Screening dual variable-valence metal oxides doped calcium-based material for calcium looping thermochemical energy storage and CO2 capture with DFT calculation

Abstract

The reaction characteristics of calcium-based materials during calcium looping (CaL) process are pivotal in the efficiency of CaL thermochemical energy storage (TCES) and CO₂ capture systems. Currently, metal oxide doping is the primary method to enhance the reaction characteristics of calcium-based materials over multiple cycles. In particular, co-doping with variable-valence metal oxides (VVMOs) can effectively increase the oxygen vacancy content in calcium-based materials, significantly improving their cyclic reaction characteristics. However, there are so numerous VVMOs co-doping schemes that the experimental screening process is complex, consuming considerable time and economic costs. Density functional theory (DFT) calculations have been widely used to reveal the impact of metal oxide doping on the cyclic reaction characteristics of calcium-based materials, with calculation results showing good agreement with experimental conclusions. Nevertheless, there is still a lack of research on utilizing DFT to screen calcium-based materials, and a systematic research methodology has not yet been established. In this study, a systematic DFT-based screening methodology for calcium-based materials was proposed. A series of key parameters for DFT calculations including CO₂ adsorption energy, oxygen vacancy formation energy, and sintering resistance were proposed. Furthermore, a preliminary mathematical model to predict the CaL TCES and CO₂ capture performance of calcium-based materials was introduced. The aforementioned DFT method was employed to screen for VVMOs co-doped calcium-based materials. The results revealed that Mn and Ce co-doped calcium-based materials exhibited superior DFT-predicted reaction characteristics. These DFT predictions were validated through experimental assessments of cyclic thermochemical energy storage, CO₂ capture, and relevant characterization. The outcomes demonstrate a high degree of consistency among DFT-based predictions, experimental results, and characterization. Hence, the DFT-based screening methodology for calcium-based materials proposed herein is a viable solution, poised to offer theoretical insights for the efficient design of calcium-based materials.