How does small-polaron conduction help solid oxide fuel cell anodes conduct electricity?

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conductive ceramics Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.

In solid oxide fuel cells (SOFCs), anode materials must function as excellent electronic conductors to facilitate the electrochemical process. Small-polaron conduction enables this by allowing electrons to move between two different valence states of the transition metal constituents within the ceramic material.1

This mechanism involves the "hopping" of electrons or electron holes between these valence states. As these charge carriers move through the crystal lattice, they create small regions of local polarization, which are referred to as polarons. By facilitating this electron transfer, small-polaron conduction provides the necessary electronic conductivity for the ceramic anodes to effectively transport current within the fuel cell structure.231