Materials challenges in the hydrogen cycle
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Energy Sector Analysis
Many technological and materials challenges remain to improve the generation, distribution, and storage of hydrogen and the manufacturability, durability, efficiency, and lifetime of fuel cells—all while reducing the cost.
Materials challenges in the hydrogen cycle By Tim Palucka Feature Editor: Brian J. Ingram
T
he term “hydrogen economy” was coined in 1970 by the University of Pennsylvania electrochemist Bernhardt Patrick John O’Mara Bockris. His vision was to provide clean power without the pollution generated by fossil fuel sources. Researchers have been exploring the hydrogen cycle since then, focusing on the need to efficiently generate, store, and distribute hydrogen for power generation, ammonia production, reduction of metals, and other applications. Materials development and discovery have been at the heart of these efforts. Perhaps the most successful technology has been the development and commercialization of fuel cells. At a fundamental level, fuel cells react with hydrogen and oxygen to generate electricity while producing water. They are being deployed more widely in transportation, industry, and home use than you might realize. The reduction of fossil fuels and their resulting pollutants is driving clean transportation initiatives worldwide and playing a big role in ushering in the long-awaited hydrogen economy. But there are many challenges to be met to make fuel cells energy- and cost-efficient: reducing the amount of expensive platinum catalyst, finding suitable nanoporous solid adsorbents or metal hydrides to make hydrogen storage practical, and discovering the best way to assemble the five-layer fuel-cell sandwich (membrane in the middle, electrodes on either side of the membrane, and gas diffusion media outside the electrodes) at large scale. Fuel cells are categorized by the membrane type and range from aqueous alkaline solutions, molten salts, polymers, to even solid crystalline materials. Two types of fuels cells—proton-exchange membrane (PEM) and solid-oxide fuel cells (SOFCs)—are widely used today and garner a lot of research investment. PEMs operate at a relatively low temperature (80°C) and use a polymer membrane; SOFCs have a ceramic membrane and operate at a higher temperature (800°C). Both have catalysts to accelerate hydrogen/ oxygen reaction. PEMs are used in transportation applications because the lower temperature makes startup instantaneous. With their higher temperature and longer startup time to reach it, SOFCs are more suitable for stationary, industrial applications. This article focuses on PEM fuel cells. According to E4Tech’s Fuel Cell Industry Review 2017, 72,600 fuel-cell units were shipped in 2017, broken down geographically by 56,800 units in Asia, 9900 in North America, 5100 in Europe, and 800 in the rest of the world. By application, 55,700 units were stationary, 12,000 were for transportation, and 4900 were portable units. The most common fuel cell shipped was the PEM variety
at 45,500 units, followed by 24,000 SOFCs, with the remaind
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