RETRACTED: Proton transport enabled by a field-induced metallic state in a semiconductor heterostructure

A metallic route for protons The operating temperatures of solid oxide fuel cells are usually much higher than needed to drive the uncatalyzed electrochemical reaction to transport oxygen anions or protons through ceramic electrolytes. Wu et al. report that the interface between two semiconductors, Na x CoO 2 and CeO 2 , forms a metallic state that enables proton transport at temperatures below 600°C (see the Perspective by Ni and Shao). The authors constructed a hydrogen fuel cell with this material that delivered 1 watt per centimeter. Science , this issue p. 184 ; see also p. 138