Protonic ceramic fuel cells: design analysis from cells to systems

Abstract

This thesis informs fundamental hypotheses about protonic ceramic cell failures and potential design solutions. A multi-physics, material mechanics model of protonic ceramic membrane structures is developed to predict chemo- and thermo-mechanical stresses arising from incorporation and transport of defects within button cell during both fabrication and operation. The model results and analysis provide valuable insight into cell design and fabrication steps which can help alleviate material stresses which lead to mechanical failure. While thermal expansion has a higher contribution to stress than chemical expansion, effects from chemical expansion cannot be neglected. In addition, previously developed cell and stack models are used to estimate performance prediction from button cell experimental data to full-scale cells and stacks. Electrochemical cell models are calibrated from button cells operating over a range of temperatures and on methane/steam gas mixtures. The cell-level electrochemical model is coupled to a one-dimensional, channel-level interface charge transfer model to enable prediction of streamwise distributions of gas composition, current density, temperature, pressure, and mass flow. The model is used to: (1) support manufacturing cost estimates of 5 kW PCFC stacks in mass production, (2) PCFC system design and performance estimation, and (3) techno-economic analysis of Nth generation, PCFC-based, stationary distributed power generation systems in 5-25 kW range. PCFC stack production cost estimates are found to be as much as 27-37\% lower at 550{\textdegree}C than SOFCs operating at 800{\textdegree}C. Results of system design and performance analysis illustrate the importance of fuel utilization and show that system electric efficiencies of greater than 70\% are possible without hybridization with other prime movers. Optimal cell voltage of 0.78V, a high cell temperature and lower excess air ratio promote lower CAPEX and LCOE. The PCFC lower operating temperature and potentially higher achievable fuel utilization could be a determinant factor for future commercialization.