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Mechanisms of sodiation in anatase TiO₂ in terms of equilibrium thermodynamics and kinetics.

ABSTRACT: Anatase TiO₂ is a promising anode material for sodium-ion batteries (SIBs). However, its sodium storage mechanisms in terms of crystal structure transformation during sodiation/de-sodiation processes are far from clear. Here, by analyzing the redox thermodynamics and kinetics under near-equilibrium states, we observe, for the first time, that upon Na-ion uptake, the anatase TiO₂ undergoes a phase transition and then an irreversible crystal structure disintegration. Additionally, unlike previous theoretical studies which investigate only the two end points of the sodiation process (i.e., TiO₂ and NaTiO₂), we study the progressive crystal structure changes of anatase TiO₂ upon step-by-step Na-ion uptake (Na _x TiO₂, x = 0.0625, 0.125, 0.25, 0.5, 0.75, and 1) for the first time. It is found that the anatase TiO₂ goes through a thermodynamically unstable intermediate phase (Na_0.25TiO₂) before reaching crystalline NaTiO₂, confirming the inevitable crystal structure disintegration during sodiation. These combined experimental and theoretical studies provide new insights into the sodium storage mechanisms of TiO₂ and are expected to provide useful information for further improving the performance of TiO₂-based anodes for SIB applications.

SUBMITTER: Tong Z

PROVIDER: S-EPMC9418246 | biostudies-literature | 2021 Aug

REPOSITORIES: biostudies-literature

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Mechanisms of sodiation in anatase TiO2 in terms of equilibrium thermodynamics and kinetics.

Tong Zhongqiu Z Kang Tianxing T Wu Jianming J Yang Rui R Wu Yan Y Lian Ruqian R Wang Hui H Tang Yongbing Y Lee Chun Sing CS

Nanoscale advances 20210625 16

Anatase TiO2 is a promising anode material for sodium-ion batteries (SIBs). However, its sodium storage mechanisms in terms of crystal structure transformation during sodiation/de-sodiation processes are far from clear. Here, by analyzing the redox thermodynamics and kinetics under near-equilibrium states, we observe, for the first time, that upon Na-ion uptake, the anatase TiO2 undergoes a phase transition and then an irreversible crystal structure disintegration. Addition ...[more]

PMID: 36134310

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Project description:BackgroundWe consider a focal adhesion to be made up of molecular complexes, each consisting of a ligand, an integrin molecule, and associated plaque proteins. Free energy changes drive the binding and unbinding of these complexes and thereby controls the focal adhesion's dynamic modes of growth, treadmilling and resorption.Principal findingsWe have identified a competition among four thermodynamic driving forces for focal adhesion dynamics: (i) the work done during the addition of a single molecular complex of a certain size, (ii) the chemical free energy change associated with the addition of a molecular complex, (iii) the elastic free energy change associated with deformation of focal adhesions and the cell membrane, and (iv) the work done on a molecular conformational change. We have developed a theoretical treatment of focal adhesion dynamics as a nonlinear rate process governed by a classical kinetic model. We also express the rates as being driven by out-of-equilibrium thermodynamic driving forces, and modulated by kinetics. The mechanisms governed by the above four effects allow focal adhesions to exhibit a rich variety of behavior without the need to introduce special constitutive assumptions for their response. For the reaction-limited case growth, treadmilling and resorption are all predicted by a very simple chemo-mechanical model. Treadmilling requires symmetry breaking between the ends of the focal adhesion, and is achieved by driving force (i) above. In contrast, depending on its numerical value (ii) causes symmetric growth, resorption or is neutral, (iii) causes symmetric resorption, and (iv) causes symmetric growth. These findings hold for a range of conditions: temporally-constant force or stress, and for spatially-uniform and non-uniform stress distribution over the FA. The symmetric growth mode dominates for temporally-constant stress, with a reduced treadmilling regime.SignificanceIn addition to explaining focal adhesion dynamics, this treatment can be coupled with models of cytoskeleton dynamics and contribute to the understanding of cell motility.

Project description:A sequence of chemical vapor synthesis and thermal annealing in defined gas atmospheres was used to prepare phase-pure anatase TiO2 nanocrystal powders featuring clean surfaces and a narrow particle size distribution with a median particle diameter of 14.5 ± 0.5 nm. Random networks of these nanocrystals were immobilized from aqueous dispersions onto conducting substrates and are introduced as model systems for electronic conductivity studies. Thermal annealing of the immobilized films at 100 °C < T < 450 °C in air was performed to generate particle-particle contacts upon virtual preservation of the structural properties of the nanoparticle films. The distribution of electrochemically active electronic states as well as the dependence of the electronic conductivity on the Fermi level position in the semiconductor films was studied in aqueous electrolytes in situ using electrochemical methods. An exponential distribution of surface states is observed to remain unchanged upon sintering. However, capacitive peaks corresponding to deep electron traps in the nanoparticle films shift positive on the potential scale evidencing an increase of the trapping energy upon progressive thermal annealing. These peaks are attributed to trap states at particle-particle interfaces in the random nanocrystal network (i.e., at grain boundaries). In the potential region, where the capacitive peaks are detected, we observe an exponential conductivity variation by up to 5 orders of magnitude. The potential range featuring the exponential conductivity variation shifts positive by up to 0.15 V when increasing the sintering temperature from 100 to 450 °C. Importantly, all films approach a potential- and sintering-temperature-independent maximum conductivity of ∼10-4 Ω-1·cm-1 at more negative potentials. On the basis of these results we introduce a qualitative model, which highlights the detrimental impact of electron traps located on particle-particle interfaces on the electronic conductivity in random semiconductor nanoparticle networks.

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Mechanisms of sodiation in anatase TiO₂ in terms of equilibrium thermodynamics and kinetics.

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Mechanisms of sodiation in anatase TiO<sub>2</sub> in terms of equilibrium thermodynamics and kinetics.

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