Truly proton-conducting materials would have an immense impact on sustainable energy technologies for the 21st century, through efficient fuel cells, electrolyzers, and gas-separation membranes. However, proton conduction combined with materials stability seems difficult to achieve, and some hurdles and pathways are outlined in this article. Problems, possibilities, and artifacts of transport across and along interfaces are discussed, linked mainly to space-charge layer properties and engineering of the grain-boundary core and to water in nanovoids. The importance of protons in many semiconducting functional oxides is also explained. At lower temperatures and in humid environments, the presence of protonated cation vacancies (Ruetschi defects) is predicted and is expected to play an important role in photoelectrochemistry, catalysis, and surface transport.
Truls Norby can be reached at the Department of Chemistry, University of Oslo, FERMiO, Gaustadalleen 21, NO-0349 Oslo, Norway; tel. 47–22840654; fax 47–22840651; and e-mail [email protected]
Norby has been a professor in the Department of Chemistry at the University of Oslo since 1994 and head of the group for Solid-State Electrochemistry since 1997. He earned his PhD degree from the University of Oslo in 1986, where he studied and worked with the late Professor Per Kofstad. Norby works with thermodynamics and the transport of defects in oxides for fuel cells, electrolyzers, gas separation membranes, sensors, and protection layers. He specializes in protons in oxides and high-temperature proton conductors. Norby also has published approximately 130 journal papers, supervises roughly 15 master's and PhD degree students, and has founded the companies Protia AS and NorECs AS, which develop fuel cells and test equipment, respectively.