Enhancement of service life of polymer electrolyte fuel cells through application of nanodispersed ionomer

Copyright © 2020 The Authors, some rights reserved.In polymer electrolyte fuel cells (PEFCs), protons from the anode are transferred to the cathode through the ionomer membrane. By impregnating the ionomer into the electrodes, proton pathways are extended and high proton transfer efficiency can be achieved. Because the impregnated ionomer mechanically binds the catalysts within the electrode, the ionomer is also called a binder. To yield good electrochemical performance, the binder should be homogeneously dispersed in the electrode and maintain stable interfaces with other catalyst components and the membrane. However, conventional binder materials do not have good dispersion properties. In this study, a facile approach based on using a supercritical fluid is introduced to prepare a homogeneous nanoscale dispersion of the binder material in aqueous alcohol. The prepared binder exhibited high dispersion characteristics, crystallinity, and proton conductivity. High performance and durability were confirmed when the binder material was applied to a PEFC cathode electrode11sciescopu

Effects of ionomer content on Pt catalyst/ordered mesoporous carbon support in polymer electrolyte membrane fuel cells

In this paper, the optimum Nafion ionomer content in platinum (Pt) dispersed on ordered mesoporous carbon (OMC) catalyst is investigated. The ionomer content can affect catalytic activity, ionic conductivity and mass transfer characteristics. A nano-replication method using ordered mesoporous silicas (OMS) is applied to prepare OMCs, and Pt/OMC with high loading are synthesized by the incipient wetness method for polymer electrolyte membrane fuel cells (PEMFCs). Catalyst characteristics have been analyzed using TGA, XRD, TEM and BET. Cathode electrodes have different ionomer loadings (in the range of 5-30 wt. %) with Pt/OMCs. Commercial Pt/C catalyst is used in anode. All membrane electrode assemblies (MEAs) fabricated by the decal transfer method show about 0.4 mg cm(-2) Pt loading. The PEMFC performances have been measured by electrochemical methods such as polarization curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The performances is different at low and high current density regions, and the optimum content of ionomer is 10 wt. % in the catalyst, due to unique structure of OMCs.close7

Effect of different surface functional groups on carbon supports toward methanol electro-oxidation of Pt nanoparticles

With an increased demand for efficient energy conversion system, nanoscale electrocatalysts have been intensively studied for high activity and stability. However, carbon support for nanoparticulate electrocatalyst has been generally thought to be inert for reaction pathway on metal nanocrystals. Therefore, material design for carbon support has mainly focused on development of high surface area with engineered pore structure, while surface state of the support has been largely neglected. Here, we demonstrate that surface functionalization of carbon support can modulate catalytic performance of Pt nanoparticle towardmethanol electro-oxidation. Vulcan carbon (VC) surface was successfully modified by either acid oxidation or urea annealing, resulting in oxygen-rich (O-VC) and nitrogen-rich (N-VC) surface states, respectively. Modified surface state of carbon supports were investigated with XPS spectra. With controlled experiments, uniform Pt nanoparticles (d similar to 5 nm) were deposited on each carbon support for the same electrochemical surface area. Through high-resolution XPS analysis, electronic transfer from nitrogen to Pt was monitored in Pt/N-VC. With electron-enriched surface, Pt/N-VC reveals less oxophilic surface property compared to Pt/VC and Pt/O-VC. Notably, methanol electro-oxidation reaction largely depended on types of functional groups. Compared to Pt/VC, methanol oxidation decreased 30% in oxygen-rich Pt/O-VC after surface oxidation, while reaction rate increased double in nitrogen-rich Pt/N-VC. From CO bulk oxidation result, improved MOR activity of Pt/N-VC is attributed to larger number of available Pt active sites from attenuated adsorption of oxygen species. Therefore, this study highlights the importance of surface engineering in carbon supports for electrocatalysis.11Nsciescopu

Origami-Based Flexible and Simple Tubular Polymer Electrolyte Membrane Fuel Cell Stack

© 2021 American Chemical Society.Flexible energy devices are essential for future small and flexible devices, and there are many challenges to create deformable energy devices. In this study, we developed a lightweight and flexible passive air-breathing polymer electrolyte membrane fuel cell (PEMFC) stack with a flexible 3D structure using a straw-like tubular design. This stack is lighter than a conventional PEMFC stack because it contains a smaller number of components. By applying a conical design, the device was easily assembled with the units connected in series using banded-type connections (i.e., without clamps or fixing parts). Moreover, for the first time, a conical reverse truss origami design was applied to the tubular PEMFC, which enabled 3D movement and reduced the volume of the PEMFC. The flexible tubular PEMFC is expected to be an energy source for small devices and can be used to replace wires or external fuel pipelines in devices that require mechanical movement.11Nsciescopu

Improved electrochemical performance of a three-dimensionally ordered mesoporous carbon based lithium ion battery using vinylene carbonate

The effects of vinylene carbonate (VC) as an electrolyte additive on a 3-dimensionally ordered mesoporous carbon based lithium ion battery are investigated. Our investigation reveals an optimal concentration of VC, which improves the discharge specific capacity at the 100th cycle to 844.3 from 684.3mAhg-1, and improves the first cycle's coulombic efficiency to 32.4 from 23.7%. The improvements are revealed to be a result of reduced charge transfer and solid electrolyte interface resistance, enabling better permeability of Li ions. This work demonstrates that VC is a viable electrolyte additive in improving the performance of a non-graphitic carbonaceous material. © 2015 Elsevier Ltd1331scopu

Guided cracking of electrodes by stretching prism-patterned membrane electrode assemblies for high-performance fuel cells

Guided cracks were successfully generated in an electrode using the concentrated surface stress of a prism-patterned Nafion membrane. An electrode with guided cracks was formed by stretching the catalyst-coated Nafion membrane. The morphological features of the stretched membrane electrode assembly (MEA) were investigated with respect to variation in the prism pattern dimension (prism pitches of 20 μm and 50 μm) and applied strain (S ≈ 0.5 and 1.0). The behaviour of water on the surface of the cracked electrode was examined using environmental scanning electron microscopy. Guided cracks in the electrode layer were shown to be efficient water reservoirs and liquid water passages. The MEAs with and without guided cracks were incorporated into fuel cells, and electrochemical measurements were conducted. As expected, all MEAs with guided cracks exhibited better performance than conventional MEAs, mainly because of the improved water transport. © 2018 The Author(s)1

Biomass waste, coffee grounds-derived carbon for lithium storage

Biomass waste-derived carbon is an attractive alternative with environmental benignity to obtain carbon material. In this study, we prepare carbon from coffee grounds as a biomass precursor using a simple, inexpensive, and environmentally friendly method through physical activation using only steam. The coffee-derived carbon, having a micropore-rich structure and a low extent of graphitization of disordered carbon, is developed and directly applied to lithium-ion battery anode material. Compared with the introduction of the Ketjenblack (KB) conducting agent (i.e., coffee-derived carbon with KB), the coffee-derived carbon itself achieves a reversible capacity of ~200 mAh/g (0.54 lithium per 6 carbons) at a current density of 100 mA/g after 100 cycles, along with excellent cycle stability. The origin of highly reversible lithium storage is attributed to the consistent diffusion-controlled intercalation/de-intercalation reaction in cycle life, which suggests that the bulk diffusion of lithium is favorable in the coffee-derived carbon itself, in the absence of a conducting agent. This study presents the preparation of carbon material through physical activation without the use of chemical activation agents and demonstrates an application of coffee-derived carbon in energy storage devices. (c) 2018, Korean Electrochemical Society. All rights reserve

Discharging a Li-S battery with ultra-high sulphur content cathode using a redox mediator

Lithium-sulphur batteries are under intense research due to the high specific capacity and low cost. However, several problems limit their commercialization. One of them is the insulating nature of sulphur, which necessitates a large amount of conductive agent and binder in the cathode, reducing the effective sulphur load as well as the energy density. Here we introduce a redox mediator, cobaltocene, which acts as an electron transfer agent between the conductive surface and the polysulphides in the electrolyte. We confirmed that cobaltocene could effectively convert polysulphides to Li 2 S using scanning electron microscope, X-ray absorption near-edge structure and in-situ X-ray diffraction studies. This redox mediator enabled excellent electrochemical performance in a cathode with ultra-high sulphur content (80 wt%). It delivered 400 mAh g -1 cathode capacity after 50 cycles, which is equivalent to 800 mAh g -1 S in a typical cathode with 50 wt% sulphur. Furthermore, the volumetric capacity was also dramatically improved. © The Author(s) 20161561sciescopu

Structural modification of electrode for anion exchange membrane fuel cell by controlling ionomer dispersion

An appropriate electrode microstructure design should be necessary to achieve high-performance anion exchange membrane fuel cells (AEMFCs). In general, the electrodes are fabricated from catalyst slurries which contain self-assembled agglomerates of catalyst particles with ionomer dispersed in a solvent. Therefore, solvent nature greatly affects the microstructure of the electrode, such as the pore structure and the formation of triple-phase boundaries for electrochemical reactions. Here, we investigate the influence of solvent on the microstructure of I2 ionomer-based electrode and its performance using three alcohol-based solvents (ethanol, 2-propanol, and 2-methyl-2-propanol [tBuOH)) with different dielectric constants and similar boiling points. Various physical and electrochemical characterization confirmed that the electrode pore structure changes significantly depending on the type of solvent while the electrochemically active surface area hardly changes. Furthermore, the efect of the three electrodes with different pore structures on AEMFC performance is observed for anode and cathode, respectively. It is demonstrated that the porous electrode with large pores is more advantageous in performance than a dense electrode at both the anode and the cathode for AEMFC. Consequently, the membrane electrode assembly with porous tBuOH-based electrodes exhibits more than 40% higher performance (1.32 W cm(-2)) than dense ethanol-based electrodes (0.94 W cm(-2)).11Nsciescopu