Abstract
Hydrogen titanates (HTOs) form a diverse group of metastable, layered titanium oxides with an interlayer containing both water molecules and structural protons. We investigated how the chemistry of this interlayer environment influenced electrochemical Li+-insertion in a series of HTOs, H2TiyO2y+1·nH2O (y = 3, 4, and 5). We correlated the electrochemical response with the physical and chemical properties of HTOs using operando X-ray diffraction, in situ differential electrochemical mass spectroscopy, solid-state proton nuclear magnetic resonance, and quasi-elastic neutron scattering. We found that the potential for the first reduction reaction trended with the relative acidity of the structural protons. This mechanism was supported with first-principles density functional theory (DFT) calculations. We propose that the electrochemical reaction involves reduction of the structural protons to yield hydrogen gas and formation of a lithiated hydrogen titanate (H2-xLixTiyO2y+1). The hydrogen gas is confined within the HTO lattice until the titanate structure expands upon subsequent oxidation. Our work has implications for the electrochemical behavior of insertion hosts containing hydrogen and structural water molecules, where hydrogen evolution is expected at potentials below the hydrogen reduction potential and in the absence of electrolyte proton donors. This behavior is an example of electrochemical electron transfer to a nonmetal element in a metal oxide host, in analogy to anion redox.
Original language | English |
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Pages (from-to) | 28795-28808 |
Number of pages | 14 |
Journal | Journal of the American Chemical Society |
Volume | 146 |
Issue number | 42 |
DOIs | |
State | Published - Oct 23 2024 |
Funding
We thank Dr. Michael A. Spencer for acquiring SEM images of the pristine materials in this study. We also thank Dr. Nicholas Strange, Dr. Johanna Weker, and Charles L. Troxel for their help with the operando XRD experiments at SSRL. This work was supported as part of the Fluid Interface Reactions, Structure and Transport (FIRST), an Energy Frontiers Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy. Experiments at ORNL\u2019s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for U.S. DOE under Contract No. DEAC05-00OR22725. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award # ECCS-2025064). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI). The solid-state NMR experiments were performed at the Ames National Laboratory, which is operated for the U.S. DOE by Iowa State University under contract # DE-AC02-07CH11358. S.F. acknowledges funding from the German Federal Ministry of Education and Research (BMBF) in the NanoMatFutur program (grant No. 03XP0423). S.F. and Z.J. acknowledge basic funding from the Helmholtz Association.