Voltammetric Studies of Porous Molybdenum Electrodes for the Alkali Metal Thermoelectric Converter

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Abstract
Voltammetry of partially oxidized porous molybdenum alkali metal thermoelectric converter (AMTEC) electrodes from ∼600 to ∼1000 K revealed a series of redox processes within the operational voltage range of the AMTEC device. The most important of these processes involve reactions that add sodium to , , and . The redox processes can be used as an in situ analytical probe of oxide species in porous molybdenum electrodes. These constituents are important in establishing the electronic and ionic conductivities of AMTEC electrodes. The estimated equilibrium potentials of these reactions provide improved estimates of the free energies of formation of , , and . In the AMTEC operating regime, there is evidence for the comparatively slow corrosive attack by on molybdenum. The ionic conductivity of measured from 600 to over 1000 K shows sharp increases in conductivity at ∼750, 865, and 960 K. The conductivity is sufficiently large at to explain the observed electrochemical phenomena, as well as enhanced sodium transport in AMTEC electrodes below the freezing point (960 K) of . The results of this study are relevant to AMTEC device performance and also provide more detailed information about the ternary Na‐Mo‐O phase diagram in the range of conditions relevant to the AMTEC device.

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