Measurement of overpotentials in solid oxide cells is typically done by placing a reference electrode on the surface of the cell or by extracting the information from electrochemical impedance spectroscopy (EIS). However, neither of these methods afford measurement of thermodynamic potentials inside the solid electrolyte. As a result, changes in thermodynamic potentials across electrode/electrolyte interfaces cannot be measured by either external reference electrodes or EIS. Embedded probes in principle can be used to estimate electric potential (inclusive of local electron chemical potential) and chemical potential of electrically neutral species corresponding to the mobile species. This has been done decades ago on cation conductors such as silver sulfide. We report on the measurement of electron electrochemical potential and oxygen chemical potential in solid electrolytes of thin, anode-supported solid oxide fuel cells, electrolyzers and oxygen separators. This is achieved by embedding platinum probes within the thin electrolyte membranes. Electric potentials are measured in SOFC and in driven fuel cell modes. It is shown that the measured potential depends upon the electronic conductivity of the solid electrolyte. Finite Element Method (FEM) analysis is conducted of embedded probes, taking into account both geometry and the nature of the probe. The analysis is based on numerically solving relevant differential equations that describe the variation of two thermodynamic potentials. Two types of probes are examined: (a) An inert metallic probe (e.g. Pt) coated by an electrically insulating coating but with the tip contacting the electrolyte measures the local electrochemical potential of electrons. (b) A hollow Pt probe coated by an electrically insulating coating but with a tip made of a purely oxygen ion conductor in contact with the electrolyte which measures the local oxygen chemical potential. Our long range objective is to fabricate cells with embedded probes using nan-fabrication methods.

Measurement of thermodynamic potentials in solid oxide electrolytes by embedded probes: Experimental measurements and finite element modeling

247th National Meeting (2014)

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