomically thin graphene–metal hybrid catalyst films : the dual role of graphene as the support and the chemically-transparent protective cap

In this study, we demonstrate dual roles for graphene, as both a platform for large-area, fully-wetted growth of two-dimensional Pt films that are one monolayer to several multilayers thick, while also serving as a ‘chemically transparent’ barrier to catalytic deactivation wherein graphene does not restrict the access of the reactants but does block Pt from dissolution or agglomeration. Using these architectures, we show that it is possible to simultaneously achieve enhanced catalytic activity and unprecedented stability, retaining full activity beyond 1000 cycles, for the canonical oxygen reduction reaction (ORR). Using high resolution TEM, AFM, X-ray photoemission/absorption spectroscopy (XPS/XAS), Raman, and electrochemical methods, we show that, due to intimate graphene–Pt epitaxial contact, Pt_ML/GR hybrid architectures are able to induce a compressive strain on the supported Pt adlayer and increase catalytic activity for ORR. With no appreciable Pt loss or agglomeration observed with the GR/Pt_ML catalysts after 1000 ORR cycles, our results open the door to using similar graphene-templated/graphene-capped hybrid catalysts as means to improve catalyst lifetime without a necessary compromise to their activity. More broadly, the epitaxial growth made possible by the room-temperature, wetted synthesis approach, should allow for efficient transfer of charge, strain, phonons and photons, impacting not just catalysis, but also electronic, thermoelectric and optical materials

Functionalized Bimetallic Hydroxides Derived from Metal–Organic Frameworks for High-Performance Hybrid Supercapacitor with Exceptional Cycling Stability

A hybrid supercapacitor consisting of a battery-type electrode and a capacitive electrode could exhibit dramatically enhanced energy density compared with a conventional electrical double-layer capacitor (EDLCs). However, advantages for EDLCs such as stable cycling performance will also be impaired with the introduction of transition metal-based species. Here, we introduce a facile hydrothermal procedure to prepare highly porous MOF-74-derived double hydroxide (denoted as MDH). The obtained 65%Ni-35%Co MDH (denoted as 65Ni-MDH) exhibited a high specific surface area of up to 299 m² g^–1. When tested in a three-electrode configuration, the 65Ni-MDH (875 C g^–1 at 1 A g^–1) exhibited excellent cycling stability (90.1% capacity retention after 5000 cycles at 20 A g^–1). After being fabricated as a hybrid supercapacitor with N-doped carbon as the negative electrode, the device could exhibit not only 81 W h kg^–1 at a power density of 1.9 kW kg^–1 and 42 W h kg^–1 even at elevated working power of 11.5 kW kg^–1, but also encouraging cycling stability with 95.5% capacitance retention after 5000 cycles and 91.3% after 10 000 cycles at 13.5 A g^–1. This enhanced cycling stability for MDH should be associated with the synergistic effect of hierarchical porous nature as well as the existence of interlayer functional groups in MDH (proved by Fourier transform infrared spectroscopy (FTIR) and in situ Raman spectroscopy). This work also provides a new MOF-as-sacrificial template strategy to synthesize transition metal-based hydroxides for practical energy storage applications

Bioenabled Core/Shell Microparticles with Tailored Multimodal Adhesion and Optical Reflectivity

Nature provides remarkable examples of mass-produced microscale particles with structures and chemistries optimized by evolution for particular functions. Synthetic chemical tailoring of such sustainable biogenic particles may be used to generate new multifunctional materials. Herein, we report a facile method for the development of bioenabled core/shell microparticles consisting of surface-modified ragweed pollen with a magnetic core, for which both multimodal adhesion and optical reflectivity can be tailored. Adhesion of the magnetic-core pollen can be tuned, relative to native pollen, through the combination of tailorable short-range interactions (over ∼5 nm, via van der Waals forces and hydrogen bonding), an intermediate-range (over several μm) capillary force, and long-range (over ∼1 mm) magnetic attraction. The magnetic force could be controlled by the amount of iron oxide loaded within the core of the pollen particle, while the short-range interactions and capillary force can be tuned by coating with polystyrene nanoparticles and/or a layer of viscous pollenkitt on the exine shell surface. Such coatings were also used to tailor the optical reflectance of the magnetic pollen particles; that is, the light-reflectance intensity was enhanced by coating with pollenkitt and significantly reduced by coating with polystyrene nanoparticles. This approach for generating multifunctional core/shell microparticles with tailorable adhesion and optical reflectivity may be extended to other pollen or biological particles or to synthetic biomimetic particles. Such independent control of the core and shell chemistries enabled by this approach also allows for the generation of microparticles with a variety of combination in functions tailorable to other properties

Epitaxial and atomically thin graphene–metal hybrid catalyst films: the dual role of graphene as the support and the chemically-transparent protective cap

In this study, we demonstrate dual roles for graphene, as both a platform for large-area, fully-wetted growth of two-dimensional Pt films that are one monolayer to several multilayers thick, while also serving as a 'chemically transparent' barrier to catalytic deactivation wherein graphene does not restrict the access of the reactants but does block Pt from dissolution or agglomeration. Using these architectures, we show that it is possible to simultaneously achieve enhanced catalytic activity and unprecedented stability, retaining full activity beyond 1000 cycles, for the canonical oxygen reduction reaction (ORR). Using high resolution TEM, AFM, X-ray photoemission/absorption spectroscopy (XPS/XAS), Raman, and electrochemical methods, we show that, due to intimate graphene-Pt epitaxial contact, Pt-ML/GR hybrid architectures are able to induce a compressive strain on the supported Pt adlayer and increase catalytic activity for ORR. With no appreciable Pt loss or agglomeration observed with the GR/Pt-ML catalysts after 1000 ORR cycles, our results open the door to using similar graphene-templated/graphene-capped hybrid catalysts as means to improve catalyst lifetime without a necessary compromise to their activity. More broadly, the epitaxial growth made possible by the room-temperature, wetted synthesis approach, should allow for efficient transfer of charge, strain, phonons and photons, impacting not just catalysis, but also electronic, thermoelectric and optical materials