Diffusion Mechanisms of Radiolytic Species in Irradiated Al (Oxy-)Hydroxides

Journal Article · Tue Nov 27 00:00:00 EST 2018 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.8b07809· OSTI ID:1492310

Shen, Zhizhang  ^[1]; Ilton, Eugene S.  ^[1]; Prange, Micah P. ^[1]; Mundy, Christopher J.  ^[1]; Kerisit, Sebastien N.  ^[1]

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1. Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States

Rare-event simulations (climbing image nudge elastic band and metadynamics) were performed using density functional theory (DFT) and a hybrid exchange-correlation functional to elucidate and quantify the diffusion mechanisms of radiation-induced species (O^-, H⁰, and H₂) in boehmite (γ-AlOOH) and gibbsite (γ-Al(OH)₃). The two Al (oxy-)hydroxide phases are known to have much different radiolytic activities, but the underlying mechanisms remain unknown. The DFT calculations revealed that O^- diffusion occurred via proton-coupled hole transfer with high energy barriers in both phases. In contrast, energy barriers for H⁰ transfers were generally lower in boehmite than in gibbsite, suggesting a more facile diffusion in boehmite of H radicals to the surface, where H₂ formation can take place. Another key difference was the ability of H⁰ and H₂ to diffuse across the structural layers in gibbsite but not in boehmite. Therefore, while the formation of O and H radicals was energetically favored in gibbsite compared to boehmite, the DFT calculations indicated that the mechanisms of diffusion are responsible for the higher H₂ yields measured for boehmite compared to gibbsite

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1492310
• Report Number(s): PNNL-SA-136174
• Journal Information: Journal of Physical Chemistry. C, Vol. 122, Issue 50; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English