Wulff Lecture: Materials Innovations to the Rescue: Delivering ‘Green’ Hydrogen using Electrochemical Cells Built on Superprotonic Conductors
Sossina M. Haile, Walter P. Murphy Professor of Materials Science and Engineering, Northwestern University
Over the past decade, global CO2 emissions have continued to rise, while the costs of solar and wind electricity have fallen by about 90%. The challenge society thus faces is not in generating carbon-free electricity but in storing the electricity for use on demand. Electrolysis of water, or using electricity to split the H2O molecule into hydrogen and oxygen, has garnered renewed interest due to the suitability of hydrogen for long-term energy storage. Subsequent use of the hydrogen in fuel cells produces electricity at high efficiency without carbon emissions or the generation of other pollutants. Hydrogen, however, is difficult to transport, and its use in energy and related applications has been hindered by the lack of an appropriate delivery infrastructure. One solution that is gaining momentum is to use ammonia (NH3) as a carbon-free, easily liquified carrier of hydrogen. Success in this approach relies on the local conversion of the ammonia into nitrogen and ultra-high purity hydrogen. We describe here recent progress in the development of ammonia electrochemical conversion devices based on a solid-state proton-conducting electrolyte. The electrolyte material, cesium dihydrogen phosphate or CsH2PO4, displays unusually high proton conductivity as a result of rotational disorder of the (H2PO4)– groups, earning it the title ‘superprotonic.’ The devices are constructed similarly to batteries, with one electrode responsible for NH3 decomposition, the electrolyte responsible for delivering protons across the cell, and the other electrode responsible for H2 evolution. The hydrogen purity meets the high demands of fuel cell applications.
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 in 1992. Haile’s research broadly encompasses materials, especially oxides, for sustainable electrochemical energy technologies. Among her many awards, in 2008 Haile received an American Competitiveness and Innovation Fellowship from the U.S. National Science Foundation. In 2010, she received the Chemical Pioneer Award from the American Institute of Chemists. In 2012, she was awarded the International Ceramics Prize by the World Academy of Ceramics. In 2020, she received the Turnbull Award from the Materials Research Society. She is a fellow of the Materials Research Society, the American Ceramics Society, the Royal Society of Chemistry, the African Academy of Sciences, and the Ethiopian Academy of Sciences. She also serves on the editorial boards of Joule and MRS Energy and Sustainability.