Surface-Enriched Room-Temperature Liquid Bismuth for Catalytic CO2 Reduction.

Bismuth-based electrocatalysts are effective for carbon dioxide (CO2) reduction to formate. However, at room temperature, these materials are only available in solid state, which inevitably suffers from surface deactivation, declining current densities, and Faradaic efficiencies. Here, the formation of a liquid bismuth catalyst on the liquid gallium surface at ambient conditions is shown as its exceptional performance in the electrochemical reduction of CO2 (i.e., CO2RR). By doping a trace amount of bismuth (740 ppm atomic) in gallium liquid metal, a surface enrichment of bismuth by over 400 times (30 at%) in liquid state is obtained without atomic aggregation, achieving 98% Faradic efficiency for CO2 conversion to formate over 80 h. Ab initio molecular simulations and density functional theory calculations reveal that bismuth atoms in the liquid state are the most energetically favorable sites for the CO2RR intermediates, superior to solid Bi-sites, as well as joint GaBi-sites. This study opens an avenue for fabricating high-performing liquid-state metallic catalysts that cannot be reached by elementary metals under electrocatalytic conditions.

The Dual Functions of Defect-Rich Carbon Nanotubes as Both Conductive Matrix and Efficient Mediator for LiS Batteries.

LiS batteries are considered a promising energy storage system owing to the great abundance of sulfur and its high specific capacity. Polysulfide shuttling and sluggish reaction kinetics in sulfur cathodes significantly degrade the cycle life of LiS batteries. A modified method is employed to create defects in carbon nanotubes (CNTs), anchoring polysulfides, and accelerating electrochemical reactions. The defect-rich CNTs (D-CNT) enable dramatic improvement in both cycling and rate performance. A specific capacity of 600 mAh g-1 with a current density of 0.5 C is achieved after 400 cycles, and even at a very high current density (5.0 C), a specific capacity of 434 mAh g-1 is observed. Cycling stability up to 1000 cycles is also achieved under the conditions of high sulfur loading and lean electrolyte. Theoretical calculations revealed that the improvement is mainly attributable to the electronic structure of defect-rich carbon, which has higher binding energy with polysulfides because of the upshift of the p-band center. Furthermore, rotating disk electrode measurements demonstrate that the defect-rich carbon can accelerate the polysulfide conversion process. It is anticipated that this new design strategy can be the starting point for mediator-like carbon materials with good conductivity and high catalytic activity for LiS batteries.

Understanding the Effects of the Low-Concentration Electrolyte on the Performance of High-Energy-Density Li-S Batteries.

High-energy-density Li-S batteries have been impeded by low power rate and low sulfur utilization of high-sulfur-loading cathode and unstable Li metal anode. Herein, a new method protocol was proposed to separately investigate the effects of low-concentration electrolytes on the cathode and the anode for Li-S batteries. It was found that 0.5 M LiTFSI showed better cycling stability than the standard concentration of 1.0 M LiTFSI under the condition of high sulfur loading due to its better wettability toward the electrode. In addition, the low-concentration electrolyte could improve the stability of the Li-electrolyte interface, which was attributable to a higher content of the organic component in the solid electrolyte interface (SEI), owing to the participation of more solvent in the buildup of the SEI. The flexible and elastic organic components could be more capable of accommodating the volume changes in the Li metal anode. Consequently, the low-concentration electrolyte could be more suitable for high-energy-density Li-S batteries. We anticipate this research could provide some inspirations for the development of high-energy-density and low-cost Li-S batteries.

Lithium Metal Electrode with Increased Air Stability and Robust Solid Electrolyte Interphase Realized by Silane Coupling Agent Modification.

The quality of the solid electrolyte interphase (SEI) layer is the decisive factor for the electrochemical performance of Li-metal-based batteries. Due to the absence of effective bonding, a natural SEI layer may exfoliate from the Li anode during interfacial fluctuations. Here, a silane coupling agent is introduced to serve as an adhesion promoter to bridge these two dissimilar materials via both chemical bonding and physical intertwining effects. Its inorganic reactive groups can combine with the Li substrate by forming LiOSi bonds, while organic functional groups can take part in the formation of the SEI layer and thereby bond with SEI components. Li metal electrodes with silane coupling agent modification exhibit excellent electrochemical performance, even under extreme testing conditions. This modification layer with dense structure could also protect the Li metal from corrosion by air, evidenced by the comparable electrochemical activity of the modified Li metal electrodes even after being exposed in air for 2 h. This design provides a promising pathway for the development of Li metal electrodes that will be stable both in electrolyte and in air.

Li2 S-Based Li-Ion Sulfur Batteries: Progress and Prospects.

The great demand for high-energy-density batteries has driven intensive research on the Li-S battery due to its high theoretical energy density. Consequently, considerable progress in Li-S batteries is achieved, although the lithium anode material is still challenging in terms of lithium dendrites and its unstable interface with electrolyte, impeding the practical application of the Li-S battery. Li2 S-based Li-ion sulfur batteries (LISBs), which employ lithium-metal-free anodes, are a convenient and effective way to avoid the use of lithium metal for the realization of practical Li-S batteries. Over the past decade, studies on LISBs are carried out to optimize their performance. Herein, the research progress and challenges of LISBs are reviewed. Several important aspects of LISBs, including their working principle, the physicochemical properties of Li2 S, Li2 S cathode material composites, LISBs full batteries, and electrolyte for Li2 S cathode, are extensively discussed. In particular, the activation barrier in the initial charge process is fundamentally analyzed and the mechanism is discussed in detail, based on previous reports. Finally, perspectives on the future direction of the research of LISBs are proposed.

Dehydration-Triggered Ionic Channel Engineering in Potassium Niobate for Li/K-Ion Storage.

Boosting charge transfer in materials is critical for applications involving charge carriers. Engineering ionic channels in electrode materials can create a skeleton to manipulate their ion and electron behaviors with favorable parameters to promote their capacity and stability. Here, tailoring of the atomic structure in layered potassium niobate (K4 Nb6 O17 ) nanosheets and facilitating their application in lithium and potassium storage by dehydration-triggered lattice rearrangement is reported. The spectroscopy results reveal that the interatomic distances of the NbO coordination in the engineered K4 Nb6 O17 are slightly elongated with increased degrees of disorder. Specifically, the engineered K4 Nb6 O17 shows enhanced electrical and ionic conductivity, which can be attributed to the enlarged interlamellar spacing and subtle distortions in the fine atomic arrangements. Moreover, subsequent experimental results and calculations demonstrate that the energy barrier for Li+ /K+ diffusion is significantly lower than that in pristine K4 Nb6 O17 . Interestingly, the diffusion coefficient of K+ is one order of magnitude higher than that of Li+ , and the engineered K4 Nb6 O17 presents superior electrochemical performance for K+ to Li+ . This work offers an ionic engineering strategy to enable fast and durable charge transfer in materials, holding great promise for providing guidance for the material design of related energy storage systems.

Hierarchically scaffolded CoP/CoP2 nanoparticles: controllable synthesis and their application as a well-matched bifunctional electrocatalyst for overall water splitting.

Transition metal phosphide (TMP) nanostructures have stimulated increasing interest for use in water splitting owing to their abundant natural sources and high activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Typically, the preparation of hierarchical TMPs involves the utilization of expensive or dangerous phosphorus sources, and, in particular, the understanding of topotactic transformations of the precursors to crystalline phases-which could be utilized to enhance electrocatalytic performance-remains very limited. We, herein, report a controllable preparation of CoP/CoP2 nanoparticles well dispersed in flower-like Al2O3 scaffolds (f-CoP/CoP2/Al2O3) as a bifunctional electrocatalyst for the HER and OER via the phosphorization of a flower-like CoAl layered double hydroxide precursor. Characterization by in situ X-ray diffraction (XRD) monitored the topotactic transformation underlying the controllable formation of CoP/CoP2via tuning the phosphorization time. Electrocatalytic tests showed that an f-CoP/CoP2/Al2O3 electrode exhibited a lower onset potential and higher electrocatalytic activity for the HER and OER in the same alkaline electrolyte than electrodes of flower-like and powdered CoP/Al2O3. The enhanced electrochemical performance was experimentally supported by measuring the electrochemically active surface area. The f-CoP/CoP2/Al2O3 composite further generated a current density of 10 mA cm-2 at 1.65 V when used as a bifunctional catalyst for overall water splitting. Our results demonstrate that the preparation route based on the LDH precursor may provide an alternative for investigating diverse TMPs as bifunctional electrocatalysts for water splitting.

Photodeposited Pd Nanoparticles with Disordered Structure for Phenylacetylene Semihydrogenation.

Developing effective heterogeneous metal catalysts with high selectivity and satisfactory activity for chemoselective hydrogenation of alkyne to alkene is of great importance in the chemical industry. Herein, we report our efforts to fabricate TiO2-supported Pd catalysts by a photodeposition method at room temperature for phenylacetylene semihydrogenation to styrene. The resulting Pd/TiO2 catalyst, possessing smaller Pd ensembles with ambiguous lattice fringes and more low coordination Pd sites, exhibits higher styrene selectivity compared to two contrastive Pd/TiO2 samples with larger ensembles and well-organized crystal structure fabricated by deposition-precipitation or photodeposition with subsequent thermal treatment at 300 °C. The sample derived from photodeposition exhibits greatly slow styrene hydrogenation in kinetic evaluation because the disordered structure of Pd particles in photodeposited Pd/TiO2 may prevent the formation of ß-hydride phases and probably produce more surface H atoms, which may favor high styrene selectivity.