Special Issue "Membranes for Electrochemical Energy Applications"

Guest Editor
Prof. Dr. Bruno Scrosati
Department of Chemistry, University Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy
Website: http://www.chem.uniroma1.it/persone/bruno-scrosati
E-Mail: bruno.scrosati@gmail.com
Phone: +39 06 4991 3530
Fax: +39 06 4462 866
Interests: polymer electrolyte membrane fuel cells; lithium polymer batteries

Dear Colleagues,

Membranes play a key role in energy-related fields since they are the main components of devices which could help address one of the most serious threats to our society, namely global warming. Serious concern is associated with the continuous CO₂ emission resulting from our energy policy, which is still mainly based on burning of fossil fuels. Accordingly, an efficient use of renewable energy sources and the replacement of internal combustion engines with electric motors for the development of sustainable vehicles, such as hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs) and ultimately, full electric vehicles (EVs), are major goals in the present energy scenario. On the other hand, an efficient use of alternative, green, energy sources, such as solar and wind, requires the side support of energy storage systems that can compensate for their intermittent characteristics. Analogously, HEVs, PHEVs and EVs require an on-board energy source for powering the electric engine. Among the various choices, electrochemical devices, such as fuel cells and batteries, capable of delivering stored chemical energy as electrical energy with high conversion efficiency and without any gaseous emission, are the most suitable. Moreover, fuel cells and batteries offer a promising option to efficiently power the electric engine in HEVs or EVs.

The most common and most studied fuel cells utilize a perfluorosulfonic membrane electrolyte, mainly of the NAFION^® type. Although becoming increasingly well-known over time, these membranes still require attention to further improve performance. Much research is presently being carried out in this area, and this Special Issue will be a perfect forum to bring together the latest results obtained by key laboratories presently engaged in polymer electrolyte membrane fuel cell R&D.

In terms of battery research, particular interest is focused on lithium batteries due to their intrinsic, high energy density value. However, in their present configuration, lithium batteries are affected by a series of issues that still prevent their wide use for electric vehicle application. One of the most serious is the safety concern associated with the unstable and flammable nature of the common liquid electrolytes. Improving safety is thus a present challenge in the field. One approach to reach this goal is to move away from the unreliable liquid, organic electrolytes, to stable and safe polymer electrolyte membranes. There are two classes of these membranes: a polymer-liquid hybrid type, generally named gel-type membranes, and membranes formed by liquid-free combinations of polymer with lithium salts, generally named solid polymer electrolytes. Today there is tremendous research ongoing worldwide is involved into lithium batteries, motivated by a large amount of funding granted in many countries. Therefore, breakthroughs in the area―especially in membrane electrolyte and related polymer batteries―are expected to soon concretize. Again, this Special Issue offers a perfect site for welcoming the latest innovations, and accordingly authors from top laboratories are invited to submit their latest results.

Prof. Dr. Bruno Scrosati
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Membranes is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. For the first couple of issues the Article Processing Charge (APC) will be waived for well-prepared manuscripts. English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

• hydrogen conducting membranes
• perfluorosulfonic membranes
• fuel cells
• lithium conducting membranes
• gel-type membranes
• solvent-free, solid-state membranes
• lithium batteries

Title: U.S. DOE Progress Towards Developing Low-Cost, High Performance, Durable Polymer Electrolyte Membranes for Fuel Cell Applications
Authors: C. Houchins ¹; G. J. Kleen ²; J. S. Spendelow ³; D. Peterson ²; N. L. Garland ²; D. L. Ho ²; J. Marcinkoski ²;  K. E. Martin ²; R. Tyler ² and D. C. Papageorgopoulos ²
Affiliations: ¹ SRA International, Fairfax, VA 22033, USA
² U.S. Department of Energy, Washington, DC 20585, USA; E-Mail: Dimitrios.Papageorgopoulos@ee.doe.gov
³ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Abstract: Low cost, durable, and selective membranes with high ionic conductivity are a high priority need for wide-spread adoption of fuel cells. In polymer electrolyte membrane fuel cells (PEMFCs), the membrane is a major cost component of the fuel cell stack at low production volumes. PEMFC membranes also impose limitations on fuel cell system operating conditions that add system complexity and cost, while mechanical stress and chemical degradation can cause membrane failure. Reactant gas permeation through the membrane leads to decreased fuel cell performance, loss of efficiency, and reduced durability. To address these challenges, the U.S. Department of Energy (DOE) Fuel Cell Technologies Program in the Office of Energy Efficiency and Renewable Energy supports research and development projects aimed at improving ion exchange membranes for fuel cells. In this paper, the recently revised DOE membrane targets and highlights of DOE-supported projects to develop new membrane materials will be discussed. The focus is on developing inexpensive membranes that have good performance in hot and dry conditions. Strategies that have been investigated in DOE-supported projects include: membranes based on heteropolyacid proton conductors, rigid rod polymer membranes with increased conductivity, dual nanofiber electrospun and dimensionally stabilized composite membranes with decreased swelling and increased durability, new multi-acid side chain polymers, and DMFC membranes with reduced methanol crossover. Recent activities and progress from these research and development efforts will be discussed.

Title: Microscopic Analysis of Current and Mechanical Properties at Nafion^® by Studied AFM
Authors: Renate Hiesgen ¹, Stefan Helmly ^1,2, Ines Galm ¹, Tobias Morawietz ¹, Michael Handl ¹ and K. Andreas Friedrich ²
Affiliations: ¹ University of Applied Sciences Esslingen Kanalstrasse 33, Esslingen 73728, Germany
² German Aerospace Center, Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, Stuttgart 70569, Germany; E-Mail: renate.hiesgen@hs-esslingen.de
Abstract: One of the challenges in the further development of membranes for polymer-electrolyte fuel cells is to ascertain a high and homogeneous ionic conductivity. In proton-conducting membranes water transport and conductivity are closely connected by the electro osmotic drag. Characterization of the conductivity of different fuel cell membranes at the nanometer scale has been performed by advanced tapping mode atomic force microscopy techniques, the so-called PeakForce QNM^© and PeakForce TUNA^© (Bruker Corp.). The conductivity of different types of solid electrolyte membranes as well as their mechanical properties has been analysed. AFM yields high resolution images of the conductive structure at membrane surfaces and some insight into the bulk conducting network. The correlation of conductivity with other mechanical properties like i.e., adhesion force, deformation, and stiffness, simultaneously measured with the current, gives an indication of subsurface phase separations and phase distribution at the surface of the membrane. In more detail, subsurface regions containing water can be discerned from dry subsurface volume. The distribution of conductive pores at the surface can clearly be identified by water droplet formation.

Title: Polymer Electrolyte Membranes in Electrochemical Separation Processes
Authors: T. Vidakovic-Koch ¹; I. Gonzalez Martinez ²; L. Rihko-Struckmann ¹; C. Oettel ¹ and K. Sundmacher ^1,2
Affiliations: ¹ Max Planck Institute for Dynamics of Complex Technical Systems, Process Systems Engineering, Sandtorstrasse 1, 39106 Magdeburg, Germany
² Otto von Guericke University, Process Systems Engineering, Universitätsplatz 2, 39106 Magdeburg, Germany
Abstract: Polymer electrolyte membranes have found a broad application in number of processes, being fuel cells due to energy concerns lately, the focus of the scientific community worldwide. Relatively less attention is paid to the use of these materials in electrochemical production and separation processes. In this mini-review we put emphasis on the application of polymer electrolyte membranes, Nafion and polybenzimidazoles (PBI), in electrochemical membrane reactors for production and separation of two important bulk chemicals, chlorine and hydrogen respectively. The performance of such an electrochemical reactor is influenced by a number of factors, whereby the membrane properties play an important role in reactor optimization. The review focuses on the performances of such electrochemical membrane reactors underlining some important challenges like humidification (acid doping), gas crossover, corrosion, and long term stability.

Title: A Caesium-Salts-of Heteropolyacids/Quaternary Diazabicyclo-Octane Polysulfone/Poly(tetrafluoroethylene) Composites Membrane for Intermediate Temperature Fuel Cells
Authors: Chenxi Xu, Xu Wang, Wu Xu, Yuancheng Cao and Keith Scott
Affiliation: School of Chemical Engineering & Advanced Materials, Newcastle University, Newcastle NE1 7RU, UK; E-Mail: k.scott@ncl.ac.uk (K.S.)
Abstract: Inorganic–organic composite electrolyte membranes were fabricated from CsPOMo and quaternary diazabicyclo-octane polysulfone with Polytetrafluoroethylene (QDPSU/PTFE) for application in intermediate temperature (100–200 °C) hydrogen fuel cells. Comparing to nafion® electrolyte. A higher operating temperature would enhance the thermodynamic efficiency and kinetics of the system thus provided possibility to use non-noble metal as catalyst. Good mechanical strength provided from PTFE is also an optimising property for membrane, which will benefit the working period in the fuel cells. The Cs_XH_3−XPMo₁₂O₄₀ (CsPOMo)/QDPSU/PTFE composite membrane was prepared with low phosphoric acid loading to increase the membrane proton conductivity and mechanical strength. Several fabrication techniques (e.g., casting, membrane doping) were used in order to build a thin and robust composite membrane. The resulting membrane materials were characterised in terms of composition, structure and morphology by EDX, FTIR and SEM. The proton conductivity and fuel cell performance were 0.04 Scm⁻¹ and 240 mW cm⁻², respectively.

Title: UV-curable Polymer Electrolyte Membranes for Li-based Battery Application
Authors: Jijeesh R. Nair, Annalisa Chiappone, Juqin Zeng, Matteo Destro, Francesca Di Lupo, Nadia Garino, Giuseppina Meligrana, Carlotta Francia and Claudio Gerbaldi
Affiliation: Department of Applied Science and Technology, Politecnico di Torino, and Center for Space Human Robotics @Polito, Istituto Italiano di Tecnologia, Torino, Italy
Abstract: Polymer electrolytes possess the best combination of desirable properties for Li-ion batteries. In fact they can offer all-solid-state construction, wide variety of shapes and sizes, light-weight, low-cost of fabrication, high safety and high energy density. In the present scenario, thermo-set membranes prepared by UV-curing method could be an interesting alternative to the existing products, as this versatile polymerization technique permits the formation of solid cross-linked film in a very short time with high efficiency and eco-friendliness as the use of solvent is avoided. In this work we describe the synthesis and the electrochemical characterization of polymer electrolyte membranes based on different methacrylic monomers and oligomers with several kinds of additives such as ionic liquids, organic plasticizers and natural fillers. We also demonstrate a huge improvement in mechanical properties by reinforcement with cellulose hand-sheets.
The ionic conductivity of the membranes at different temperatures was very high and displayed an average value of about 10-3 Scm-1 at ambient temperature. The anodic breakdown voltage was very high along with good cyclability in lithium cells at different temperatures. The galvanostatic cycling tests were conducted by constructing a laboratory scale lithium cell using LiFePO4 as cathode and a lithium disc or graphite as anode with the polymer electrolyte membrane as separator. The results obtained demonstrated that UV curing is a well suited method for an easy and rapid preparation of polymer electrolyte membranes for lithium based battery application.

Title: Review on Gel Polymer Electrolytes for Lithium/Sulfur Batteries
Author: Pu Chen
Affiliation: Canada Research Chair in Nano-Biomaterials, Department of Chemical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario, Canada; E-Mail: p4chen@uwaterloo.ca
Abstract: This paper reviews the advantages and characteristics of gel polymer electrolytes used in lithium/sulfur batteries. It encompasses five polymer hosts: poly (ethylene oxide) (PEO), poly (acrylonitrile) (PAN), poly (methyl methacrylate) (PMMA), poly (vinylidene fluoride) (PVdF) and poly (vinylidene fluoride-hexafluoro propylene) (PVdF-HFP), when preparing the electrolyte. The physical and electrochemical properties of the gel polymer electrolytes are covered. And the electrochemical characteristics of the Li/S batteries using such a gel polymer electrolyte are discussed in detail.

Type of Paper: Article
Title: Polymer Electrolyte Membranes for High-Temperature Proton Exchange Membrane Fuel Cells
Authors: Panagiotis Trogadas and Thomas F. Fuller
Affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract: The polymer electrolyte fuel cell (PEFC) is considered as a clean and highly efficient power generation technology for the 21st century. Present PEFC technology is based on perfluorinated ionomer membranes operating at 80 ^oC. The main characteristics (structure and properties) and problems of Nafion^®-based PEFC technology are discussed. Today, research is focused on developing PEFCs operating at high temperatures (above 100 ^oC). Elevated temperatures can enhance electrochemical reactions, improve water management and gas transport, and increase CO tolerance. However, Nafion^® is prone to rapid dehydration at high temperatures resulting in significant conductivity and performance losses, and thus alternative candidates are being investigated. The alternative polymer membranes can be classified into three categories: i) modified Nafion^® membranes with hygroscopic metal oxide particles, ii) sulfonated aromatic hydrocarbons, as well as iii) acid-base and blend polymers. These materials are reviewed in this article.

Type of Paper: Review
Title: Progresses in Membrane Systems
Author: Enrico Drioli
Affiliation: Institute for Membrane Technology ITM-CNR, c/o University of Calabria, Via Pietro Bucci CUBO 17/C, 87030 Rende (CS), Italy
Abstract: Nowadays supply of energy, environmental protection and fresh water are three keys elements for the sustainable development of every Society. The possible solutions for the mentioned challenges should follow process intensification (PI) strategy, a design approach offering concrete benefits in manufacturing and processing, substantially shrinking equipment size, boosting plant efficiency, saving energy, reducing capital costs, increasing safety, minimizing environmental impact and maximizing the raw materials exploitation. Membrane engineering can play important role for dealing with the mentioned challenges. On the one hand, membrane engineering has a much wider spectrum of potential applications as unit operations in process engineering than in other technological areas and the roles of membrane are not restricted to molecular separation any more. On the other hand, membrane processes can very well address the goals of PI because membrane processes have enough potential to substitute large, expensive, high energy consumption and high pollutant process with less cost, less pollutant, small foot print, more efficient and highly safe process. Membrane operations can be used to conduct molecular separations (microfiltration, ultra filtration, reverse osmosis, etc.), chemical transformations (membrane reactors, catalytic membranes, membrane bioreactors, etc.), and mass and energy transfer between different phases (membrane contactor, membrane distillation, membrane crystallizer, membrane emulsifiers, membrane strippers, membrane scrubbers, etc.) and as new field for energy production (Forward Osmosis, Reverse Electro dialysis) from salinity gradient and from converting chemical energy in electricity (Fuel cell, Lithium ion battery, etc.) At the moment membrane process is finding their position in separation process (which consume around 40–50% of energy used in industry) and in comparison with thermal driven separation an order of magnitude reduction in energy use can be obtained. For example the Chloro Soda process has been redesigned based on the membrane system or Reverse Osmosis desalination system (with an energy consumption of only 2.2 (kw hr)/m3) is over 10 fold more efficient than the thermal approach. In addition integrated systems of membrane operations provides unique opportunities for improving water quality and reducing cost, for increasing recovery factor and decreasing brine disposal problem, approaching the concept of “zero-liquid-discharge”, “total raw materials utilization” and “low energy consumption in seawater desalination. Producing crystal (Lithium, Magnesium, etc.) from seawater through membrane operations not only can overcome the brine disposal problem but also make sea as a new source of raw material production. In this area the products of membrane operations is competitive with traditional crystallization method.

Type of Paper: Article
Title: Anion- or Cation-Exchange Membranes for NaBH₄/H₂O₂ Fuel Cells?
Authors: Diogo Miguel Franco dos Santos *, A.L. Morais, B. Šljukić and C.A.C. Sequeira
Affiliation: ICEMS, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049–001 Lisboa, Portugal; E-Mail: diogosantos@ist.utl.pt
Abstract: Direct borohydride fuel cells (DBFCs), which operate on sodium borohydride (NaBH₄) as the fuel and hydrogen peroxide (H₂O₂) as the oxidant, are getting increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One of the key factors to improve the performance of DBFCs concerns the type of the used separator. Both anion- and cation-exchange membranes may be considered as separators for the DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH₄/H₂O₂ fuel cells using platinum electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001) and a cation-exchange membrane (CMI-7000), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC’s performance. Cell polarisation, power density, stability, and durability tests are used for the membranes’ evaluation. In the absence of an electric field, reasonable cell stabilities are attained; in the presence of high currents, cell voltages drop quickly, limiting the cell operation to shorter duration times. Energy densities and specific capacities are estimated for a 2 h-cell operation. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation these membranes seem to outperform the stability of the benchmark Nafion membranes but further optimisation is required to improve their instantaneous power load.

Type of Paper: Article
Title: Electrochemical Activities of MEA Followed by Function of Temperature and Humidity
Authors: Uma Thanganathan¹, Javier Parrondo ² and Bobba Rambabu ²
Affiliation: ¹ Research Core for Interdisciplinary Sciences (RCIS), Okayama University, Tsushima-Naka, Kita-Ku, Okayama, 700-8530, Japan; E-Mails: umthan09@cc.okayama-u.ac.jp
² Solid State Ionics Laboratory, Department of Physics, Southern University and A&M College, Baton Rouge, Louisiana, 70813, USA; E-Mails: javier_parrondo@hotmail.com (J.P.); rambabu@cox.net (B.R.)
Abstract: Performed a single cell performances using membrane-electrode-assemble (MEA) under various operating conditions such as the effect of temperatures and relative humidity and finally calculated the water weight percentage of the MEA. In this object, a high proton-conducting composite membrane electrolyte was introduced for MEA, and Pt/C catalyst displayed the cell performances at low temperatures. The performance of hybrid membrane electrolyte was evaluated by comparing with that of the standard Nafion^Ò membrane and similar research work under identical test conditions. This MEA was performed a high current density of 300 mA/cm² at 60 °C and 100% RH. In this paper, the membrane properties such as I–V profile and water weight percentage and related them to fuel cell performances of MEAs.