First-Principles Multiscale Diffusion Kinetics Modeling for Oxygen Carrier Reduction in Chemical Looping

Abstract

Ion diffusion within materials is a critical yet often rate-limiting phenomenon during carbon-free energy storage and release. A theoretical paradigm of diffusion kinetics is introduced, and the reduction kinetics of hematite oxygen carrier by hydrogen in chemical looping is studied as a case. The migration pathway of oxygen-vacancy diffusion in the bulk is searched by density functional theory and transition state theory, and the phonon spectra of the initial, final, and transition states are calculated. Based on a newly developed bulk parcel model, the apparent diffusivity is obtained. Coupling it into the microkinetic model, the reduction rate could be predicted, and experimental results validate its accuracy. So far, all kinetic constants in the microkinetic model can be predicted in silico, which helps to bridge the gap between microscopic mechanism and macroscopic observation. The framework is promising for facilitating further understanding of noncatalytic gas–solid reaction kinetics and accelerating energy material design.