Professor Sossina M. Haile

Professor Sossina M. Haile
Department of Materials Science & Engineering
Northwestern University
Abstract

Superprotonic Solid Acid Compounds for Sustainable Energy Technologies 

Superprotonic solid acid electrolytes, materials with chemical and physical properties intermediate between conventional acids (e.g., H3PO4) and conventional salts (e.g., Cs3PO4), have emerged as attractive candidates for fuel cell and other electrochemical applications. Key characteristics of these materials, which include CsHSO4, Cs3H(SeO4)2, CsH2PO4, and Cs2(HSO4)(H2PO4), are tetrahedral oxyanion groups linked by hydrogen bonds and a polymorphic structural transition to a disordered state at moderate temperatures. In the high temperature state, rapid oxyanion reorientation and dynamic disorder of the hydrogen bond network facilitate high proton conductivity. The transition to the structurally disordered phase is accompanied by a jump in conductivity by 3-5 orders of magnitude, and the activation energy for proton transport drops to a value of ~ 0.35 eV. Of materials displaying such behavior, CsH2PO4 is of particular technological significance is due to its chemical stability against both oxidation and reduction in device- relevant environments. We present here an overview of the proton transport characteristics of CsH2PO4 and the current status of electrochemical technologies in which it has been deployed. Material limitations translate into device limitations, motivating our efforts to develop and discover new superprotonic conductors. We show that dramatic changes in phase behavior and proton conductivity of the base phosphate can be induced by only minor changes in chemistry, suggesting routes for tuning behavior to achieve desired outcomes.

Sossina M. Haile

Sossina M. Haile is the Walter P. Murphy Professor of Materials Science and Engineering at Northwestern University, a position she assumed in 2015 after serving 18 years on the faculty at the California Institute of Technology. She earned her Ph.D. in Materials Science and Engineering from the Massachusetts Institute of Technology and as part of her training spent two years at the Max Planck Institute for Solid State Research in Stuttgart, Germany. Haile’s research broadly encompasses materials, especially oxides, for sustainable electrochemical energy technologies. Amongst her many awards, in 2008 Haile received an American Competitiveness and Innovation Fellowship from the U.S. National Science Foundation in recognition of “her timely and transformative research in the energy field and her dedication to inclusive mentoring, education and outreach across many levels.” In 2010 she was the recipient of the Chemical Pioneer Award (American Institute of Chemists), in 2012 the International Ceramics Prize (World Academy of Ceramics), and in 2020 the Turnbull Lectureship (Materials Research Society). She is a fellow of the Royal Society of Chemistry, the Materials Research Society, the American Ceramics Society, the African Academy of Sciences, and the Ethiopian Academy of Sciences, and serves on the editorial boards of MRS Energy and Sustainability and Joule. 

Hosted by Professor Andreas Stein 

Learn more about the Margaret C. Etter Memorial Lecture in Materials Chemistry