Jacob S. Spendelow

Morphology-dependent performance of CuO anodes via facile and controllable synthesis for lithium-ion batteries.

Nanostructured CuO anode materials with controllable morphologies have been successfully synthesized via a facile and environmentally friendly approach in the absence of any toxic surfactants or templates. In particular, leaf-like CuO, oatmeal-like CuO, and hollow-spherical CuO were obtained by changing the ligand agents. The structures and electrochemical performance of these as-prepared CuO were fully characterized by various techniques, and the properties were found to be strongly dependent on morphology. As anode materials for lithium-ion batteries, the leaf-like CuO and oatmeal-like CuO electrodes exhibit relatively high reversible capacities, whereas hollow-spherical CuO shows enhanced reversible capacity after initial degradation. Furthermore, an excellent high rate capability was obtained for the leaf-like CuO and hollow-spherical CuO electrodes. These results may provide valuable insights for the development of nanostructured anodes for next-generation high-performance lithium-ion batteries.

Air-Breathing Laminar Flow-Based Direct Methanol Fuel Cell with Alkaline Electrolyte

Microfuel cells have the potential to achieve higher energy densities than batteries and have thus received intense investigation as a power source for a wide range of portable applications. Extensive research efforts are focused on the development and miniaturization of promising fuel cell technologies, including direct methanol fuel cells DMFCs and polymer electrolyte membrane-based fuel cells PEMFCs, operated with hydrogen/oxygen. 1-3 In most fuel cells, a polymer electrolyte membrane such as Nafion allows protons to diffuse from the anode to the cathode, while trying to prevent fuel molecules from diffusing across and mixing with oxygen at the cathode. Poor performance or a lack of selectivity by the membrane leads to a key performance-limiting process called fuel crossover that has plagued the PEM-based fuel cells. In addition to fuel crossover, cathode flooding and anode dry-out water management due to osmotic drag of water molecules associated with protons diffusing from the anode to the cathode, as well as due to the formation and consumption of water at the cathode and anode, respectively, impedes the performance and commercial implementation of these fuel cells. 4

Graphene/Fe2O3/SnO2 Ternary Nanocomposites as a High-Performance Anode for Lithium Ion Batteries

We report an rGO/Fe2O3/SnO2 ternary nanocomposite synthesized via homogeneous precipitation of Fe2O3 nanoparticles onto graphene oxide (GO) followed by reduction of GO with SnCl2. The reduction mechanism of GO with SnCl2 and the effects of reduction temperature and time were examined. Accompanying the reduction of GO, particles of SnO2 were deposited on the GO surface. In the graphene nanocomposite, Fe2O3 nanoparticles with a size of ∼20 nm were uniformly dispersed surrounded by SnO2 nanoparticles, as demonstrated by transmission electron microscopy analysis. Due to the different lithium insertion/extraction potentials, the major role of SnO2 nanoparticles is to prevent aggregation of Fe2O3 during the cycling. Graphene can serve as a matrix for Li+ and electron transport and is capable of relieving the stress that would otherwise accumulate in the Fe2O3 nanoparticles during Li uptake/release. In turn, the dispersion of nanoparticles on graphene can mitigate the restacking of graphene sheets. As a result, the electrochemical performance of rGO/Fe2O3/SnO2 ternary nanocomposite as an anode in Li ion batteries is significantly improved, showing high initial discharge and charge capacities of 1179 and 746 mAhg(-1), respectively. Importantly, nearly 100% discharge-charge efficiency is maintained during the subsequent 100 cycles with a specific capacity above 700 mAhg(-1).

Noble metal decoration of single crystal platinum surfaces to create well-defined bimetallic electrocatalysts

Electrocatalytic studies on bimetallic single crystal electrodes present a unique opportunity to explore the reactivity of complex surfaces with known structure and composition. Such electrochemical studies, together with measurements in ultra-high vacuum, provide the theoretical and experimental basis for rational design of more active electrocatalysts. Pure platinum, though the most active single-component electrocatalyst for many reactions, is still not active enough for some applications, particularly in fuel cell technology, and cannot be considered as a true catalyst for most electrocatalytic processes. Therefore, a concerted effort has been made in the last 40 years to enhance the electrocatalytic activity of Pt via modification by a second metal. Most early work used polycrystalline alloys, but in recent years, many workers have begun modifying (decorating) Pt single crystals by deposition of a second noble metal, which is usually ruthenium, palladium, rhodium, osmium, or silver. A critical review of electrocatalysis on such well-defined bimetallic surfaces is offered, and a brief analysis of the inverted approach, in which single crystal noble metal surfaces are modified by Pt deposition, is also presented.

The Role of Surface Defects in CO Oxidation, Methanol Oxidation, and Oxygen Reduction on Pt ( 111 )

Some surface reactions of interest to electrocatalysis in alkaline media are promoted by crystalline defects, while others occur preferentially on defect-free terraces. Different forms of structure sensitivity, and the underlying causes of this structure sensitivity, have been examined using several fuel-cell-relevant surface reactions in alkaline media as model reactions. Oxidation of CO serves as a model for defect favored reactions, while reduction of oxygen serves as a model for terrace favored reactions. More complicated reactions, such as methanol oxidation, can be interpreted as containing multiple steps that are either defect favored or terrace favored. The role of defects in each of these reactions was interpreted in terms of geometric and electronic effects, with different types of defects kink type and step type showing different effects for the different electrocatalytic processes. CO oxidation is promoted by both step-type and kink-type defects, as a result of electronic structure, but methanol dehydrogenation is promoted only by step-type defects, as a result of geometric structure.

Imaging of Water Profiles in PEM Fuel Cells Using Neutron Radiography: Effect of Operating Conditions and GDL Composition

The performance of polymer electrolyte membrane (PEM) fuel cells as a function of cathode inlet relative humidity (RH) and gas diffusion layer (GDL) properties has been characterized. The performance of 50 cm2 fuel cells at high current densities was a strong function of the polytetrafluoroethylene (PTFE) content in the cathode GDL microporous layer (MPL). The voltage at a current density of 1.4 A cm-2 decreased at all inlet RHs as the PTFE content in the cathode MPL increased from 5 % by weight to 23 % by weight. This was associated with a corresponding increase in the mass transport resistance as measured by AC impedance. The low frequency resistance also increased with increasing cathode inlet RH. These results were validated by high-resolution neutron radiography on specially designed 2.25 cm2 cells that showed increased water content in the GDLs at high inlet RHs and high microporous layer PTFE content. High-resolution neutron imaging also revealed higher water concentrations at the outlets, cathode GDL, anode flow channel, and MEA/GDL above the land when compared to the inlets, anode GDL, cathode flow channel, and MEA/GDL above the channel respectively.

Nitrogen‐Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm-2 ). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates.

Ice Formation in PEM Fuel Cells Operated Isothermally at Sub-Freezing Temperatures

The durability of polymer electrolyte membrane (PEM) fuel cells operated at sub-freezing temperatures has received increasing attention in recent years. 1 The Department of Energy’s PEM fuel cell stack technical targets for the year 2010 include un-assisted startup from –40 o C and startup from -20 o C ambient in as low as 30 seconds with < 5MJ energy consumption. Moreover, the sub-freezing operations should not have any impact on achieving the other technical targets including 5000 hours durability. We have previously characterized the performance of both cloth (E-tek) and paper (SGL) GDLs and reported that the paper GDLs show lower tolerance to sub-freezing temperatures. 2 We have also reported the performance of MEAs at -10 o C where ice formation results in mass transport limitations. 3 Finally we reported on the effect of MEA preparation on durability and also provided low resolution neutron imaging data to identify ice formation in the land/channel areas. 4 In this paper we report the effect of MEA/GDL structure and cell assembly on sub-freezing performance. We also present highresolution neutron radiographs of single cells operated at sub-freezing temperatures to identify the exact location of ice formation and its effect on durability.

Effect of Hydrophilic Treatment of Microporous Layer on Fuel Cell Performance

The gas diffusion layer in a polymer electrolyte fuel cell is the component primarily responsible for effective water management under a wide variety of conditions. The incorporation of hydrophilic alumosilicate fibers in the microporous layer leads to an improvement in the fuel cell performance associated with a decrease in the mass transport resistance especially under high RH operation. This improvement in performance is obtained without sacrificing performance under low RH conditions. The alumosilicate fibers create domains that wick liquid water away from the catalyst layer. The improved mass transport performance is corroborated by AC impedance and neutron radiography analysis and is consistent with an increase in the average pore diameter inside the microporous layer.

Self-Assembled Reduced Graphene Oxide/Polyacrylamide Conductive Composite Films

Substrate supported conductive thin films are prepared by the self-assembly of graphene oxide (GO) on a cationic polyacrylamide (CPAM) layer followed by a subsequent chemical reduction. During self-assembly, the dispersed GO nanosheets with a negative zeta potential from solution are spontaneously assembled onto the positively charged CPAM adsorption layer. In addition, CPAM adsorption on the substrate is studied with an electrochemical quartz crystal microbalance (EQCM), showing adsorption stabilization could be established in less than 150 s. The electrostatic interactions between GO and CPAM are investigated by changing the polarization potential with EQCM for the first time, and optimal conditions for facilitating self-assembly are determined. The self-assembled GO/CPAM films are further characterized by Raman spectroscopy, infrared spectroscopy and atomic force microscopy. Importantly, reduced GO (R-GO)/CPAM composite films exhibiting a sheet resistance of 3.1 kΩ/sq can be obtained via in situ reduction in sodium borohydride for 20 min at room temperature. This provides a simple, highly effective, and green route to prepare conductive graphene-based composite thin films.