Interstitial hydrides of high entropy alloys Aaron Keith 1,2 , M. Reece 1 , P. Á. Szilágyi 1,3 and C. Zlotea 2 1 Queen Mary University of London, UK, 2 Université Paris Est Créteil, CNRS, ICMPE, UMR 7182 France, 3 Department of Chemistry, University of Oslo, Norway Hydrogen is a desirable, versatile, and sustainable energy carrier, thanks to a variety of its properties. The wide- scale introduction of it as an energy vector, however, has been hindered as the cost-effective production and high- capacity storage is not yet commonplace. For vehicles, current storage methods use high pressures (700bar) 1 , cryogenic temperatures (20.28K) 1 , or both simultaneously. 1 As a result, improving the storage materials is vital. To that end, alternative techniques are due consideration, not least of which is solid-state storage within interstitial hydrides. Occupation of interstitial sites by hydrogen in binary metal alloys, e.g. LaNi 5 , 2 has shown a reasonable volumetric uptake of hydrogen. However, they utilise expensive, heavy, and scarce elements – rendering these compounds unsuitable for ubiquitous deployment. A solution addressing the three concerns of cost, mass, and scarcity of the elements used may come from High-Entropy Alloys (HEAs). 3 These multicomponent, solid solutions make use of elements with a high hydrogen affinity, e.g. Ti, Zr, Nb, 4 to achieve increased hydrogen uptakes relative to conventional alloys. 5 With recent examples highlighting the efficacy of HEAs to address the above concerns, the question remains; how can these alloys be engineered to achieve a higher hydrogen uptake? The presentation will discuss the efficacy of HEAs as hydrogen carriers and, by taking into consideration a priori design parameters (e.g. lattice structure, 6 randomness of elemental distribution, 7 stoichiometric variation 8 ) to discuss how they can be tailored to improve capacity and thermodynamic propertiess. References 1. K. Mazloomi and C. Gomes, Renewable and Sustainable Energy Reviews, 2012, 16, 3024-3033. 2. M. Tousignant and J. Huot, Journal of Alloys and Compounds, 2014, 595, 22-27. 3. F. Marques, M. Balcerzak, F. Winkelmann, G. Zepon and M. Felderhoff, Energy & Environmental Science, 2021, 14, 5191- 5227. 4. G. Driessen, Heat of Formation Models, Springer, Berlin, Heidelberg, 1988. 5. M. Sahlberg, D. Karlsson, C. Zlotea and U. Jansson, Scientific Reports, 2016, 6, 36770. 6. Y. F. Ye, Q. Wang, J. Lu, C. T. Liu and Y. Yang, Intermetallics, 2015, 59, 75-80. 7. Y. M. Zhang, Evans, J. R. G., Yang, S., The Journal of Crystallization Physics and Chemistry, 2010, 2, 103-119. 8. R. B. Strozi, D. R. Leiva, J. Huot, W. J. Botta and G. Zepon, International Journal of Hydrogen Energy, 2021, 46, 25555- 25561.
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