Abstract
Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce0.8Gd0.2O2−δ–CoFe2O4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopant and depletion of oxygen vacancies at the Ce0.8Gd0.2O2−δ–Ce0.8Gd0.2O2−δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. This work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution.
Highlights
Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage
We correlated the performance of CGO–CFO composite Mixed ionic–electronic conductors (MIECs) with the charge distribution near the CGO–CGO grain boundaries and the structure of the newly formed GFCCO phase using spatially resolved energy dispersive X-ray spectrometry (EDX)/energy loss spectroscopy (EELS), HADDF-scanning transmission electron microscopy (STEM) imaging and selected area electron diffraction (SAED)
The synergistic effect of fast oxygen transport in CGO–CGO, CGO– GFCCO grain boundaries, and the GFCCO6040 phase in CGO– CFO6040 results in the highest oxygen flux observed in the CGO–AFe2O4 materials system
Summary
Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. The formation of an emergent phase successfully avoids segregation of the Gd dopant and depletion of oxygen vacancies at the Ce0.8Gd0.2O2 À d–Ce0.8Gd0.2O2 À d grain boundary. Mixed ionic–electronic conductors (MIECs) are widely used in semiconductors, electrochemical energy storage materials, electrodes of fuel cells and batteries, separation membranes and catalysts with various requirements for chemical, electrical, thermal and mechanical properties[1,2,3,4,5,6,7,8,9,10,11]. Property tuning appears to be flexible and straightforward in dual-phase MIECs (DP-MIECs), as both the ionic conductors and the electronic conductors have been well developed for many decades[13,14,15,16]
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