Chemistry, Department of

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Electrochemically Aged Ni Electrodes Supporting NiFe2O4 Nanoparticles for the Oxygen Evolution Reaction

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-11-26
Abstract: 

The preparation and screening of nanoparticle (NP) electrocatalysts for improved electrocatalytic oxygen evolution reactions (OER) will require a better understanding and optimization of the interactions between NPs and their support. First-row transition metals are used extensively as electrocatalysts in electrochemical energy storage and conversion systems. These electrocatalysts undergo transformations in their phase and surface morphology, which are induced by oxidizing potentials in the alkaline medium. A template-assisted approach to prepare electrodes with regular surface morphologies was used to monitor interactions between the NPs and their support both before and after prolonged electrochemical aging. A template-assisted method was used to prepare uniform surface inclusions of nickel ferrite (NiFe2O4) NPs on conductive nickel (Ni) supports for evaluation toward the OER. Electron microscopy-based methods were used to assess the resulting transformations of the embedded NPs within the Ni support matrix. Electrochemical aging of these textured electrodes was conducted by cyclic voltammetry (CV) techniques, which resulted in the growth of a 200 nm thick Ni oxy(hydroxide) film on the surfaces of the Ni supports. The growth of the active surface layer led to the encapsulation of the NiFe2O4 NPs as determined by correlative energy dispersive X-ray spectroscopy (EDS) techniques. The NP-modified electrodes exhibited reduced overpotentials and higher sustained current densities for the OER when compared to pure Ni supports. The well-defined morphologies and NP surface inclusions prepared by the template-assisted approach could serve as a platform for investigating additional NP–support interactions for electrocatalytic systems.

Document type: 
Article

Patterning Catalyst Layers with Microscale Features by Soft Lithography Techniques for Proton Exchange Membrane Fuel Cells

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2020-01-02
Abstract: 

Microtransfer molding (µTM) and microcontact printing (µCP) techniques were demonstrated for the preparation of platinum based catalysts in hexagonally arranged patterns to achieve cathode catalyst layers (CCLs) with microscale patterned features. These soft lithographic techniques, previously demonstrated for use in the preparation of patterned thin films, were adopted to produce patterned CCLs for proton exchange membrane fuel cells (or PEMFCs) with features having a thickness up to 20 µm. The resulting CCLs contained precise microscopic patterns that could be tuned for improving the performance of PEMFCs. It was demonstrated that CCLs containing arrays of microscale, cylindrical holes as prepared by µTM exhibited an improvement in their water management characteristics within PEMFCs when compared to CCLs prepared from continuous catalyst films. Upon further tuning of the CCL transfer procedures for µCP of CCLs, the formation of isolated microscale, disc-like features were demonstrated to have twice the mass activity of that observed for PEMFCs containing CCLs with uniform thin catalyst films. These methods to prepare patterned CCLs are compatible with current manufacturing techniques and could be easily adapted to incorporate other catalyst materials for further improvements in PEMFC performance. The soft lithography techniques used herein could also be scaled up to meet the industrial demand of large volume manufacturing.

Document type: 
Article

SU-8 and PDMS-based Hybrid Fabrication Technology for Combination of Permanently Bonded Flexible and Rigid Features on a Single Device

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-05-16
Abstract: 

In this article, a novel hybrid fabrication technology is presented that uses both a flexible polymer (polydimethylsiloxane-–PDMS) and a rigid polymer (SU-8). A covalent bond between the flexible and rigid polymer layers is achieved using an oxygen plasma treatment during a layer-by-layer direct spin-on process. Precise alignment of the features in each layer and a highly repeatable method are achieved by this new process. As a proof-of-concept, we successfully fabricated PDMS-based flexible microfluidic devices with SU-8-based rigid world-to-chip/chip-to-world interconnects. The bond strength between the PDMS and SU-8 layers is measured by three methods: (1) Instron® microtester to pull apart the layers; (2) voice coil actuator to test the bond between interconnects and the substrate; and (3) microfluidic pressurization test to evaluate the bond strength along the channels. The bond strength between the flexible PDMS layer and the rigid SU-8 features is very strong; the bond between these two polymers does not fail during these evaluations although the integrity of the PDMS layer itself fails during the microtester evaluation. Additionally, the layer-by-layer direct spin-on process resulted in a repeatable process and precise alignment of the features in each layer, which are necessary in order to achieve consistent performance from the fabricated devices. The rigid SU-8 interconnects fabricated onto a flexible PDMS device serve as a world-to-chip/chip-to-world interconnects for the direct connection with Tygon® tubing. Three different designs of hybrid (PDMS and SU-8 based) microfluidic devices are designed, fabricated and tested. Each variation differed in the microchannel design in order to demonstrate the versatility of the process to make devices on multiple scales and patterns. These hybrid microfluidic devices are capable of functioning without leakage up to pressures of 85.85 ±3.56 kPa. Although microfluidic channels with interconnects are shown as a proof-of-concept, the fabrication process demonstrated herein could be utilized to develop a number of more sophisticated microfluidic and biomedical devices.

Document type: 
Article
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Comprehensive Structural, Surface-Chemical and Electrochemical Characterization of Nickel-Based Metallic Foams

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-06-11
Abstract: 

Nickel-based metallic foams are commonly used in electrochemical energy storage devices (rechargeable batteries) as both current collectors and active mass support. These materials attract attention as tunable electrode materials because they are available in a range of chemical compositions, pore structures, pore sizes, and densities. This contribution presents structural, chemical, and electrochemical characterization of Ni-based metallic foams. Several materials and surface science techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), focused ion beam (FIB), and X-ray photoelectron spectroscopy (XPS)) and electrochemical methods (cyclic voltammetry (CV)) are used to examine the micro-, meso-, and nanoscopic structural characteristics, surface morphology, and surface-chemical composition of these materials. XPS combined with Ar-ion etching is employed to analyze the surface and near-surface chemical composition of the foams. The specific and electrochemically active surface areas (As, Aecsa) are determined using CV. Though the foams exhibit structural robustness typical of bulk materials, they have large As, in the range of 200–600 cm2 g–1. In addition, they are dual-porosity materials and possess both macro- and mesopores.

Document type: 
Article
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Colloidal Core–Shell Materials with ‘Spiky’ Surfaces Assembled From Gold Nanorods

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2014-05-14
Abstract: 

A series of core–shell materials with ‘spiky’ surfaces are prepared through the self-assembly of gold nanorods onto polystyrene microspheres. Loading of the nanorods is finely tuned and the assemblies exhibit surface plasmon resonance properties. The ‘spiky’ surface topography of the assembled structures could serve as a versatile substrate for surface-enhanced Raman spectroscopy based sensing applications.

Document type: 
Article
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Determining Adhesion of Non-Uniform Arrays of Fibrils

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2012-08-10
Abstract: 

Dry adhesives containing nonuniform arrays of fibrils were tested for the uniformity of their adhesion strength. These arrays comprised fibrils with nanometer-scale dimensions and lengths tuned from 150 to 1500 nm. The surfaces of the fibrils were rendered hydrophobic through a vapor phase deposition of silane molecules to further tune the adhesion strength of the fibrillar structure. Adhesion force measurements over micrometer-length scales were obtained using a tipless cantilever controlled by a scanning probe microscope. Maps of the adhesion forces depicted diverse variations in adhesion strength with the nonuniform lateral changes in topography. Through an extensive data analysis, differences observed between samples were correlated to changes in processing conditions and surface chemistry modifications. The methods demonstrated in this paper are useful for identifying variations in the adhesion strength of dry adhesives made of nonuniform arrays of fibrils. These advancements are crucial for understanding the correlation between structure and function within nonuniform fibrillar adhesives.

Document type: 
Article
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In situ X-ray Absorption Spectroscopic Studies of Magnetic Fe@FexOy/Pd Nanoparticle Catalysts for Hydrogenation Reactions

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-03-09
Abstract: 

Core@shell Fe@FexOy nano particles ( have attracted a great deal of interest as potential magnetic supports for catalytic metals via galvanic exchange reactions. In this study Fe@Fe x O y /Pd bimetallic NPs were synthesized through galvanic exchange reaction s using 50:1, 20:1 and 5:1 molar ratio s of Fe@Fe x O y NPs to Pd(NO 3 2 . The resulting Fe@Fe x O y /Pd NPs have Pd nanoparticles on the Fe ox ide surfaces, and the NPs are linked in chains as shown by TEM analysis and EDX mapping. After galvanic reactions with Pd , the particles still retain their response to external magnetic fields . The magnetic properties of the resulting materials led to the ir successful application as nanometer sized magnetic stir bars for hydrogenation reactions. The Fe@Fe x O y /Pd NPs derived f rom the 5:1 molar ratio of their respective salts (Fe:Pd) exhibit ed a higher catalytic activity than particles synthesized from 20:1 and 50:1 molar ratios for the hydrogenation of 2 methyl 3 buten 2 ol . T he highest turnover frequency reach ed 3600 h 1 using ethanol as a solvent. In situ X ray absorption near edge structure (XANES) spectra show that the Fe@Fe x O y core shell particles in the Fe@Fe x O y /Pd system are easily oxidized when dispersed in water, while they are very stable if ethanol is used as a solvent. This oxidative stability has important implications for the use of such particles in real world applications.

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Article
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Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-05-30
Abstract: 

Alcohol based monolayers were successfully formed on the surfaces of silicon oxides through reaction performed in polar aprotic solvents. Monolayers prepared from alcohol based reagents have been previously introduced as an alternative approach to covalently modify the surfaces of silicon oxides. These reagents are readily available, widely distributed, and are minimally susceptible to side reactions with ambient moisture. A limitation of using alcohol based compounds is that previous reactions required relatively high temperatures in neat solutions, which can degrade some alcohol compounds or could lead to other unwanted side reactions during the formation of the monolayers. To overcome these challenges, we investigate the condensation reaction for alcohols on silicon oxides carried out in polar aprotic solvents. In particular, propylene carbonate has been identified as a polar aprotic solvent that is relatively non-toxic, readily accessible, and can facilitate the formation of alcohol based monolayers. We have successfully demonstrated tuning the surface chemistry of silicon oxide surfaces with a variety of alcohol containing compounds. The strategy introduced in this research can be utilized to create silicon oxide surfaces with hydrophobic, oleophobic, or charged functionalities.

Document type: 
Article

Ordered Porous Electrodes by Design: Towards Enhancing the Effective Utilization of Platinum in Electrocatalysis

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-08-04
Abstract: 

Platinum‐nanoparticle‐functionalized, ordered, porous support electrodes are prepared and characterized as a potential new class of oxygen reduction reaction (ORR) electrocatalysts. This study aims to develop electrode materials that enhance the effective utilization of Pt in electrocatalytic reactions through improved mass transport properties, high Pt mass specific surface area, and increased Pt electrochemical stability. The electrodes are prepared using modular sacrificial templates, producing a uniform distribution of Pt nanoparticles inside ordered porous Au electrodes. This method can be further fine‐tuned to optimize the architecture for a range of characteristics, such as varying nanoparticle properties, pore size, or support material. The Pt‐coated Au, ordered, porous electrodes exhibit several improved characteristics, such as enhanced Pt effective utilization for ORR electrocatalysis. This includes a nearly twofold increase in Pt mass specific surface area over other ultrathin designs, superior mass transport properties in comparison to traditional catalyst layers of C black supported Pt nanoparticles mixed with ionomer, good methanol tolerance and exceptional stability toward Pt chemical and/or electrochemical dissolution through interfacial interactions with Au. The methods to prepare Pt‐coated ordered porous electrodes can be extended to other architectures for enhanced catalyst utilization and improved performance of Pt in electrochemical processes.

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Article
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Surfactant Controlled Growth of Niobium Oxide Nanorods

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-08-14
Abstract: 

his paper describes a solution-phase hydrothermal synthesis of crystalline niobium pentoxide (Nb2O5) nanorods. The methods reported herein yield uniform Nb2O5 nanorods with average diameters of 6 nm and lengths of 38 nm, which are directly synthesized from niobic acid by a hydrothermal process. The formation of Nb2O5 nanorods from niobic acid was studied in the presence of surfactants that stabilize the nanostructures. The crystalline Nb2O5 nanorods were relatively uniform in size and shape. The size of the Nb2O5 nanorods could be tuned through the choice of surfactant even in the absence of a worm-like micellar morphology. Amine, amide, ammonium, carboxylate, sulfonate, and sulfate containing surfactants were systematically evaluated for their influence on the ability to form uniform Nb2O5 nanorods. The surfactants in this study had hydrophobic tails that were either straight or branched, such as a polymer, and contained either a single or multiple head groups. The nanorods grew by a process of oriented attachment of nanoparticles that was regulated by the surfactants added into the reaction mixture. The results of these studies indicate that this synthetic approach serves as a tunable platform to prepare single crystalline niobium oxide based nanostructures with well-defined morphologies and dimensions. This surfactant assisted formation of crystalline Nb2O5 nanorods could also have important implications in the design of other transition metal oxide based nanomaterials.

Document type: 
Article