Date of Award

Summer 2023

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Andreas Heyden

Abstract

Solid oxide fuel cells (SOFCs) have shown significant promise as a high efficiency energy conversion technology. SOFCs are solid-state, high temperature (600 – 1000 °C), and electrochemical conversion devices that can operate with a wide variety of fuels such as hydrogen, syngas, and hydrocarbon feedstocks. The state-of-the-art SOFC is manufactured with a lanthanum strontium manganite (LSM) cathode, an yttria-stabilizedzirconia electrolyte (YSZ), and a nickel on yttria-stabilized-zirconia (Ni/YSZ) cermet anode. LSM || YSZ || Ni/YSZ SOFCs operate at or above 800 °C to achieve sufficient oxide mobility. The high temperatures introduce problems such as long device start-up, particle sintering, and material degradation due to thermal stresses. To remedy these problems, ongoing SOFC research focuses on the intermediate temperature (IT) range between 600 and 800 °C. Intermediate range research primarily focuses on the discovery and design of novel materials for the anode, cathode, and electrolyte layers of the SOFC. This dissertation focuses on the material design of two promising classes of IT materials: the Ruddlesden-Popper (RP) phase and the cubic perovskite.

For the first aim, the bulk structural, electronic, and ionic conduction properties for the RP perovskite (Sr,Pr)2FeO4 (SPF) family are investigated as a function of Pr3+ concentration. For a given dopant-configuration, generalized gradient approximation-based density functional theory is used to model the relationship between Pr3+ concentration, iron oxidation state, and charge compensation with defect formation to explain doping trends for electronic and ionic conduction. For the second aim and to vi better understand how A-site doped RP materials behave as oxidation catalysts, SrLaFeO4is modeled to elaborate the oxidation mechanisms of hydrogen and syngas fuels. Two (001) Fe-terminated surface models are proposed that differ by the elemental identity of the underlying rocksalt layer. The FeO2-SrO (001) surface displays higher activity for both hydrogen and syngas oxidation relative to the FeO2-LaO (001) for all cell voltages including short circuit conditions. Lastly, for the third aim, a highthroughput approach is utilized to model 4793 unique perovskites elemental configurations in order to discover novel proton-conducting electrolyte materials. A filtering scheme based on electrical conductivity and thermodynamic stability under water-containing conditions yields 116 suitable configurations. For all passing configurations, oxygen vacancy defect and hydration formation are modeled to elaborate on trends related to proton conductivity. Four distinct elemental regimes are identified: acceptor-dopant, Sn-containing, BaZrO3-like, and BaCeO3-like. Acceptor-dopant configurations are best at forming oxygen vacancy defects and hydration relative to all other elemental regimes – consistent with experiments. A final filter related to the thermodynamic stability of CO2-containing conditions yields 43 promising configurations from the original 4793.

Rights

© 2023, Nicholas Alexander Szaro

Download

Share

COinS