Giant conductivity enhancement of ferrite insulators induced by atomic hydrogen

Abstract

Hydrogen behavior in oxides has triggered much interest for its scientific and technological importance in a wide range of research fields from novel ion conductors to astrochemistry. Here, we report a giant conductivity enhancement in ZnFe₂O₄ ferrite insulators to the metallic state by over eleven orders of magnitude induced by electrochemically generated atomic hydrogen at room temperature. The conductivity and the amount of incorporated hydrogen increased in an exponential function with time. An activation energy for the atomic hydrogen chemisorption was measured to be 8.23 kJ mol⁻¹. Quantitative kinetics correlations among the adsorption of atomic hydrogen, hydrogen incorporation and conductivity enhancement are established, based on which hydrogen incorporation process is clarified herein. We demonstrate that the hydrogen incorporation in oxides can be adjusted by manipulating the kinetic factors. These findings have implications for research into hydrogen behavior in oxides in environments containing hydrogen atoms and offer possibilities for utilizing and controlling the modifications of oxide materials induced by atomic hydrogen.