Computational Investigations of the Water Structure at the α-Al<sub>2</sub>O<sub>3</sub>(0001)–Water Interface

Zhang, Xiaoliu; Arges, Christopher G.; Kumar, Revati

doi:10.1021/acs.jpcc.3c03243

Cited by 5 publications

(2 citation statements)

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“…The surface undergoes several reactive events such as epoxide opening and alkoxide shuttling as well as proton abstraction (Figure ). , These techniques were further extended to another potential water dissociation electrocatalyst α-Al 2 O 3 (001)–water interface . Finally, we have also contributed to the development of machine learning toolsfrom neural network-based force fields that can effectively increase the spatial and temporal scales of AIMD to algorithms that can connect properties from molecular simulations to IEM properties, such as activity coefficients, to potentially fill gaps in our understanding of ion partitioning behavior with IEMs. , Our future work will extend our machine learning capabilities to BPMs in various electrochemical systems.…”

Section: The Authors’ Contributions To the Field Of Bpmsmentioning

confidence: 99%

“…Apart from trimethylamine and the GO sheet, the water splitting and proton transfer mechanism catalyzed by metal oxide, − poly(ethylene glycol), functionalized polyester, and metal–organic frameworks (MOFs) were investigated via ab initio and force-field-based reactive molecular dynamics as well, giving rise to a more detailed view of the mechanism of catalyzed water splitting in BPMs. However, it should be mentioned that these investigations have been limited by the significant computational expense associated with MD simulations at the DFT level, which resulted in nonergodic dissociation behaviors at the interface.…”

Section: Computational Investigation Of Water Dissociation and Associ...mentioning

confidence: 99%

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ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

Kulkarni,

Yang,

Zhang

et al. 2024

ACS Appl. Energy Mater.

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Sustainable energy conversion, chemical manufacturing, and separations are central to addressing the world's energy and environmental challenges. Electrochemical platforms stand as a cornerstone in addressing these challenges because they are low exergy and can be powered on renewable electrons. In electrochemical systems, bipolar membranes (BPMs) are emerging as a unique class of ion exchange membranes poised to revolutionize various electrochemical processes via pH control of anode and cathode chambers and in situ pH adjustment. In this Spotlight Review, we provide a comprehensive review of electrochemical platforms utilizing BPMs for energy conversion (water electrolyzers for hydrogen production, fuel cells, and flow batteries), chemical manufacturing (electrolyzers that convert carbon dioxide into value-added chemicals and nitrate into ammonia), and separations. The motivation for using BPMs, as well as their performance and durability, in electrochemical platforms are disseminated. We also discuss current challenges that impede BPM electrochemical systems from competing with state-of-the-art electrochemical systems using monopolar ion-exchange membranes (e.g., anion/hydroxide exchange membranes and cation/proton exchange membranes). The review also covers molecular modeling and continuum modeling efforts to understand the basic mechanisms that govern BPM performance.

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Section: The Authors’ Contributions To the Field Of Bpmsmentioning

confidence: 99%

Section: Computational Investigation Of Water Dissociation and Associ...mentioning

confidence: 99%

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

Kulkarni,

Yang,

Zhang

et al. 2024

ACS Appl. Energy Mater.

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From Graphene Oxide to Graphene: Changes in Interfacial Water Structure and Reactivity Using Deep Neural Network Force Fields

Azom,

Milet,

David

et al. 2024

J. Phys. Chem. C

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Graphene oxides (GO) are thin graphene sheets containing oxygen-bearing defects. These sheets have a complex structure with sp 3 carbons interspersed among sp 2 carbons, which results in competition between aromatic and hydrophilic domains at the GO−water interface. The GO−water as well as neat graphene−water interfacial regions play a crucial role in various applications. While ab initio molecular dynamics simulations provide high accuracy in studying this complex region, they require significant computational resources, which limits the investigation of the interface at both time and length scales. To tackle this issue, a deep neural network force field (DNNF), trained and validated on AIMD data, was developed. It achieves DFT-level accuracy using only a fraction of the computational cost. This DNNF has been successfully used for simulating graphene oxide to reduced graphene oxide right up to fully reduced graphene−water interfaces. The ordering of water near the interface was studied as a function of oxidation level from fully oxidized graphene oxide to graphene. The vibrational sum frequency generation spectrum of the graphene−water interface was determined and compared to experimental data as well as spectra from graphene oxide−water sheets at different oxidation levels. Connections between different spectral signatures and the orientation of different waters were determined. The reactivity and buckling of the different sheets were examined. The analyses of the trajectories revealed the formation of multiple hydronium formation events with sustained proton hopping over more than a 100 ps in the fully oxidized GO−water systems.

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ReaxFF Study of Surface Chemical Reactions between α-Al₂O₃ Substrates and H₂O/H₂ Gas-Phase Molecules

Zhang,

Nayir,

Shin

et al. 2024

J. Phys. Chem. C

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We developed an Al/O/H ReaxFF force field to explore chemical reactions on α-Al 2 O 3 surfaces in H 2 O/H 2 gas-phase environments. This force field generates surface energy profiles of A-, C-, R-, and M-planes with various terminations (Al-or O-) and predicts the thermodynamic and kinetic behaviors of hydrolysis on Al-terminated α-Al 2 O 3 (0001), consistent with quantum chemical studies. Molecular dynamics (MD) simulations of H 2 O/α-Al 2 O 3 (0001) reveal that water autocatalysis plays a significant role in accelerating H 2 O dissociations on Alterminated α-Al 2 O 3 (0001). Compared with the 50% Al-terminated surface, the 100% Alterminated surface becomes more easily hydroxylated at temperatures as low as 350 K, relying more on an O x H y clustering mechanism than complete H 2 O dissociations, and desorbs significantly more H 2 O molecules once heated up to 500 K or higher. But heating cannot eliminate surface hydroxyls for either case, and achieving a Gibbsite-like surface by H 2 O exposure is unlikely. H 2 O dissociations on α-Al 2 O 3 (0001) terminated with randomly distributed surface Al species deviate from 1−2 and 1−4 pathways due to irregular vacancy defects, and a random surface appears to be more reactive to H 2 O than the ordered one with the same surface Al coverage. Simulations of H 2 /α-Al 2 O 3 suggest that the combination of a dense surface O coverage and a low thermodynamic surface stability leads to elevated H 2 dissociation kinetics. To accelerate the surface O removals of 100% O-terminated α-Al 2 O 3 (0001) in H 2 gas exposure, we reduced the H−H σ bond energy parameter, equivalent to lowering the H 2 dissociation barrier by ∼ 19.4 kcal/mol during the simulation. After ∼ 1.5 ns, the surface termination became comparable to the 100% Al-terminated one but retained a small quantity of hydroxyls. This force field reveals how the α-Al 2 O 3 crystallographic plane and the surface termination influence the dissociation behaviors of H 2 O/H 2 gas molecules and lays the foundation for future force field developments targeted at thin film epitaxy on sapphire.

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Computational Investigations of the Water Structure at the α-Al₂O₃(0001)–Water Interface

Cited by 5 publications

References 76 publications

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

From Graphene Oxide to Graphene: Changes in Interfacial Water Structure and Reactivity Using Deep Neural Network Force Fields

ReaxFF Study of Surface Chemical Reactions between α-Al₂O₃ Substrates and H₂O/H₂ Gas-Phase Molecules

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Computational Investigations of the Water Structure at the α-Al2O3(0001)–Water Interface

Cited by 5 publications

References 76 publications

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

From Graphene Oxide to Graphene: Changes in Interfacial Water Structure and Reactivity Using Deep Neural Network Force Fields

ReaxFF Study of Surface Chemical Reactions between α-Al2O3 Substrates and H2O/H2 Gas-Phase Molecules

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Product

Resources

About

Computational Investigations of the Water Structure at the α-Al₂O₃(0001)–Water Interface

ReaxFF Study of Surface Chemical Reactions between α-Al₂O₃ Substrates and H₂O/H₂ Gas-Phase Molecules