Defect-Induced Phenomena in Perovskites under Realistic External Conditions (DEFTD)
Eugene A. Kotomin
Department of Physical Chemistry of Solids, Max-Planck Institute for Solid State Research, Stuttgart (Germany)
Local Project ID:
HPC Platform used:
Hazel Hen of HLRS
Fuel cells and batteries are expected to play very important roles in future energy supply. While ambient-temperature fuel cells transforming chemical energy into electricity suffer from sluggish kinetics, high temperature (>800 °C) fuel cells suffer from limited long-term stability. Fuel cells operating at 250-500°C with ceramic proton-conducting oxide electrolytes (H-SOFC) promise the desired compromise between cost, rapid start-up time and stability because H-SOFCs (i) can fast reach the operating temperature; (ii) do not require noble metals for electrodes; and (iii) do not have materials problems typical for high temperature cells.
Materials for the solid electrolyte, the heart of H-SOFC, and for anodes are relatively well established. However, finding an efficient cathode material still poses a problem because the cathode reaction becomes the rate limiting factor. In currently used cathode materials and composites, oxygen reduction is believed to be restricted to three-phase contacts, leading to insufficient current density. Finding a stable p-type conductor with sufficient proton conductivity would provide such efficient cathode materials and pave the way to large scale application of H-SOFC.
Our project is focused on massive parallel computer modeling of new prospective perovskite materials for the fuel cells from first principles. This requires calculations of the atomic, electronic, and magnetic properties without any a priori assumptions, so called ab initio or first principles. Understanding of a role of dopants and defects is a key to predict the improvement of device performance which is validated later on experimentally.
Typical materials are ABO3 type perovskites and solid solutions, e.g. (La,Sr)(Co,Fe)O3. Addressing realistic operational conditions is achieved via combination with ab initio thermodynamics. The accurate state of the art first principles calculations of large supercells with low symmetry are very time consuming and need use of supercomputing technologies as provided in particular by the High-Performance Computing Center Stuttgart (HLRS). We used primarily the CRAY XC40 system (Hazel Hen) with several thousand cores used in defect calculations. Primarily, the massive parallel computer codes VASP and CRYSTAL were employed.
In our theoretical modelling, we identified the rate determining step of the oxygen reduction reaction on cathode surfaces, the optimal cathode terminations, and reasons why oxygen transport is so efficient in BSCF material.
The planned insight into the proton uptake and proton migration process in ferrates and cobaltates could greatly promote development of more efficient cathode materials for intermediate-temperature fuel cells based on proton-conducting oxide electrolytes. Exploring new solid materials as fast ion conductor electrolytes to produce high performance all-solid-state batteries is an active field of research. In this project, using ab initio-based calculations, we investigate also the mechanism of ionic conductivity and superionic behavior in three promising solid electrolytes for batteries, namely Li2Sn2S5, LiSCN and NaSCN. All these materials are expected to behave as superionic conductors at elevated temperatures.
We use density functional theory (DFT) calculations for finding the ground state atomic and electronic structures, mechanisms and values of ionic conductivity and superionic phase transition temperature. We will then compare our theoretical results with the findings of our experimental collaborators in Max-Planck Institute for Solid State Research and provide atomistic insight into the transport properties in these materials which will be very helpful to shed light on experimental observations.
The results of our research were published in leading chemical and physical journals.
Publications supported by DEFTD project (2013-2020)
Institute of Solid State Physics, University of Latvia, Riga, Latvia
Prof. Dr. Eugene A. Kotomin
Max Planck Institute for Solid State Research
Physical Chemistry of Solids (Joachim Maier)
Heisenbergstraße 1, D-70569 Stuttgart (Germany)
e-mail: E.Kotomin [@] fkf.mpg.de
Physical Chemistry of Solids (Joachim Maier)
HLRS Project ID: DEFTD
update: March 2020