Ab initio evaluation of oxygen diffusivity in LaFeO 3 : the role of lanthanum vacancies
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esearch Letters
Ab initio evaluation of oxygen diffusivity in LaFeO3: the role of lanthanum vacancies Andrew M. Ritzmann, Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544 Ana B. Muñoz-García and Michele Pavone, Department of Chemical Sciences, University of Naples Federico II, Naples 80126, Italy John A. Keith, Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 Emily A. Carter, Department of Mechanical and Aerospace Engineering, Program in Applied and Computational Mathematics, and Andlinger Center for Energy and Environment, Princeton University, Princeton, New Jersey 08544 Address all correspondence to Emily A. Carter at [email protected] (Received 9 May 2013; accepted 29 July 2013)
Abstract Solid oxide fuel cells (SOFCs) are attractive for clean and efficient electricity generation, but high operating temperatures (Top > 800 °C) limit their widespread usage. Oxygen ion conducting cathode materials (mixed ion-electron conductors, MIECs), such as La1−xSrxCo1−yFeyO3 (LSCF), enable lower Top by reducing cathode polarization losses. Understanding how composition affects oxygen diffusion in LaFeO3 is vitally important for designing high-performance LSCF cathodes. To do this, we employ first-principles density functional theory plus U (DFT+U) calculations to show how lanthanum vacancies in LaFeO3 dramatically change the oxygen diffusion coefficient. Our ab initio results show that A-site substoichiometry is a viable route to increased oxygen diffusion and higher SOFC performance.
Resource scarcity, energy security, and anthropogenic environmental change necessitate new technologies for sustainable electricity production. Solid oxide fuel cells (SOFCs) meet this challenge by efficiently and cleanly generating electrical power using electrochemistry.[1] Unfortunately, high cathode overpotentials cause voltage losses that hinder the widespread use of SOFC devices.[2] High operating temperatures (Top > 800 °C) can offset slow cathode kinetics to obtain useful power densities, but high Top detrimentally leads to short cell lifetimes[3] and requires high energy input, long start-up times, and expensive interconnect materials (e.g. La1−xSrxCrO3).[4] Therefore, developing cathode materials that facilitate faster kinetics will enable intermediate Top (600–800 °C), leading to more efficient devices, longer cell lifetimes, and lower material costs. Recently proposed cathode materials such as La1−xSrxCo1−yFeyO3 (LSCF), Sr2Fe2−xMoxO6 (SFMO) and Ba1−xSrxCo1−yFeyO3 (BSCF) successfully enable intermediate temperature operation.[5] The works of Adler[2] and Kuklja et al.[6] offer broad perspectives on the different processes governing oxygen reduction at SOFC cathodes. Mixed ion-electron conducting (MIEC) capability, defined by bulk oxygen ion and electron conduction, enables these promising cathode materials to operate at reduced temperatures. Allowing oxygen diffusion through the cathode increases the active areas[7] for these materials
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