Storage and Conversion Applications

Brief Overview and Motivation

Introduction

Ion Solvation and Transport at Bulk and Electrified Interfaces for

It explains the turnover behavior in the generated 𝐼𝑆𝐶 or𝑉𝑂𝐶 as a function of the nanolayer thickness. The surface potential of the water-vapor interface from classical simulations." In: The Journal of Physical Chemistry B pp.

Facilitated Lithium-Ion Transport in Ionic Liquid Functionalized

Abstract

The result suggests that the morphological properties of ion aggregates and ion conduction are crucial in determining ion conductivity at high salt concentrations, which must be taken into account when designing such a mixed-conductive polymer. The author participated in performing simulations of amorphous polymers, discussing the results of ion solvation and transport in the polymers, and preparing a draft.

Introduction

Conjugated polymers with ionic liquid-like side chains hold considerable promise in solvent-free mixed conduction. Ionic conductivity in polymer electrolytes is dependent on the concentration and mobility of ions, which are related to the polarity and segmental dynamics of the polymer.

Computational Methods

In this case, ionic mobility is related to the extent to which the aggregates form continuous domains throughout the material. In addition, equal numbers of Li+ and BF4− ions were added at random positions in the simulation box to study the effects of salt concentration.

Figure 3.1: MD snapshots for the crystalline polymers at 𝑟 = 0 . 2 (left) and 𝑟 = 0 . 8 (right)

Results and Discussion

Addition of salt to the simulation allows detailed characterization of the solvation environment for both Li+ and BF4− in the polymer (Fig. 3.4). Li-BF4 contact time in (a) amorphous and (b) crystalline polymers. c) Calculated diffusion coefficients for Li+ and BF4− as a function of salt concentration in the amorphous (solid symbols) and crystalline polymer (open symbols).

Figure 3.2: Chemical structure and structural characterization of P3HT-IM. (a) Schematic structure of the thiophene-based conjugated polymeric ionic liquid used in this study

Conclusion

This suggests that the ion transport mechanism in P3HT-IM deviates from that of standard ion-conducting polymers and further supports the formation of a percolating ionic network as the primary mechanism for ion transport. Furthermore, ion diffusivities from both MD simulations and PFG NMR measurement indicate a lithium transfer number of approximately 0.5, supporting that the percolated solvation network promotes lithium transport in a manner unique to many ion-conducting polymers where ion transport is strongly coupled to polymer segmental dynamics.

Appendix

To calculate the 𝛿 𝐸anode in the presence of constant potential electrodes, the approach of Ref. Effects of Polymer Coatings on Electrolytically Deposited Lithium Metal.” In: Journal of the American Chemical Society, p.

Figure 3.8: Mean-square displacement of ions in the amorphous (left column) and the crystalline (right column) polymers at several salt concentrations.

Lithium-Ion Transport in Polyborane-based electrolytes

Abstract

In this chapter, we discuss the mechanism of ion transport in recently developed polyborane-based electrolytes that use the formation of a spatially extended ionic network to facilitate lithium ion transport. Here, as a proof of concept, we discuss simulation results of the lithium ion conduction mechanism in butylated polydiethylboranes (poly-b2EtB) at different salt concentrations.

Introduction

In this chapter, the mechanism of ionic conductivity in a new, monoionically conductive electrolyte based on polyborane is presented. The conductivity measured by EIS follows an Arrhenius temperature dependence, suggesting that the ionic conductivity is decoupled from the segmental relaxation of the polyborane-based electrolytes.

Simulation Model and Method

All transport properties reported here were averaged using simulation trajectories over at least 80 ns after an equilibrium of at least 20 ns.

Results and Discussion

Here, we discuss the transport of lithium ions through the formation of an ionic network, decoupled from the segmental dynamics of the polymer. The partner exchange mechanism further accelerates long-range lithium-ion transport in a large array that provides more connectivity.

Table 4.1: Fitting results of ionic conductivity ( 𝜎 ) in Fig. 4.2 using the Arrhenius relation: 𝜎 ( 𝑇 ) = 𝜎 0 exp − 𝐸 𝑎 / 𝑅𝑇

Conclusion

6.7) electrode polarizations for F−SAM intercalation (top) and deintercalation (bottom) in different SAM layers. Challenges and Prospects of the Role of Solid Electrolytes in the Revitalization of Lithium Metal Batteries.” In: Journal of Materials Chemistry A4 (2016), pp.

Interfacial Ion Solvation and Electron Transfer in Solid Electrolyte

Abstract

In this chapter we investigate the electron transfer to lithium ions at the interface between a platinum metal anode and a solid polymer electrolyte, as a chemically and structurally well-defined model for redox processes in the solid electrolyte interphase of battery electrodes. Atomic resolution simulations are performed with constant potential polarizable electrodes to characterize the interfacial kinetics of electron transfer, including lithium ion solvation structures and solvent reorganization effects as a function of the applied electrode potential.

Introduction

However, relatively little is known about ion solvation and electron transfer (ET) in the SEI, which is complicated by the intrinsic heterogeneity and complexity of this material. Associated liquid ether electrolytes, 1,2-dimethoxyethane (DME) and tetraglyme (G4), are also examined to investigate the extent to which polymerization alters local monomer interactions with respect to properties relevant to electron transfer.

Figure 5.1: Chemical structures of the ethereal molecular electrolytes (DME and G4) and polymer electrolytes (PEO and P(2EO-MO)).

Methods and Calculation Details

Second, electrode atoms are introduced at both ends of the simulation cell in the z direction, without any overlap. Electrode atoms are fixed in space according to the mean of the Gaussian distribution.

Results and Discussion

The first solvation shell of the lithium ion contains 5 or 6 ether oxygen atoms of PEO which is the only chemical moiety that preferentially interacts with lithium ions [190, 191]. However, for P(2EO-MO) the fraction of single-chain solvation decreases, and for G4 the fraction of single-chain solvation increases significantly in the vicinity of the anode.

Figure 5.3: Lithium-ion coordination environment at infinite dilution. Index of oxygens of (a) bulk PEO and (b) bulk P(2EO-MO) that forms the first solvation shell of a representative lithium-ion

Conclusions

Simulations show that all considered electrolytes except DME provide a solvent separation layer for Li + ions at the anode interface with both one-chain and two-chain solvation environments. However, at the highest bias potential, the DME allows direct contact between the Li+ ions and the anode with greater propensity.

Appendix

Molecular dynamics simulation studies of the structure of a mixed carbonate/LiPF6 electrolyte near the graphite surface as a function of electrode potential.” In: The Journal of Physical Chemistry C p. Evaluation of the constant potential method in the simulation of electrical double-layer capacitors.” In: Journal of Chemical Physics 141.18 (November 2014), p.

Figure 5.9: Mean electric potential across the simulation cell for the various elec- elec-trolytes and bias potentials

Design Rules for Passivating Self-Assembled Monolayers to a

Abstract

The solvation structure of SAM fluoride ions suggests that a functional SAM molecule must contain both fluorinated and ether moieties to allow efficient movement of F- between the bulk electrolyte and the metal electrode. The structure–dynamics relationship in SAM solvation of the fluoride ion was found to reveal the important role of the free energy barrier found in the F−SAM solvation structure.

Introduction

We perform all-atom simulations with polarizable metal electrodes coated with a SAM layer to investigate the structure and solvation dynamics of fluoride ions. The SAM fluoride ion solvation structure suggests that a functional SAM molecule must have both fluorinated and ether moieties to enable facile F-shuttle between the bulk electrolyte and the metal electrode.

Methods and Calculation Details

In Here, 𝑙SAM=1.2 nm is used for all SAM molecules according to the average position of the end group (CF3).

Results and Discussion

To rank SAM molecules according to F− SAM (de)interaction kinetics, the F−SAM (de)interaction relaxation times obtained by Eqs. This softened the relaxation time ¯𝑄(𝑡) (Figure 6.8), confirming that the surprisingly fast kinetics is an artifact of the SAM region selection.

Figure 6.3: Fluoride-ion SAM density with bias potential (ΔΨ = 4 V) for various SAM layers

Summary and Conclusions

We could further explore some connections between equilibrium fluctuation of electrode charge polarization and non-equilibrium relaxation [50] to test the robustness of the assumptions of linear-response theory at a SAM/metal interface. We could explore the connections between the structural information from the SAM solvation sites and their dynamic behavior, as we find here a tentative structure–dynamics relationship in F−SAM solvation.

Appendix

We begin with an analysis of the fluoride-ion solution envelope, consisting of BTFE molecules, co-solvent molecules and Np+1 ions. Thus, we conclude that the trends observed experimentally reflect a delicate balance between factors caused by co-solvents.

Figure 6.8: Kinetics of the electrode polarization during F − SAM (de-)intercalation.

Energy Transduction of Water Kinetic Energy to Electricity using

The relatively low resistance of the nickel nanolayers leads to the lowest peak power among the metal nanolayers we considered. Molecular hydrophobicity at a macroscopically hydrophilic surface." In: Proceedings of the National Academy of Sciences pp.

Generating Electricity Using Metal Nanolayers from a Flow of

Abstract

It turns out that the metal nanolayers induce electric current with a linear current of salt gradients in addition to flowing water droplets over the nanolayers or with an oscillating current with a constant salinity. As efficient as other hydrovoltaic transducers, our heterostructured metal nanolayers suggest additional design rules, including electron transfer within their thermal oxide nanooverlayer terminating the metal and good nanoconfinement for electron transfer within the metal beneath.

Introduction

Interestingly, in addition to the passivation of the metal below, we find a prominent role for the thermal oxide nano-overlay, whose redox activity strongly affects the energy conversion performance. More interestingly, the energy conversion is highly sensitive to the thickness of the metal substrate and exhibits an optimal thickness corresponding to the free electron mean path.

Simulation Method

Interactions between atoms in the nanolayer and other atoms in the simulation cell are described using both electrostatic and Lennard-Jones (LJ) interactions. Oxide-like atoms in the nanolayer are uncharged, while the charges of the nanolayer's metallic atoms are allowed to fluctuate in response to charges in the solution.

Table 7.1: Lennard-Jones parameters for water, ions, and nanolayer atom.

Design Rules Found in Experiments

This effect of redox activity of the oxide upper layer provides evidence that intra-oxide electron transfer [203] between M𝑚+ and M𝑛+ occurs. The volcano-type thickness effect suggests that film thickness on the order of the electron mean free path [51] improves current generation, providing a nano-constraint on electron flow in a metal substrate.

Figure 7.1: Experimental results of energy conversion using metal nanolayers with a flow of alternating salinity

Computational Results and Discussion

On the other hand, the short-circuit current (I𝑆𝐶) with zero external current connected to the transducer depends not only on The second design rule suggests that the redox activity of the oxide layer significantly increases the capacitance.

Conclusion

When the dynamics of the salinity boundary are on the same time scale as the flow dynamics, the result is a spike-like flow as in the experiment. When the time scales of salinity boundary and flow dynamics are similar, the time series of current output becomes peak-like.

Appendix

Rough and diffuse layer interactions during ionic strength cycling. In: The Journal of Physical Chemistry C pp. Adsorption of charged ions only at the hydroxylated (0001) 𝛼-quartz/water interface.” In: The Journal of Physical Chemistry C pp.

Figure 7.2: Model of charge mobility in nanoconfined, insulator-terminated metal conductor

Energy Conversion using Metal Nanolayers in a Wave Tank

Abstract

The energy conversion is made possible by ion adsorption and desorption at a moving air-water interface, together with wave action, which then induces electrons into the metal. Additional factors, including metallic elements and substrate, are also explored to optimize energy conversion efficiency.

Introduction

Their scalable nature and ease of fabrication make these metal nanolayers attractive, cost-effective alternatives for open ocean wave energy harvesting applications. Using both experiments and model calculations, we discuss mechanisms for electricity generation at an air:water interface in wave tank operation, and provide guiding principles for scaling up the operations of hydrovoltaic metal nanolayers.

Calculation Methods

The strength of the external electric field is different for different regions, either in equilibrium or out of equilibrium. The non-zero electric field (𝐸𝑒𝑥 𝑡 = −𝑄𝑖 𝑜𝑛 . 𝜖0 ) is applied only to the 3 nm long upper region of the metal (one fifth of its height) and the rest of the metal is under a zero electric field .

Results and Discussion

The amount of charge transferred (𝑄net) in the wetting phase is an important indicator for evaluating the performance of metal nanosheets. This result was surprising, as after 24 h in the wave tank we observed little or no visual degradation of either nanosheet on either substrate.

Figure 8.2: Electrical outputs in experiment and in computation. (a) Electrical outputs via a 10 nm Ni nanolayer on glass connected in series to a 100 Ω external resistor in our Instant Ocean wavetank

Conclusion

Unlike the nickel nanolayers on glass, the nanolayers on PET produced negligible power after 24 hours in the tank. The scalability with the nanolayers' width remains in question due to the limited accessibility to the nanolayers' surface in this study.

Appendix

Ion Pairing in Molecular Simulations of Aqueous Alkali Halide Solutions.” In: The Journal of Physical Chemistry B pp. United atom description for ethers, glycols, ketones and aldehydes. In: The Journal of Physical Chemistry B pp.

Figure 8.9: Triplicate electrical outputs of 10 nm Ni nanolayers in our Instant Ocean wavetank deposited via PVD in the same batch on glass substrate

Coupled and Decoupled Dynamics of Stern and Diffuse Layers

Abstract

Heterodyne-detected second harmonic generation (HD-SHG) measurements, which provide disentangled electrical double-layer (EDL) information, show that the dynamics in the Stern and diffuse layers are decoupled from each other under certain conditions (e.g. from 0, 1 M to 10𝜇M), while among other things they change (e.g. from 0.1 M to 1 mM) as the ionic strength in the aqueous bulk solution varies. Our atomistic simulations suggest a prominent role of contact ion pairs in the Stern layer that interact specifically with the oxide surface, responsible for their decoupled kinetics from the EDL layers in bulk salinity transitions.

Introduction

Thanks to heterodyne-detected SHG (HD-SHG) providing point estimates for both 𝜒(2) and the 𝜒(3)Φ(0)𝑡 𝑜𝑡 product, one can now start thinking about separation processes in the Stern and diffuse layers . Experiments apparently show that the dynamics in the Stern and Diffuse layers are decoupled under certain conditions (eg large salinity change), while they are strongly coupled under other conditions (eg small salinity change) that can be easily identified.

Simulation Method and Calculation of SHG Responses

Both derivatives of the linear polarizabilities and the dipole moment are obtained from Backus et al. The tile angle (𝜃0) is the angle of the OH bond with respect to the surface normal vector that is antiparallel to the associated Si–O bond.

Table 9.1: Lennard-Jones parameters and atomic charge of water, ions, and model silica atoms.

Results and Discussion

In the case of the solvent-separated and non-ion pairs, semipermeable boundaries (see Section 9.3) are included to prevent Na+ ions from reaching the interface. First and third moments of the water orientation angle and the oxygen density of the water as a function of the distance to the interface (right) for the different models and scenarios investigated.

Figure 9.3: Heterodyne-detected SHG measurements on abrupt salinity transitions.

Conclusion

These results are likely to be influenced by how strongly the ions are bound in the inner Helmholtz plane, indicating that they should be subject to ion-specific effects, such as those characterized by the Hofmeister series [64]. Atomistic simulations indicate a prominent role of CIPs, as opposed to SSIPs in the Stern layer, in determining whether the SHG reactions in EDL layers are coupled or uncoupled.

Appendix

Water exchange at a hydrated platinum electrode is rare and concerted." In: The Journal of Physical Chemistry C pp. Computer simulations of NaCl association in polarizable water.” In: The Journal of Chemical Physics pp.