Characterizing Structure-Dependent TiS₂/Water Interfaces Using Deep-Neural-Network-Assisted Molecular Dynamics

LS Li and MFC Andrade and R Car and A Selloni and EA Carter, JOURNAL OF PHYSICAL CHEMISTRY C, 127, 9750-9758 (2023).

DOI: 10.1021/acs.jpcc.2c08581

Asa promising layered electrode material, TiS2-basedcapacitive deionization (CDI) devices for water desalination haveattracted significant attention. However, TiS2/H2O interfacial features, potentially important for device optimization,remain unidentified. Using Deep Potential Molecular Dynamics (DPMD),we characterized distinct aqueous interfaces introduced by four TiS2 terminations expected to be present as water intercalatesinto TiS2, namely, Armchair, Zigzag, Zigzag-L, and Zigzag-R.First, we assessed important representative physical properties ofthe system to validate the deep potentials (DPs). DPMD simulationsagree well with experiments and first-principles simulations, suggestingthe DPs are accurate and reliable. Subsequent simulations of theseTiS(2)/water interfaces revealed how TiS2 surfacetermination influences the structure of interfacial water. This effectis most evident in the first and second water layers close to theTiS(2) surface, and more pronounced when spontaneous dissociativeadsorption of water occurs. The extent of water dissociation on eachsurface was evaluated using enhanced sampling. Zigzag-L is the onlyinterface where proton transfer from adsorbed water to TiS2 surface S atoms is thermodynamically and kinetically favored. Thecoexistence of surface four-fold-coordinated Ti (Ti-4c)and one-fold-coordinated S (S-1c) is found to be essentialto making proton transfer feasible on the Zigzag-L surface. Furthermore,remaining unprotonated S-1c atoms can act as good protonacceptors after water dissociation. Thus, TiS2 with Zigzag-Ltermination may be a surface to avoid in CDI device construction,given that pH fluctuations adversely affect performance. This workprovides new understanding of TiS2/H2O interfacialfeatures that could aid future design and optimization of TiS2-based CDI devices for water desalination.

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