Philosophical Magazine, Vol. 86, Nos. 6–8, 21 February–11 March 2006, 957–964 Hydrogen storage in Ti–Zr and Ti–Hf-based quasicrystals K. F. KELTON*y, J. J. HARTZELLy, R. G. HENNIGz, V. T. HUETTy and AKITO TAKASAKI} yDepartment of Physics, Washington University, St. Louis, MO 63130 zDepartment of Physics, Ohio State University, Columbus, Ohio 43210 }Department of Mechanical Engineering, Center for Energy Flow Research, Shibaura Institute of Technology, Fukasaku, Omiya, Saitama 337-8570, Japan (Received 15 May 2005; in final form 8 August 2005) The depletion of the world’s petroleum reserves and the increased environmental impact of conventional combustion-engine-powered automobiles are leading to renewed interest in hydrogen storage materials. In the mid 1990s, Ti/Zr/Hf-based quasicrystals were demonstrated to store more hydrogen than competing crystal intermetallic phases. Unfortunately, recovery of the hydrogen required temperatures in excess of 400  C, severely limiting the technological application of these materials. Here, the Ti/Zr-Hf-based quasicrystals and crystal approximants are reviewed and their hydrogenation properties are discussed. We also report the discovery of a relatively flat pressure plateau for hydrogenated TiZrNi quasicrystals at modest pressures (100–200 psi) that extends to hydrogen concentrations in excess of 4 wt.%. Approximately 2 wt.% of the hydrogen is easily recovered by heating at temperatures as low as 200  C. 1. Introduction Estimates vary on the timing, but all agree that the world’s petroleum reserves are within a few decades of severe depletion. This, the remarkably increasing demand from regions of the world outside the United States, particularly China, and the negative environmental impact of oil-based combustion engines, are forcing atten- tion toward the use of hydrogen as an alternate transportation fuel. Hydrogen contains three times the energy of conventional hydrocarbon fuels, and since the byproduct of hydrogen combustion with oxygen is water, the environmental impact is greatly reduced. Hydrogen storage is a key issue preventing the development of hydrogen- powered automobiles. The figure of merit for hydrogen-storage materials is the weight of the materials needed to store the hydrogen; recently, the US Department of Energy set a goal of 6.5 wt.% for transportation needs. Hydrogen atoms can be absorbed into either interstitial sites or on surfaces of materials. *Corresponding author. Email: kfk@wuphys.wustl.edu Philosophical Magazine ISSN 1478–6435 print/ISSN 1478–6443 online # 2006 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/14786430500300173