There is an urgent global need for electrochemical energy storage that includes materials that can provide simultaneous high power and high energy density. One strategy to achieve this goal is with ...pseudocapacitive materials that take advantage of reversible surface or near-surface Faradaic reactions to store charge. This allows them to surpass the capacity limitations of electrical double-layer capacitors and the mass transfer limitations of batteries. The past decade has seen tremendous growth in the understanding of pseudocapacitance as well as materials that exhibit this phenomenon. The purpose of this Review is to examine the fundamental development of the concept of pseudocapacitance and how it came to prominence in electrochemical energy storage as well as to describe new classes of materials whose electrochemical energy storage behavior can be described as pseudocapacitive.
The 1T phase of transition-metal dichalcogenides (TMDs) has been demonstrated in recent experiments to display excellent catalytic activity for hydrogen evolution reaction (HER), but the catalytic ...mechanism has not been elucidated so far. Herein, using 1T MoS2 as the prototypical TMD material, we studied the HER activity on its basal plane from periodic density functional theory (DFT) calculations. Compared to the nonreactive basal plane of 2H phase MoS2, the catalytic activity of the basal plane of 1T phase MoS2 mainly arises from its affinity for binding H at the surface S sites. Using the binding free energy (ΔG H) of H as the descriptor, we found that the optimum evolution of H2 will proceed at surface H coverage of 12.5% ∼ 25%. Within this coverage, we examined the reaction energy and barrier for the three elementary steps of the HER process. The Volmer step was found to be facile, whereas the subsequent Heyrovsky reaction is kinetically more favorable than the Tafel reaction. Our results suggest that at low overpotential, HER can take place readily on the basal plane of 1T MoS2 via the Volmer–Heyrovsky mechanism. We further screened the dopants for the HER activity and found that substitutional doping of the Mo atom by metals such as Mn, Cr, Cu, Ni, and Fe can make 1T MoS2 a better HER catalyst.
The continuous development of total synthesis chemistry has allowed many organic and biomolecules to be produced with known synthetic history-that is, a complete set of step reactions in their ...synthetic routes. Here, we extend such molecular-level precise reaction routes to nanochemistry, particularly to a seed-mediated synthesis of inorganic nanoparticles. By systematically investigating the time-dependent abundance of 35 intermediate species in total, we map out relevant step reactions in a model size growth reaction from molecularly pure Au
to Au
nanoparticles. The size growth of Au nanoparticles involves two different size-evolution processes (monotonic LaMer growth and volcano-shaped aggregative growth), which are driven by a sequential 2-electron boosting of the valence electron count of Au nanoparticles. Such fundamental findings not only provide guiding principles to produce other sizes of Au nanoparticles (e.g., Au
), but also represent molecular-level insights on long-standing puzzles in nanochemistry, including LaMer growth, aggregative growth, and digestive ripening.Synthetic nanochemistry currently lacks the molecular step-by-step routes afforded to organic chemistry by total synthesis. Here, the authors track the seeded growth of atom-precise gold nanoclusters using mass spectrometry, revealing that the clusters evolve through a series of intermediates in two-electron steps.
Porous liquids are a type of porous materials that engineer permanent porosity into unique flowing liquids, exhibiting promising functionalities for a variety of applications. Here a Type I porous ...liquid is synthesized by transforming porous organic cages into porous ionic liquids via a supramolecular complexation strategy. Simple physical mixing of 18‐crown‐6 with task‐specific anionic porous organic cages affords a porous ionic liquid with anionic porous organic cages as the anionic parts and 18‐crown‐6/potassium ion complexes as the cationic parts. In contrast, mixing of 15‐crown‐5 and anionic porous organic cages in a 2:1 ratio gives only solids, while the addition of excess 15‐crown‐5 affords a Type II porous liquid. The permanent porosity in the cage‐based porous liquids has been also confirmed by molecular simulation, positron (e+) annihilation lifetime spectroscopy, and enhanced gas sorption capacity compared with pure crown ethers.
A Type I porous liquid is synthesized by transforming porous organic cages into porous ionic liquids via a supramolecular complexation strategy. Simple physical mixing of 18‐crown‐6 with an anionic porous organic cage affords a porous ionic liquid with anionic porous organic cages as the anionic parts and 18‐crown‐6/potassium ion complexes as the cationic parts.
Although the coordinates of the metal atoms can be accurately determined by X‐ray crystallography, locations of hydrides in metal nanoclusters are challenging to determine. In principle, neutron ...crystallography can be employed to pinpoint the hydride positions, but it requires a large crystal and a neutron source, which prevents its routine use. Here, we present a deep‐learning approach that can accelerate determination of hydride locations in single‐crystal X‐ray structure of metal nanoclusters of different sizes. We demonstrate the efficiency of our method in predicting the most probable hydride sites and their combinations to determine the total structure for two recently reported copper nanoclusters, Cu25H10(SPhCl2)183− and Cu61(StBu)26S6Cl6H14+ whose hydride locations have not been determined by neutron diffraction. Our method can be generalized and applied to other metal systems, thereby eliminating a bottleneck in atomically precise metal hydride nanochemistry.
Deep convolutional neural networks, trained on existing examples with known hydride locations from neutron diffraction, were able to accurately predict hydride locations given an X‐ray structure of copper‐hydride nanoclusters, thereby relieving the need of neutron diffraction.
Nanostructured birnessite exhibits high specific capacitance and nearly ideal capacitive behaviour in aqueous electrolytes, rendering it an important electrode material for low-cost, high-power ...energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both Faradaic (involving redox) and non-Faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite's response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy and operando atomic force microscope dilatometry to provide a holistic understanding of its structural, gravimetric and mechanical responses. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite, ReaxFF reactive force field-based molecular dynamics and ReaxFF-based grand canonical Monte Carlo simulations on the dynamics at the birnessite-water-electrolyte interface. We show that capacitive charge storage in birnessite is governed by interlayer cation intercalation. We conclude that the intercalation appears capacitive due to the presence of nanoconfined interlayer structural water, which mediates the interaction between the intercalated cation and the birnessite host and leads to minimal structural changes.
The LiTaCl6 solid electrolyte has the lowest activation energy of ionic conduction at ambient conditions (0.165 eV), with a record high ionic conductivity for a ternary compound (11 mS cm−1). ...However, the mechanism has been unclear. We train machine‐learning force fields (MLFF) on ab initio molecular dynamics (AIMD) data on‐the‐fly and perform MLFF MD simulations of AIMD quality up to the nanosecond scale at the experimental temperatures, which allows us to predict accurate activation energy for Li‐ion diffusion (at 0.164 eV). Detailed analyses of trajectories and vibrational density of states show that the large‐amplitude vibrations of Cl− ions in TaCl6− enable the fast Li‐ion transport by allowing dynamic breaking and reforming of Li−Cl bonds across the space in between the TaCl6− octahedra. We term this process the dynamic‐monkey‐bar mechanism of superionic Li+ transport which could aid the development of new solid electrolytes for all‐solid‐state lithium batteries.
Machine‐learning force field molecular dynamics simulations reveal the superionic Li+ transport in glassy LiTaCl6 via the dynamic monkey bar mechanism–the high density and dynamics of the vibrating Cl− ions (the dynamic bars) allow Li ions to hold on to them while moving fast through the lattice.
Precise control of alloying sites has long been a challenging pursuit, yet little has been achieved for the atomic-level manipulation of metallic nanomaterials. Here we describe utilization of a ...surface motif exchange (SME) reaction to selectively replace the surface motifs of parent Ag
(SR)
(SR = thiolate) nanoparticles (NPs), leading to bimetallic NPs with well-defined molecular formula and atomically-controlled alloying sites in protecting shell. A systematic mass (and tandem mass) spectrometry analysis suggests that the SME reaction is an atomically precise displacement of SR-Ag(I)-SR-protecting modules of Ag NPs by the incoming SR-Au(I)-SR modules, giving rise to a core-shell Ag
@Au
(SR)
. Theoretical calculation suggests that the thermodynamically less favorable core-shell Ag@Au nanostructure is kinetically stabilized by the intermediate Ag
shell, preventing inward diffusion of the surface Au atoms. The delicate SME reaction opens a door to precisely control the alloying sites in the protecting shell of bimetallic NPs with broad utility.
CO2 capture: Protic ionic liquids (PILs) from a superbase and fluorinated alcohol, imidazole, pyrrolinone, or phenol were designed to capture CO2 based on the reactivity of their anions to CO2. These ...PILs are capable of rapid and reversible capture of about one equivalent of CO2, which is superior to those sorption systems based on traditional aprotic ILs.
What a catch! Basic ionic liquids (ILs) based on a phosphonium hydroxide derivative can be tuned for CO2 capture by varying the weak proton donors, which have different pKa values. The stability, ...absorption capacity, and absorption enthalpy of the ILs could be easily tuned: the best IL for CO2 capture has good stability (>300 °C), energy saving (ca. 56 kJ mol−1), and equimolar absorption capability.
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