Tracking Atomic Diffusion in Surface and Bulk CuO via Neural Network-Based Molecular Dynamics

Abstract

Understanding the atomic diffusion process of a metal oxide helps with the design of more effective oxygen carriers for chemical looping with oxygen uncoupling (CLOU). Herein we investigated the atomic diffusion process in both slab and bulk CuO with varying oxygen vacancy (V O ) under CLOU conditions using density functional theory (DFT) calculations and molecular dynamic (MD) simulation based on the neural network (NN) potential. Although the diffusions of both the Cu and the O atoms are important for the slab model, the O atoms' outward diffusion to fill surface V O dominates the interlayer diffusion. In contrast, Cu atoms barely diffuse in the bulk model, and the diffusion process is dominated by O atoms through the V O . The MD-estimated chemical diffusion coefficients (10 −9 −10 −13 m 2 /s) and activation barriers (1.14−1.34 eV) of both models are consistent with those experimentally measured values. The diffusion coefficient increases with increasing V O , and the values of the slab model are two orders of magnitude higher than those of the bulk model with a similar V O . These results indicate that the chemical diffusion is dominated by the surface instead of the bulk, and the diffusion in the bulk only becomes important when it becomes the frontier of oxygen uncoupling, i.e., grain boundary between CuO and Cu 2 O. The majority of diffusion species (O atom or vacancy) and process revealed in this study provide atomic insight into the diffusion in CuO-based materials.

Enhancing Low-Potential Electrosynthesis of 2,5-Furandicarboxylic Acid on Monolithic CuO by Constructing Oxygen Vacancies

“…Figure A presents the high-resolution Cu 2p XPS profile of cp -CuO/CF and cpc -CuO/CF. As compared to that in cp -CuO/CF, the Cu 2+ peak in cpc -CuO/CF shifted to lower energy (Cu 2p 3/2 , from 933.8 to 933.4 eV; Cu 2p 1/2 , from 953.6 to 953.1 eV), implying more O V in cpc -CuO/CF. ,− As for the O 1s spectra in Figure B, the peaks centered at 529.7 and 529.5 eV were ascribed to the lattice oxygen species (O Latt ), while the peaks observed at 531.3 and 532.3–532.8 eV were attributed to the surface adsorbed oxygen species (O Ads ) and adsorbed H 2 O groups (O Water ). − Notably, the ratio of O Ads /O Latt over cpc -CuO/CF (3.80) was much higher than that of cp -CuO/CF (2.74), proving more surficial O V on cpc -CuO/CF (Table S2). Second, the EPR spectroscopy was used to validate the existence and relative content of O V in cpc -CuO/CF and cpc -CuO/CF.…”

“…Figure S9I showed the HR-TEM image of cp -CuO/CF, and the exposable crystal faces of CuO in cp -CuO/CF were (11̅1̅), (111), and (200), which was the same with that of cpc -CuO/CF, indicative of the negligible effect of CuO facets on FDCA production. Recently, the reported work showed that the activity of CuO could be modulated by its surficial O V . Along this line of thinking, we further examined the electronic states and surficial defects of CuO in both the cp -CuO/CF and cpc -CuO/CF.…”

“…Recently, the reported work showed that the activity of CuO could be modulated by its surficial O V . 43 Along this line of thinking, we further examined the electronic states and surficial defects of CuO in both the cp-CuO/CF and cpc-CuO/CF. XPS measurements were herein adopted.…”