High-Conductive Protonated Layered Oxides from H₂ O Vapor-Annealed Brownmillerites

Protonated 3d transition-metal oxides often display low electronic conduction, which hampers their application in electric, magnetic, thermoelectric, and catalytic fields. Electronic conduction can be enhanced by co-inserting oxygen acceptors simultaneously. However, the currently used redox approaches hinder protons and oxygen ions co-insertion due to the selective switching issues. Here, a thermal hydration strategy for systematically exploring the synthesis of conductive protonated oxides from 3d transition-metal oxides is introduced. This strategy is illustrated by synthesizing a novel layered-oxide SrCoO₃ H from the brownmillerite SrCoO_2.5 . Compared to the insulating SrCoO_2.5 , SrCoO₃ H exhibits an unprecedented high electronic conductivity above room temperature, water uptake at 250 °C, and a thermoelectric power factor of up to 1.2 mW K^-2 m^-1 at 300 K. These findings open up opportunities for creating high-conductive protonated layered oxides by protons and oxygen ions co-doping.