ALD for clean energy conversion, utilization, and storage
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Introduction The enormous energy needs of modern society pose some of the most vexing problems facing mankind today. It is essential to the health of our economy and our climate that we develop alternatives to fossil fuels, as well as new means for storing and conserving energy in renewable and economically viable ways. It is not enough to simply engineer existing technologies to solve these difficult challenges. For instance, to manufacture enough crystalline silicon solar cells to supply the world’s energy would consume roughly the entire global GDP.1 Instead, revolutionary innovations in technology are required so that solar cells, fuel cells, and other energy devices can be manufactured cheaply and on a massive scale, while maintaining high performance. New materials will drive the revolution in energy technology. In particular, nanomaterials with tunable structure, porosity, and composition hold tremendous promise. Atomic layer deposition (ALD) provides the capability to synthesize nanomaterials literally at the atomic level. ALD utilizes self-limiting chemical reactions to achieve atomic-level control over film thickness and composition without the need for line-of-site access to the precursor source.2,3 As a result, ALD could play a key role in achieving the breakthroughs in materials synthesis necessary to solve our energy problems. This article will survey recent work in the field of ALD for clean energy, including research and development in fuel
cells, batteries, photovoltaics, and catalysts. This is not a comprehensive review,2–4 but rather a set of examples illustrating the advantages afforded by ALD in nanomaterials for energy, intended to encourage the reader to pursue these topics more deeply. In the following sections, we will emphasize the particular attributes of ALD (e.g., conformality and thickness control) that make this technology attractive for particular applications.
ALD for solid oxide fuel cells A fuel cell is an electrochemical device that directly converts chemical energy into electrical energy, which can be used to perform work on an external load. Fuel cells have the potential to achieve high efficiencies to provide a scalable, clean power supply. A basic fuel cell consists of an ion-conducting electrolyte, which separates the anode (fuel side) and cathode (oxidant side) of the cell. In addition, catalysts are often incorporated into the electrode structures to facilitate charge transfer reactions during operation. Among fuel cell types, solid oxide fuel cells (SOFCs) are attractive due to fuel flexibility, nonprecious metal catalysts, minimal fuel crossover, and high efficiencies. SOFCs incorporate a ceramic electrolyte, and therefore typically operate at elevated temperatures (>700°C) to achieve sufficient ionic conductivities. However, the high temperature requirements limit their application to large, stationary sources. Therefore, many research efforts are focused on intermediate-temperature
Jeffrey W. Elam, Argonne National Laboratory, Argonne, IL 60439, USA; [email protected] Neil P.
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