An operando confocal micro-Raman spectroscopy cell for intermediate temperature MIEC membrane development
Abstract
This STIR proposal aims to advance ceramic membranes for air separation for intermediate temperature (500-650¡C) energy conversion devices requiring pure oxygen. The strategy is dual-phase mixed ionic electronic conducting (MIEC) membranes catalyzed on both sides for interfacial oxygen exchange. Dual-phase MIECs have advantages of thermomechanical stability, absolute oxygen selectivity and simplicity of use. There is no need for the external wiring required by electrochemical oxygen pumps (e.g., solid oxide fuel cells operated in reverse). Electronic and ionic conductivities are inherent to MIEC structures comprising both fluorite and perovskite phases. The obstacle to commercialization of intermediate temperature MIECs is degradation of transference-number-equivalence for ionic/electronic conductivity, thermal stability of catalytic surfaces required for oxygen exchange at the air-feed and oxygen-sweep stream sides respectively and finally overall performance. The STIR objective is design, assembly and demonstration of a high temperature cell with a (1) flexible feed stream manifold that enables use of a selected MIEC membrane side as either the air-feed side or the oxygen-permeate side and (2) a quartz window enabling operando Raman spectroscopy of the MIEC surfaces. Assembly and validation of the operando cell, using a well-documented dual-phase MIEC, will enable mechanistic studies of the oxygen exchange reactions and study of phase changes occurring in the interfacial region encompassing the MIEC/catalytic-layer. The project objectives are: 1:Assemble high temperature cell for oxygen flux measurements simultaneous with operando Raman spectroscopy of the air-feed or permeate side of the MIEC. 2:Validate the operando spectroscopy/flux measurement cell and MIEC disk preparative methods using a well characterized and documented dual phase MIEC. 3:Obtain preliminary spectroscopic data on reversible oxygen vacancy generation and degradation mechanisms. We will extend our operando spectroscopy expertise to the study of dual-phase MIECs used for air separation. The significance of this advancement follows: Our understanding of MIEC oxygen exchange reactions (i.e. ORR and OER) and phase equilibria at the feed and permeate sides of the membrane will be advanced. Raman spectroscopy is an excellent probe of oxygen vacancies and oxide crystallinity. We anticipate observation of a Raman band near 460 cm-1 attributed to the breathing mode of the 8 oxygen atoms around the fluorite structure CeIV atoms. We expect to elucidate factors that cause this peak to shift and broaden. The fluorite structure will be doped with trivalent lanthanides (e.g., Gd, Sm, Pr) to generate the oxygen vacancies required for oxide ion transport. The extent of this doping will shift the frequency of the breathing mode. At the permeate side, where the partial pressure of oxygen is lower, CeIV can be reduced to CeIII. This will generate additional oxygen vacancies. Additionally, the higher ionic radius of CeIII will result in lattice expansion. These structural alterations are known to impact the Raman profile. Thus the 460 cm-1 band shift may be a direct probe of oxygen vacancies, particle size and crystallinity. Operando spectroscopy at the feed and permeate side of the MIEC will elucidate bands due to the fluorite and perovskite structures of the dual-phase MEIC membranes. We expect to see degradation of the permeate rate with time. Correlation of flux degradation data with Raman spectroscopy is expected to provide information concerning the mechanism of flux degradation. This work contributes to the ArmyÕs fuel cell program, ...
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 11, 2018
- Source ID
- W911NF1710557
Entities
People
- Eugene S Smotkin
Organizations
- Army Contracting Command
- Northeastern University
- United States Army