Novel Polymer Electrolyte Nano-Composite Membranes for Fuel Cell Applications

Fuel cells are electrochemical devices which have been established to lead in the transition to clean energy technology and will become the energy efficient power source of the future. Among all the fuel cell systems, anion exchange membrane fuel cells (AEMFCs) and solid polymer electrolyte membrane fuel cells (PEMFCs) are qualified of achieving high power densities (>l W cm-2) that is required for many applications. Mainly, operation of AEMFCs and PEMFCs at higher temperatures (100-130 °C) would considerably enhance their kinetic performance over the current lower temperature operation technologies. However, due to the type of materials used in each fuel cell there is an associated set of challenges including cost and lifetime which require innovative engineering solutions. One of the important challenges is the fabrication of a cost effective solid electrolyte with high efficiency and durability for both PEMFCs and AEMFCs. Concerning PEMFCs, the state of the art perfluorosulfonic acid (PFSA) membrane (Dupont Nafion®) has high ionic conductivity and good mechanical and chemical stability. However, its high performance and durability is limited to the operational conditions (e.g., temperature, humidity, and pH). In the case of AEMFCs, the dilemma between high ionic conductivity and physicochemical stability for membranes is an important issue, i.e., maximizing one will minimize the other. Thus, for both PEMFCs and AEMFCs, there is a desire to develop a solid electrolyte material capable of maintaining both ion-conductivity and durability at the same time for various operational conditions, especially elevated temperature conditions. The main goal of this research project has been the design and fabrication of novel nano-composite electrolyte membranes that fulfills all the aforementioned requirements for a cost effective solid electrolyte membrane in both PEMFCs and AEMFCs. To accomplish this, different approaches have been effectively integrated and improved by understanding and combination of organic chemistry, electrochemistry, chemical engineering and nano-materials science. Hygroscopic nano-fillers made of titanium oxide nanotubes (TiO2-NT) or graphene oxide (GO) nanosheets were first functionalized with highly ion-conductive groups, and then composed with the commercial membrane or another type of polymeric backbone. The latter was morphologically modified to favor higher electrolyte and water absorption capacity. Combining the benefits of a nano-filler with a morphologically modified polymer electrolyte effectively led to the development of a highly ion-conductive, water-retentive, and durable electrolyte membrane. Electrochemical, thermal, physical and chemical properties of proposed membranes were tested, analyzed and reported by various characterization methods. For PEMFC applications, the developed nano-composite PFSA membranes demonstrated significant ion conductivity and single fuel cell performance improvement (~4 times) over commercial PEM at the humidity of 30 % and temperature of 120 °C. For AEMFCs, the selected nano-filler (e.g., GO) composed with morphologically modified polymer (e.g., porous polybenzimidazole) notably increased both performance and durability of AEMs in harsh alkaline conditions. This work offered promising solid electrolyte replacements synthesized by simple and cost effective techniques, able to meet the fuel cell market demands.4 month

Plasmon-free polymeric nanowrinkled substrates for surface-enhanced raman spectroscopy of two-dimensional materials

We report plasmon-free polymeric nanowrinkled substrates for surface-enhanced Raman spectroscopy (SERS). Our simple, rapid, and cost-effective fabrication method involves depositing a poly(ethylene glycol)diacrylate (PEGDA) prepolymer solution droplet on a fully polymerized, flat PEGDA substrate, followed by drying the droplet at room conditions and plasma treatment, which polymerizes the deposited layer. The thin polymer layer buckles under axial stress during plasma treatment due to its different mechanical properties from the underlying soft substrate, creating hierarchical wrinkled patterns. We demonstrate the variation of the wrinkling wavelength with the drying polymer molecular weight and concentration (direct relations are observed). A transition between micron to nanosized wrinkles is observed at 5 v % concentration of the lower molecular-weight polymer solution (PEGDA Mn 250). The wrinkled substrates are observed to be reproducible, stable (at room conditions), and, especially, homogeneous at and below the transition regime, where nanowrinkles dominate, making them suitable candidates for SERS. As a proof-of-concept, the enhanced SERS performance of micro/nanowrinkled surfaces in detecting graphene and hexagonal boron nitride (h-BN) is illustrated. Compared to the SiO2/Si surfaces, the wrinkled PEGDA substrates significantly enhanced the signature Raman band intensities of graphene and h-BN by a factor of 8 and 50, respectively

Effects of Diffusive Charge Transfer and Salt Concentration Gradient in Electrolyte on Li-ion Battery Energy and Power Densities

The simulation of lithium-ion batteries based on a fundamental multi-physicochemical model requires extensive computational resources and remains sluggish for real-time or battery pack analysis applications. In these applications, simplification of the model is required to reduce computational costs while maintaining the model accuracy in estimation of one or more performance parameters. In this study, the effects of neglecting the lithium-ion diffusive charge transfer and the salt concentration gradient in electrolyte on the model accuracy are investigated. The results indicate the feasibility of simplifying the model for a range of cell designs and discharge rates without sacrificing the preciseness of the cell energy and power density predictions

Plasmon-free polymeric nanowrinkled substrates for surface-enhanced Raman spectroscopy of two-dimensional materials

We report plasmon-free polymeric nanowrinkled substrates for surface-enhanced Raman spectroscopy (SERS). Our simple, rapid and cost-effective fabrication method involves depositing a poly(ethylene glycol) diacrylate (PEGDA) prepolymer solution droplet on a fully polymerized, flat PEGDA substrate, followed by drying the droplet at room conditions and plasma treatment, which polymerizes the deposited layer. The thin polymer layer buckles under axial stress during plasma treatment due to its different mechanical properties from the underlying soft substrate, creating hierarchical wrinkled patterns. We demonstrate the variation of the wrinkling wavelength with the drying polymer molecular weight and concentration (direct relations are observed). A transition between micron to nanosized wrinkles is observed at 5 v% concentration of the lower molecular weight polymer solution (PEGDA Mn 250). The wrinkled substrates are observed to be reproducible, stable (at room conditions) and, specially, homogeneous at and below the transition regime, where nanowrinkles dominate, making them suitable candidates for SERS. As a proof-of-concept, the enhanced SERS performance of micro/nano-wrinkled surfaces in detecting graphene and hexagonal boron nitride (h-BN) is illustrated. Compared to the SiO2/Si surfaces, the wrinkled PEGDA substrates significantly enhanced the signature Raman bands intensities of graphene and h-BN by a factor of 8 and 50, respectively. </p

Molecular Functionalization of Graphene Oxide for Next-Generation Wearable Electronics

Acquiring reliable and efficient wearable electronics requires the development of flexible electrolyte membranes (EMs) for energy storage systems with high performance and minimum dependency on the operating conditions. Herein, a freestanding graphene oxide (GO) EM is functionalized with 1-hexyl-3-methyl­imidazolium chloride (HMIM) molecules via both covalent and noncovalent bonds induced by esterification reactions and electrostatic π_cation–π stacking, respectively. Compared to the commercial polymeric membrane, the thin HMIM/GO membrane demonstrates not only slightest performance sensitivity to the operating conditions but also a superior hydroxide conductivity of 0.064 ± 0.0021 S cm^–1 at 30% RH and room temperature, which was 3.8 times higher than that of the commercial membrane at the same conditions. To study the practical application of the HMIM/GO membranes in wearable electronics, a fully solid-state, thin, flexible zinc–air battery and supercapacitor are made exhibiting high battery performance and capacitance at low humidified and room temperature environment, respectively, favored by the bonded HMIM molecules on the surface of GO nanosheets. The results of this study disclose the strong potential of manipulating the chemical structure of GO to work as a lightweight membrane in wearable energy storage devices, possessing highly stable performance at different operating conditions, especially at low relative humidity and room temperature