Neat liquid phosphoric acid (H(3)PO(4)) has the highest intrinsic proton conductivity of any known substance and is a useful model for understanding proton transport in other phosphate-based systems in biology and clean energy technologies. Here, we present an ab initio molecular dynamics study that reveals, for the first time, the microscopic mechanism of this high proton conductivity. Anomalously fast proton transport in hydrogen-bonded systems involves a structural diffusion mechanism in which intramolecular proton transfer is driven by specific hydrogen bond rearrangements in the surrounding environment. Aqueous media transport excess charge defects through local hydrogen bond rearrangements that drive individual proton transfer reactions. In contrast, strong, polarizable hydrogen bonds in phosphoric acid produce coupled proton motion and a pronounced protic dielectric response of the medium, leading to the formation of extended, polarized hydrogen-bonded chains. The interplay between these chains and a frustrated hydrogen-bond network gives rise to the high proton conductivity.

AMP and its blends are an attractive solvent for CO2 capture, but the underlying reaction mechanisms still remain uncertain. We attempt to elucidate the factors enhancing bicarbonate production in aqueous AMP as compared to MEA which, like most other primary amines, preferentially forms carbamate. According to our predicted reaction energies, AMP and MEA exhibit similar thermodynamic favorability for bicarbonate versus carbamate formation; moreover, the conversion of carbamate to bicarbonate also does not appear more favorable kinetically in aqueous AMP compared to MEA. Ab initio molecular dynamics simulations, however, demonstrate that bicarbonate formation tends to be kinetically more probable in aqueous AMP while carbamate is more likely to form in aqueous MEA. Analysis of the solvation structure and dynamics shows that the enhanced interaction between N and H2O may hinder CO2 accessibility while facilitating the AMP + H2O → AMPH(+) + OH(-) reaction, relative to the MEA case. This study highlights the importance of not only thermodynamic but also kinetic factors in describing CO2 capture by aqueous amines.

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Electrolyte and electrode materials used in lithium-ion batteries have been studied separately to a great extent, however the structural and dynamical properties of the electrolyte-electrode interface still remain largely unexplored despite its critical role in governing battery performance. Using molecular dynamics simulations, we examine the structural reorganization of solvent molecules (cyclic ethylene carbonate : linear dimethyl carbonate 1 : 1 molar ratio doped with 1 M LiPF) in the vicinity of graphite electrodes with varying surface charge densities (σ). The interfacial structure is found to be sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. We also evaluated the potential difference across the electrolyte-electrode interface, which exhibits a nearly linear variation with respect to σ up until the onset of Li ion accumulation onto the graphite edges from the electrolyte. In addition, well-tempered metadynamics simulations are employed to predict the free-energy barriers to Li ion transport through the relatively dense interfacial layer, along with analysis of the Li solvation sheath structure. Quantitative analysis of the molecular arrangements at the electrolyte-electrode interface will help better understand and describe electrolyte decomposition, especially in the early stages of solid-electrolyte-interphase (SEI) formation. Moreover, the computational framework presented in this work offers a means to explore the effects of solvent composition, electrode surface modification, and operating temperature on the interfacial structure and properties, which may further assist in efforts to engineer the electrolyte-electrode interface leading to a SEI layer that optimizes battery performance.