Reversible Electrochemical Cells for Fuel to and from Electricity

Over the past decade, the availability of electricity from sustainable energy sources has risen dramatically while the cost has fallen steeply. These factors have driven a surge in activity in the development of energy storage technologies. While much of this effort has been directed towards gridscale batteries, reversible hydrogen electrochemical cells offer untapped opportunities. In particular, electrochemical cells based on proton conducting ceramic oxides are attractive candidates for interconversion between hydrogen and electricity. When operated to produce electricity these function as fuel cells, and when operated to create hydrogen, they function as electrolysis cells. The proton conducting nature of the electrolyte provides inherent advantages in the gas flow configuration over traditional oxide cells in which the electrolyte is an oxygen ion conductor. However, despite high conductivity in protonic ceramic oxides, electrochemical performance as reported in the open literature has remained low. Moreove, the most commonly pursued electrolyte compositions suffer from poor chemical stability. We describe here recent progress achieved using a combination of three advances: a new electrolyte composition, a new air electrode, and processing methods to decrease the contact resistance between these two components. The resulting cells display exceptional power densities in fuel cell mode, and extremely high electricity-to-hydrogen conversion efficiency in electrolysis mode. In addition, the cells are extremely stable over hundreds of hours of operation. As such, protonic ceramic electrochemical cells are likely to play a major role in a sustainable energy future.