Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials.

Materials for fuel-cell technologies

A comprehensive review on PEM water electrolysis

Rod Borup is a Team Leader in the fuel cell program at Los Alamos National Lab in Los Alamos, New Mexico. He received his B.S.E. in Chemical Engineering from the University of Iowa in 1988 and his Ph.D. from the University of Washington in 1993. He has worked on fuel cell technology since 1994, working in the areas of hydrogen production and PEM fuel cell stack components. He has been awarded 12 U.S. patents, authored over 40 papers related to fuel cell technology, and presented over 50 oral papers at national meetings. His current main research area is related to water transport in PEM fuel cells and PEM fuel cell durability. Recently, he was awarded the 2005 DOE Hydrogen Program R&D Award for the most significant R&D contribution of the year for his team's work in fuel cell durability and was the Principal Investigator for the 2004 Fuel Cell Seminar (San Antonio, TX, USA) Best Poster Award. Jeremy Meyers is an Assistant Professor of materials science and engineering and mechanical engineering at the University of Texas at Austin, where his research focuses on the development of electrochemical energy systems and materials. Prior to joining the faculty at Texas, Jeremy workedmore » as manager of the advanced transportation technology group at UTC Power, where he was responsible for developing new system designs and components for automotive PEM fuel cell power plants. While at UTC Power, Jeremy led several customer development projects and a DOE-sponsored investigation into novel catalysts and membranes for PEM fuel cells. Jeremy has coauthored several papers on key mechanisms of fuel cell degradation and is a co-inventor of several patents. In 2006, Jeremy and several colleagues received the George Mead Medal, UTC's highest award for engineering achievement, and he served as the co-chair of the Gordon Research Conference on fuel cells. Jeremy received his Ph.D. in Chemical Engineering from the University of California at Berkeley and holds a Bachelor's Degree in Chemical Engineering from Stanford University. Bryan Pivovar received his B.S. in Chemical Engineering from the University of Wisconsin in 1994. He completed his Ph.D. in Chemical Engineering at the University of Minnesota in 2000 under the direction of Profs. Ed Cussler and Bill Smyrl, studying transport properties in fuel cell electrolytes. He continued working in the area of polymer electrolyte fuel cells at Los Alamos National Laboratory as a post-doc (2000-2001), as a technical staff member (2001-2005), and in his current position as a team leader (2005-present). In this time, Bryan's research has expanded to include further aspects of fuel cell operation, including electrodes, subfreezing effects, alternative polymers, hydroxide conductors, fuel cell interfaces, impurities, water transport, and high-temperature membranes. Bryan has served at various levels in national and international conferences and workshops, including organizing a DOE sponsored workshop on freezing effects in fuel cells and an ARO sponsored workshop on alkaline membrane fuel cells, and he was co-chair of the 2007 Gordon Research Conference on Fuel Cells. Minoru Inaba is a Professor at the Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Japan. He received his B.Sc. from the Faculty of Engineering, Kyoto University, in 1984 and his M.Sc. in 1986 and his Dr. Eng. in 1995 from the Graduate School of Engineering, Kyoto University. He has worked on electrochemical energy conversion systems including fuel cells and lithium-ion batteries at Kyoto University (1992-2002) and at Doshisha University (2002-present). His primary research interest is the durability of polymer electrolyte fuel cells (PEFCs), in particular, membrane degradation, and he has been involved in NEDO R&D research projects on PEFC durability since 2001. He has authored over 140 technical papers and 30 review articles. Kenichiro Ota is a Professor of the Chemical Energy Laboratory at the Graduate School of Engineering, Yokohama National University, Japan. He received his B.S.E. in Applied Chemistry from the University of Tokyo in 1968 and his Ph.D. from the University of Tokyo in 1973. He has worked on hydrogen energy and fuel cells since 1974, working on materials science for fuel cells and water electrolysis. He has published more than 150 original papers, 70 review papers, and 50 scientific books. He is now the president of the Hydrogen Energy Systems Society of Japan, the chairman of the Fuel Cell Research Group of the Electrochemical Society of Japan, and the chairman of the National Committee for the Standardization of the Stationary Fuel Cells. ABSTRACT TRUNCATED« less

Scientific aspects of polymer electrolyte fuel cell durability and degradation.

On the development of proton conducting polymer membranes for hydrogen and methanol fuel cells

Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

Polybenzimidazole films doped with phosphoric acid are being investigated as potential polymer electrolytes for use in hydrogen/air and direct methanol fuel cells. In this paper, we present experimental findings on the proton conductivity, water content, and methanol vapor permeability of this material, as well as preliminary fuel cell results. The low methanol vapor permeability of these electrolytes significantly reduces the adverse effects of methanol crossover typically observed in direct methanol polymer electrolyte membrane fuel cells.

https://iopscience.iop.org/article/10.1149/1.2044337/pdf

Acid-doped polybenzimidazoles : a new polymer electrolyte

Polybenzimidazole (PB1) film, a candidate polymer electrolyte membrane (PEM) for high-temperature (120-200°C) fuel cells, was cast from PBI/trifluoacetyl/H 3 PO 4 solution with constant molecular weight PBI powder and various acid doping levels. Conductivity measurements on these membranes were performed using an ac method under controlled temperature and relative humidity (RH). A complete set of conductivity data for H 3 PO 4 acid-doped PBI is presented as a function of temperature (60-200°C), RH (5-30%), and acid doping level (300-600 mol %). A mechanism of conductivity is proposed for the proton migration in this PBI/acid system based on this and previous work. Proton transfer in this system appears to occur along different paths for different doping levels, RHs, and temperatures. Hydrogen bonds immobilize the anions and form a network for proton transfer by a Grotthuss mechanism. The rate of proton transfer involving H 2 O is faster, leading to higher conductivity at higher RH. The order of the rate of proton transfer between various species is H 3 PO 4 (H 2 PO 4 -)...H-O-H> H 3 PO 4 ...H 2 PO - 4 > N-H + ...H 2 PO 4 - + N-H + ...H-O-H > N-H + ...N-H. The upper limit of proton conductivity is given by the conductivity of the liquid state H 3 PO 4 .

https://iopscience.iop.org/article/10.1149/1.1630037/pdf

Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells

A H2O2 fuel cell using acid doped polybenzimidazole as polymer electrolyte

In developing advanced fuel cells and other electrochemical reactors, it is desirable to combine the advantages of solid polymer electrolytes with the enhanced catalytic activity associated with temperatures above 100 C. This will require polymer electrolytes which retain high ionic conductivity at temperatures above the boiling point of water. One possibility is to equilibrate standard perfluorosulfonic acid polymer electrolytes such as Nafion, with a high boiling point Bronsted base such as phosphoric acid. The Nafion/H[sub 3]PO[sub 4] electrolyte has been evaluated with respect to water content, ionic conductivity and transport of oxygen, and methanol vapor. The results show that at elevated temperatures reasonably high conductivity (>0.05 [Omega][sup [minus]1] cm[sup [minus]1]) can be obtained. Methanol permeability is shown to be proportional to the methanol vapor activity and thus decreases with increasing temperature for a given partial pressure. Comparisons and distinctions between this electrolyte and pure phosphoric acid are also considered.

https://iopscience.iop.org/article/10.1149/1.2054875/pdf

A Polymer Electrolyte for Operation at Temperatures up to 200°C

Sol-gel derived Nafion/silica hybrid membranes were investigated as a potential polymer electrolyte for direct methanol fuel cell applications. Methanol uptake and methanol permeability were measured in liquid and vapor phase as a function of temperature, methanol vapor activity, and silica content. Decreased methanol uptake from liquid methanol was observed in the hybrid membranes with silica contents of 10 and 21 wt %. The hybrid membrane with silica content of ≈20 wt % showed a significant lower methanol permeation rate when immersed in a liquid methanol-water mixture at 25 and 80°C. Methanol uptake from the vapor phase by the hybrid membranes appears similar to that of unmodified Nafion. Methanol diffusion coefficients, as determined from sorption experiments, were slightly lower in the hybrid membranes than in unmodified Nafion. However, in direct permeation experiments, significantly lower methanol vapor permeability was seen only in the hybrid membrane with silica content of ≈20 wt %. Based on these results, Nafion/silica hybrid membranes with high silica content have potential as electrolytes for direct methanol fuel cells operating either on liquid or vapor-feed fuels. © 2001 The Electrochemical Society. All rights reserved.

Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Polymer Electrolyte Membrane Fuel Cell Applications: II. Methanol Uptake and Methanol Permeability

Jesse S. Wainright

Papers

Acid-doped polybenzimidazoles : a new polymer electrolyte

Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells

A H2O2 fuel cell using acid doped polybenzimidazole as polymer electrolyte

A Polymer Electrolyte for Operation at Temperatures up to 200°C

Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Polymer Electrolyte Membrane Fuel Cell Applications: II. Methanol Uptake and Methanol Permeability