Metal Hydride Reclamation from Ni-MH batteries for Small-Scale Power Generation

Electrification of rural communities and technologically- or economically-developing countries can be limited by the pace of infrastructure installation. Point-of-use power generation from hydrogen fuel cells offers a scalable solution provided the design is low-cost, safe, and robust. A major source of cost and reliability issues is the hydrogen storage technology itself, with the current state-of-the-art being high-pressure gas storage in composite tanks [1,2]. The balance-of-plant components for compression, filling, temperature and pressure regulation, and safety only add to the cost and complexity. Hydrogen storage in intermetallic metal hydrides (MH), a class of materials which store hydrogen interstitially in a metal alloy, circumvents the issues related to high pressures by targeting a hydrogen release pressure equivalent to fuel-cell operational requirements. MH storage for fuel cell generation has been explored and initial reports suggest a reduction in cost and safety is possible with the correct selection of the MH alloy [1–3]. Leading candidates for MH storage are LaNi₅-based AB₅ alloys which have favorable kinetics, cycle life, and hydrogen release pressures [4,5]. However, the monetary and environmental costs of rare-earth mining, and competition for other applications of rare-earth metals were not considered in previous analyses.<br/>Here, I present an alternative source for AB₅ MH alloys – discarded hybrid electric vehicle (HEV) batteries. HEV like the Toyota Prius utilize the Ni-MH battery chemistry with AB₅ alloys in a cathode-limited design. Prius batteries alone contain up to 8 million kg of AB₅ MH, representing 3850 MWh of power generation from fuel cells [6]. I will demonstrated that AB₅ MH recovered from end-of-life Toyota Prius battery modules readily absorb and desorb hydrogen and retain the AB₅ crystal structure with limited La(OH)₃ corrosion product. Furthermore, I will present structural, spectroscopic, and hydrogen capacity and release characterization of these AB₅MHs and assess the feasibility for re-use as gas-phase hydrogen storage materials. Finally, I will contextualize the approach proposed here within the established field of rare-earth recovery from e-waste.<br/><br/>[1] K. Kubo, Y. Kawaharazaki, and H. Itoh, International Journal of Hydrogen Energy <b>42</b>, 22475 (2017).<br/>[2] G. Han, Y. Kwon, J. B. Kim, S. Lee, J. Bae, E. Cho, B. J. Lee, S. Cho, and J. Park, Applied Energy <b>259</b>, 114175 (2020).<br/>[3] E. MacA. Gray, C. J. Webb, J. Andrews, B. Shabani, P. J. Tsai, and S. L. I. Chan, International Journal of Hydrogen Energy <b>36</b>, 654 (2011).<br/>[4] K. Beard, <i>Linden’s Handbook of Batteries</i>, 5th ed., Vol. Section D: Nickel-Metal Hydride (McGraw-Hill Education, 2019).<br/>[5] K. Young and J. Nei, Materials <b>6</b>, 4574 (2013).<br/>[6] E. L. Schneider, W. Kindlein, S. Souza, and C. F. Malfatti, Journal of Power Sources <b>189</b>, 1264 (2009).