Abstract
Populist political movements claim to be democratic in expressing what the people want, against the political establishment. These claims are misconceived to begin with in presupposing a ...definitive unitary people. Nonetheless, constitutional democracies face a special challenge to resist these claims in principle because they are unmistakably democratic sounding claims; they purport to empower popular will so that the people can rule themselves. Populist movements can be successful at the ballot box and push political culture in antidemocratic directions through democratic means, all the while claiming democratic legitimacy. The very processes of democracy are under threat. Traditionally, political winners are not motivated to change the system that saw them elected; populists are different in this regard. The populist challenge prompts a revisit of the debate about the democratic legitimacy of judges being empowered to displace the decisions of elected legislative assemblies (the constitutional review debate). An underdeveloped aspect of the constitutional review debate was the scope for courts to intervene specifically in political processes to correct them when they have gone awry and to help prevent them going awry in the first place. Judicial intervention is costly in democratic terms, and yet democracy has to be protected. This Article analyzes the search for a balance between popular will shaping democratic processes and judicially managed constitutional limitations on popular will shaping those processes. The recommended judicial role is styled as courts protecting—not perfecting—democracy, and it is a John Hart Ely-inspired modification of a separation of powers defense of constitutional review. In addressing the populist challenge, courts can, in principle, try to be a step ahead in anticipating and, where they can, slowing degradation of democracy and thereby helping to prevent it.
Zinc ion batteries using metallic zinc as the negative electrode have gained considerable interest for electrochemical energy storage, whose development is crucial for the adoption of renewable ...energy technologies, as zinc has a very high volumetric capacity (5845 mA h cm −3 ), is inexpensive and compatible with aqueous electrolytes. However, the divalent charge of zinc ions, which restricts the choice of host material due to hindered solid-state diffusion, can also pose a problem for interfacial charge transfer. Here, we report our findings on reversible intercalation of up to two Zn 2+ ions in layered V 3 O 7 ·H 2 O. This material exhibits very high capacity and power (375 mA h g −1 at a 1C rate, and 275 mA h g −1 at an 8C rate) in an aqueous electrolyte compared to a very low capacity and slow rate capabilities in a nonaqueous medium. Operando XRD studies, together with impedance analysis, reveal solid solution behavior associated with Zn 2+ -ion diffusion within a water monolayer in the interlayer gap in both systems, but very sluggish interfacial charge transfer in the nonaqueous electrolyte. This points to desolvation at the interface as a major factor in dictating the kinetics. Temperature dependent impedance studies show high activation energies associated with the nonaqueous charge transfer process, identifying the origin of poor electrochemical performance.
Using advanced molecular dynamics free energy sampling techniquesboth classical and ab initiowe analyze the solvation structures of multivalent cations in aprotic solvents. In contrast to previous ...studies of mono- and bivalent ions in organic solvents, mainly performed using hybrid cluster-continuum quantum chemistry calculations that rely on the assumption of uniqueness of ion solvation free energies, here we find that monatomic bivalent cations may have multiple well-defined minima, as previously reported only for water, or plateaus of free energy with respect to the ion–solvent coordination. These observations are generalized in the concept of the “ion solvation spectrum“ to highlight the rich phenomenology related to ion solvation as opposed to the normally expected free energy profiles with a single coordination minimum. Specifically, we show that a single chemical species may exhibit a multiplicity of distinctly different electrochemical properties. Using one- and two-dimensional projections of the free energy landscape, we analyze the stability of ion solvation structures and reveal minimum free energy pathways for ion (de-)solvation with low-dimensional approximations to associated kinetic barriers. Unexpectedly, we show that in some cases the process of opening the first ion solvation shell, by removing a solvent molecule, may actually drive the ion into a free energy basin with a higher coordination number. Our study highlights some deficiencies of conventional methodologies for studying ion solvation as a path to determine redox potentials and provides experimentally testable predictions.
We reveal the general mechanisms of partial reduction of multivalent complex cations in conditions specific for the bulk solvent and in the vicinity of the electrified metal electrode surface and ...disclose the factors affecting the reductive stability of electrolytes for multivalent electrochemistry. Using a combination of ab initio techniques, we clarify the relation between the reductive stability of contact-ion pairs comprising a multivalent cation and a complex anion, their solvation structures, solvent dynamics, and the electrode overpotential. We found that for ion pairs with multiple configurations of the complex anion and the Mg cation whose available orbitals are partially delocalized over the molecular complex and have antibonding character, the primary factor of the reductive stability is the shape factor of the solvation sphere of the metal cation center and the degree of the convexity of a polyhedron formed by the metal cation and its coordinating atoms. We focused specifically on the details of Mg (II) bis(trifluoromethanesulfonyl)imide in diethylene glycol dimethyl ether (Mg(TFSI)2)/diglyme) and its singly charged ion pair, MgTFSI+. In particular, we found that both stable (MgTFSI)+ and (MgTFSI)0 ion pairs have the same TFSI configuration but drastically different solvation structures in the bulk solution. This implies that the MgTFSI/dyglyme reductive stability is ultimately determined by the relative time scale of the solvent dynamics and electron transfer at the Mg–anode interface. In the vicinity of the anode surface, steric factors and hindered solvent dynamics may increase the reductive stability of (MgTFSI)+ ion pairs at lower overpotential by reducing the metal cation coordination, in stark contrast to the reduction at high overpotential accompanied by TFSI decomposition. By examining other solute/solvent combinations, we conclude that the electrolytes with highly coordinated Mg cation centers are more prone to reductive instability due to the chemical decomposition of the anion or solvent molecules. The obtained findings disclose critical factors for stable electrolyte design and show the role of interfacial phenomena in reduction of multivalent ions.
Multivalent intercalation batteries have the potential to circumvent several fundamental limitations of reigning Li-ion technologies. Such batteries will potentially deliver high volumetric energy ...densities, be safer to operate, and rely on materials that are much more abundant than Li in the Earth’s crust. The design of intercalation cathodes for such batteries requires consideration of thermodynamic aspects such as structural distortions and energetics as well as kinetic aspects such as barriers to the diffusion of cations. The layered α-V2O5 system is a canonical intercalation host for Li-ions but does not perform nearly as well for multivalent cation insertion. However, the rich V–O phase diagram provides access to numerous metastable polymorphs that hold much greater promise for multivalent cation intercalation. In this article, we explore multivalent cation insertion in three metastable polymorphs, γ′, δ′, and ρ′ phases of V2O5, using density functional theory calculations. The calculations allow for evaluation of the influence of distinctive structural motifs in mediating multivalent cation insertion. In particular, we contrast the influence of single versus condensed double layers, planar versus puckered single layers, and the specific stacking sequence of the double layers. We demonstrate that metastable phases offer some specific advantages with respect to thermodynamically stable polymorphs in terms of a higher chemical potential difference (giving rise to a larger open-circuit voltage) and in providing access to diffusion pathways that are highly dependent on the specific structural motif. The three polymorphs are found to be especially promising for Ca-ion intercalation, which is particularly significant given the exceedingly sparse number of viable cathode materials for this chemistry. The findings here demonstrate the ability to define cation diffusion pathways within layered metastable polymorphs by alteration of the stacking sequence or the thickness of the layers.
The ultrafast light-activated electrocyclic ring-opening reaction of 1,3-cyclohexadiene is a fundamental prototype of photochemical pericyclic reactions. Generally, these reactions are thought to ...proceed through an intermediate excited-state minimum (the so-called pericyclic minimum), which leads to isomerization via nonadiabatic relaxation to the ground state of the photoproduct. Here, we used femtosecond (fs) soft x-ray spectroscopy near the carbon K-edge (~284 electron volts) on a table-top apparatus to directly reveal the valence electronic structure of this transient intermediate state. The core-to-valence spectroscopic signature of the pericyclic minimum observed in the experiment was characterized, in combination with time-dependent density functional theory calculations, to reveal overlap and mixing of the frontier valence orbital energy levels. We show that this transient valence electronic structure arises within 60 ± 20 fs after ultraviolet photoexcitation and decays with a time constant of 110 ± 60 fs.
Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox ...is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li
Ni
Co
Mn
O
, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.
The molecular structure of the electrical double layer determines the chemistry in all electrochemical processes. Using x-ray absorption spectroscopy (XAS), we probed the structure of water near gold ...electrodes and its bias dependence. Electron yield XAS detected at the gold electrode revealed that the interfacial water molecules have a different structure from those in the bulk. First principles calculations revealed that ∼50% of the molecules lie flat on the surface with saturated hydrogen bonds and another substantial fraction with broken hydrogen bonds that do not contribute to the XAS spectrum because their core-excited states are delocalized by coupling with the gold substrate. At negative bias, the population of flat-lying molecules with broken hydrogen bonds increases, producing a spectrum similar to that of bulk water.
In this work, we examine the Mg-ion desolvation and intercalation process at the Chevrel phase Mo6S8 cathode surface from first principles. It is reported that in electrolytes based on chlorides in ...tetrahydrofuran (THF), Mg2+ is strongly coordinated by the counterion Cl– and can form singly charged MgCl+ and Mg2Cl3 + species in solution. During cell discharge, intercalation of Mg into the Chevrel phase requires breaking the strong, ionic Mg–Cl bond. Our simulation results indicate that the stripping of Cl– is facilitated by the existence of another cationic species, Mo on the Chevrel phase surface. Once Mg is intercalated, it leaves the counterion, Cl–, on the surface, bound to Mo. It is found that the chlorinated surface presents higher activation barriers to further intercalate Mg. Instead, the chlorinated surface continues to interact with incoming MgCl+ species and form various MgCl y surface adsorbates. With certain energy costs, the neutral MgCl2 unit may be released from these surface adsorbates to reopen Mo sites on the surface and permit continuous Mg intercalation. Presuming compatibility of chloride electrolytes with the Mg metal anode, our work implies that finding a compatible cathode material will depend critically on its ability to catalyze Mg–Cl bond breaking. This may explain the success of the Chevrel phase, with its open Mo sites, permitting intercalation of Mg from the halide solutions, whereas higher-voltage transition metal oxides, which typically lack open metal sites, require more weakly coordinating anions in their electrolytes.
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