Abstract
The solvation and transport of protons in aqueous solutions of phosphoric acid (PA), sulfuric acid (SA), and nitric acid (NA) were studied using ab initio molecular dynamics simulations. Systems with acid-to-water ratios of 1:1 and 1:3 were examined to understand the similarities and differences in transport mechanisms. The solvation structure of H3O+ in these systems is similar to that in slightly acidic water, with variations in the strength of hydrogen bonds (H-bonds) accepted by acid molecules. In aqueous PA systems, strong H-bonds between PA molecules are slightly affected by water, leading to significantly greater H3O+ diffusion compared to aqueous SA and NA systems. This enhanced diffusion is attributed to the participation of PA molecules in H3O+ transport, where the PA molecule can shuttle a proton for H3O+, facilitating a large displacement via collective proton hopping. This shuttling mechanism is prominent in aqueous PA but rare in aqueous SA and absent in aqueous NA. Moreover, the decomposition of H3O+ diffusion into vehicular and structural components indicates that the higher diffusion in aqueous PA is primarily due to the structural mechanism with the aid of PA molecules. In the aqueous NA systems, the vehicular diffusion is dominant at low water contents and the increase in water content improves the structural diffusion by forming connected H-bonds within water molecules. Our findings elucidate the role of acid molecules in proton transport within their aqueous solutions, thereby advancing the fundamental understanding of proton transport mechanisms.
Original language | English |
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Article number | 154504 |
Journal | Journal of Chemical Physics |
Volume | 161 |
Issue number | 15 |
DOIs | |
State | Published - Oct 21 2024 |
Funding
We thank Dr. Klaus-Dieter Kreuer (MPI-Stuttgart) for helpful discussions and insightful comments. We acknowledge support from the National Science Foundation awards Grant No. CHE-1764409. Computing resources were provided through an ACCESS allocation Grant No. DMR130078 on Stampede2 at the Texas Advanced Computing Center (TACC).
Funders | Funder number |
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Texas Advanced Computing Center | |
National Science Foundation | DMR130078, CHE-1764409 |