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Title: Structure and Dynamics of Aqueous Electrolytes Confined in 2D-TiO2/Ti3C2T2 MXene Heterostructures

Journal Article · · ACS Applied Materials and Interfaces
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [4];  [5]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Pennsylvania State Univ., University Park, PA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of California, Riverside, CA (United States)
  4. Tulane Univ., New Orleans, LA (United States)
  5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)

The synthesis of heterostructures of different two-dimensional (2D) materials offers an approach to combine advantages of different materials constituting the heterostructure and ultimately enhance their performance for applications such as electrochemical energy storage, achieving high energy, and high-power densities. Understanding the behavior of ions and solvents in confinement between these dissimilar layers is critical to understand their performance and control. Considering aqueous electrolytes, we explore the heterostructure of 2D lepidocrocite-type TiO2 (2D-TiO2) and hydroxylated or O-terminated Ti3C2 MXene using ReaxFF molecular dynamics simulations and elastic/quasielastic neutron scattering techniques. Simulating a bilayer water intercalation, we find that the extent of interlayer hydration is impacted most by the surface terminations on the MXene and is marginally affected by 2D-TiO2. However, the introduction of 2D-TiO2 decreases the water self-diffusion due to the notch sites (i.e., surface oxygen ridges) entrapping water molecules. Intercalating alkali cations into the heterostructures, we find that Li+ is predominantly adsorbed at the 2D-TiO2 surface instead of the MXenes with the preferential occupation of the notch sites. In contrast, Na+ forms a planar solvation with water, while K+ is adsorbed both at the O-terminated MXene and 2D-TiO2. This behavior is altered when OH-terminated MXene is involved—the repulsion from the protons on the MXene surface forces the K+ ions to be adsorbed exclusively to 2D-TiO2, while Na+ retains some of its solvation in the water layer due to its smaller size. In OH-terminated MXenes, we see a consistent transfer of protons from the MXene surface toward 2D-TiO2, implying a greater capacity to store protons in the heterostructures. Of the three cations simulated, Na+ hinders the proton migration the least and Li+ the most because of its position near the 2D-TiO2 surface. Furthermore, 2D-TiO2/MXene heterostructures are likely to exhibit a higher energy density but lower power density, especially with Na+ intercalation.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1824958
Journal Information:
ACS Applied Materials and Interfaces, Vol. 12, Issue 52; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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