Materials for fuel-cell technologies
TL;DR: Recent progress in the search and development of innovative alternative materials in the development of fuel-cell stack is summarized.
Abstract: 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.
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TL;DR: It is reported that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.
Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.
6,370 citations
TL;DR: The notion of sustainability is introduced through discussion of the energy and environmental costs of state-of-the-art lithium-ion batteries, considering elemental abundance, toxicity, synthetic methods and scalability.
Abstract: Energy storage using batteries offers a solution to the intermittent nature of energy production from renewable sources; however, such technology must be sustainable. This Review discusses battery development from a sustainability perspective, considering the energy and environmental costs of state-of-the-art Li-ion batteries and the design of new systems beyond Li-ion. Images: batteries, car, globe: © iStock/Thinkstock.
5,271 citations
TL;DR: Fossil fuels currently supply most of the world's energy needs, and however unacceptable their long-term consequences, the supplies are likely to remain adequate for the next few generations.
Abstract: Fossil fuels currently supply most of the world's energy needs, and however unacceptable their long-term consequences, the supplies are likely to remain adequate for the next few generations. Scientists and policy makers must make use of this period of grace to assess alternative sources of energy and determine what is scientifically possible, environmentally acceptable and technologically promising.
4,005 citations
TL;DR: The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward a series of key clean energy conversion reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties.
Abstract: A fundamental change has been achieved in understanding surface electrochemistry due to the profound knowledge of the nature of electrocatalytic processes accumulated over the past several decades and to the recent technological advances in spectroscopy and high resolution imaging. Nowadays one can preferably design electrocatalysts based on the deep theoretical knowledge of electronic structures, via computer-guided engineering of the surface and (electro)chemical properties of materials, followed by the synthesis of practical materials with high performance for specific reactions. This review provides insights into both theoretical and experimental electrochemistry toward a better understanding of a series of key clean energy conversion reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward the aforementioned reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties. Also, a rational design of electrocatalysts is proposed starting from the most fundamental aspects of the electronic structure engineering to a more practical level of nanotechnological fabrication.
3,918 citations
TL;DR: The electrocatalytic trends established for extended surfaces are used to explain the activity pattern of Pt(3)M nanocatalysts as well as to provide a fundamental basis for the catalytic enhancement of cathode catalysts.
Abstract: One of the key objectives in fuel-cell technology is to improve and reduce Pt loading as the oxygen-reduction catalyst. Here, we show a fundamental relationship in electrocatalytic trends on Pt(3)M (M=Ni, Co, Fe, Ti, V) surfaces between the experimentally determined surface electronic structure (the d-band centre) and activity for the oxygen-reduction reaction. This relationship exhibits 'volcano-type' behaviour, where the maximum catalytic activity is governed by a balance between adsorption energies of reactive intermediates and surface coverage by spectator (blocking) species. The electrocatalytic trends established for extended surfaces are used to explain the activity pattern of Pt(3)M nanocatalysts as well as to provide a fundamental basis for the catalytic enhancement of cathode catalysts. By combining simulations with experiments in the quest for surfaces with desired activity, an advanced concept in nanoscale catalyst engineering has been developed.
2,774 citations
References
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01 Jan 2000
TL;DR: In this paper, the first edition of this paper, the authors presented an analysis of fuel cell systems and their performance in terms of Molar Gibbs Free Energy Calculations (GFE) and Open Circuit Voltage.
Abstract: Preface. Foreword to the first edition. Acknowledgements. Abbreviations. Symbols. Introduction. Efficiency and Open Circuit Voltage. Operational Fuel Cell Voltages. Proton Exchange Membrane Fuel Cells. Alkaline Electrolyte Fuel Cells. Direct Methanol Fuel Cells. Medium and High Temperature Fuel Cells. Fuelling Fuel Cells. Compressors, Turbines, Ejectors, Fans, Blowers, and Pumps. Delivering Fuel Cell Power. Fuel Cell Systems Analysed. Appendix 1: Change in Molar Gibbs Free Energy Calculations. Appendix 2: Useful Fuel Cell Equations. Index.
4,202 citations
"Materials for fuel-cell technologie..." refers methods in this paper
...It is important to note that the materials currently being used in PEMFC, MCFC and tubular SOFC prototype demonstration units essentially remain the same as those selected at least 25 years ag...
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TL;DR: In this paper, the authors explain the transport properties and the swelling behaviour of NAFION and different sulfonated polyetherketones in terms of distinct differences on the microstructures and in the p K a of the acidic functional groups.
2,755 citations
"Materials for fuel-cell technologie..." refers background in this paper
...Phosphoric acid and polymers with immobilized heterocycles exhibit a conduction mechanism relying on structure diffusio...
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TL;DR: In this article, the authors evaluated thermodynamic and electrical conductivity data to select the most appropriate electrolyte composition for IT-SOFC operation at 500°C and found that the Gd 3+ ion is the preferred dopant, compared to Sm 3+ and Y 3+, at this temperature.
1,888 citations
TL;DR: In this paper, the authors reported the direct electrochemical oxidation of methane in solid oxide fuel cells that generate power densities upto 0.37 W cm−2 at 650°C.
Abstract: Fuel cells constitute an attractive power-generation technology that converts chemical energy directly and with high efficiency into electricity while causing little pollution. Most fuel cells require hydrogen as the fuel, but viable near-term applications will need to use the more readily available hydrocarbons, such as methane. Present-day demonstration power plants and planned fuel-cell electric vehicles therefore include a reformer that converts hydrocarbon fuel into hydrogen. Operating fuel cells directly on hydrocarbons would obviously eliminate the need for such a reformer and improve efficiency. In the case of polymer-electrolyte fuel cells, which have been studied for vehicle applications, the direct use of methanol fuel has been reported, but resulted in fuel permeating the electrolyte1,2. Solid oxide fuel cells — promising candidates for stationary power generation — can also use hydrocarbon fuel directly to generate energy, but this mode of operation resulted in either carbon deposition at high temperatures or poor power output at low operating temperatures3,4,5. Here we report the direct electrochemical oxidation of methane in solid oxide fuel cells that generate power densities upto 0.37 W cm−2 at 650 °C. This performance is comparable to that of fuel cells using hydrogen6,7 and is achieved by using ceria-containing anodes and low operating temperatures to avoid carbon deposition. We expect that the incorporation of more advanced cathodes would further improve the performance of our cells, making this solid oxide fuel cell a promising candidate for practical and efficient fuel-cell applications.
1,194 citations