Boron-Doping Induced Electron Delocalization in Fluorophosphate Cathode: Enhanced Na-Ion Diffusivity and Sodium-Ion Full Cell Performance.

Na3 V2 (PO4 )2 O2 F (NVPOF) is widely accepted as advanced cathode material for sodium-ion batteries with high application prospects ascribing to its considerable specific capacity and high working voltage. However, challenges in the full realization of its theoretical potential lie in the novel structural design to accelerate its Na+ diffusivity. Herein, considering the important role of polyanion groups in constituting Na+ diffusion tunnels, boron (B) is doped at the P-site to obtain Na3 V2 (P2- x Bx O8 )O2 F (NVP2- x Bx OF). As evidenced by density functional theory modeling, B-doping induces a dramatic decrease in the bandgap. Delocalization of electrons on the O anions in BO4 tetrahedra is observed in NVP2- x Bx OF, which dramatically lowers the electrostatic resistance experienced by Na+ . As a result, the Na+ diffusivity in the NVP2- x Bx OF cathode has accelerated up to 11 times higher, which secures a high rate property (67.2 mAh g-1 at 60 C) and long cycle stability (95.9% capacity retention at 108.6 mAh g-1 at 10 C after 1000 cycles). The assembled NVP1.90 B0.10 OF//Se-C full cell demonstrates exceptional power/energy density (213.3 W kg-1 @ 426.4 Wh kg-1 and 17970 W kg-1 @ 119.8 Wh kg-1 ) and outstanding capability to withstand long cycles (90.1% capacity retention after 1000 cycles at 105.3 mAh g-1 at 10 C).

Effect of Si on the Oxidation Behaviors of Ti3 Al1-x Six C2 at 1000 °C.

In this work, Ti3 Al1-x Six C2 (x=0, 0.2, 0.4, and 0.6) with Al/Si solid solution structure are synthesized, and the effects of Si on their oxidation behaviors at 1000 °C are evaluated. The addition of Si not only contributes to the formation of Ti5 Si3 impurity but also affects the composition of the oxide scale. Particularly, the incorporation of Si in the TiO2 lattice is demonstrated, which alters the formation energy of the (110) plane in TiO2 , thus leading to the preferential growth of Si-doped TiO2 to dendritic congeries. Moreover, the Si addition is believed to affect mass transportation during the oxidation process, which accelerates the formation of a continuous Al2 O3 layer in the oxide scale. With an optimized Si content, the oxidation of Ti3 Al1-x Six C2 is restrained. However, with excess Si content, the continuity of the resulting Al2 O3 layer is destroyed, thus the oxidation rate rises again.

From Solid-Solution MXene to Cr-Substituted Na3V2(PO4)3: Breaking the Symmetry of Sodium Ions for High-Voltage and Ultrahigh-Rate Cathode Performance.

Stabilizing Na+ accessibility at high voltage and accelerating Na+ diffusivity are pressing issues to further enhance the energy density of the Na3V2(PO4)3 (NVP) cathode for sodium-ion batteries (SIBs). Herein, by taking a V/Cr solid-solution MXene as a precursor, a facile in-situ reactive transformation strategy to embed Cr-substituted NVP (NVCP) nanocrystals in a dual-carbon network is proposed. Particularly, the substituted Cr atom triggers the accessibility of additional Na+ in NVCP, which is demonstrated by an additional reversible redox plateau at 4.0 V even under extreme conditions. More importantly, the Cr atom alters the Na+ ordering at the Na2 sites with an additional intermediate phase formation during charging/discharging, thus reducing the energy barriers for Na+ migration. As a result, Na+ diffusivity in NVCP accelerates to 2-3 orders of magnitude higher than that of NVP. Eventually, the NVCP cathode exhibits extraordinarily high-rate capability (78 mA g-1 at 200 C and 68975 W kg-1), outstanding cycle stability (over 1500 cycles at 10 C), excellent low-temperature property, and full cell performance.

A Review of MnO2 Composites Incorporated with Conductive Materials for Energy Storage.

Manganese dioxide (MnO2 ) has been widely used in the field of energy storage due to its high specific capacitance, low cost, natural abundance, and being environmentally friendly. However, suffering from poor electrical conductivity and high dissolvability, the performance of MnO2 can no longer meet the needs of rapidly growing technological development, especially for the application as electrode material in metal-ion batteries and supercapacitors. In this review, recent studies on the development of binary or multiple MnO2 -based composites with conductive components for energy storage are summarized. Firstly, general preparing methods for MnO2 -based composites are introduced. Subsequently, the binary and multiple MnO2 -based composites with carbon, conducting polymer, and other conductive materials are discussed respectively. The improvement in their performance is summarized as well. Finally, perspectives on the practical applications of MnO2 -based composites are presented.

Developments in Surface/Interface Engineering of Ni-Rich Layered Cathode Materials.

Ni-rich layered cathodes with high energy densities reveal an enormous potential for lithium-ion batteries (LIBs), however, their poor stability and reliability have inhibited their application. To ensure their stability over extensive cycles at high voltage, surface/interface modifications are necessary to minimize the adverse reactions at the cathode-electrolyte interface (CEI), which is a critical factor impeding electrode performance. Therefore, this review provides a comprehensive discussion on the surface engineering of Ni-rich cathode materials for enhancing their lithium storage property. Based on the structural characteristics of the Ni-rich cathode, the major failure mechanisms of these structures during synthesis and operation are summarized. Then the existing surface modification techniques are discussed and compared. Recent breakthroughs in various surface coatings and modification strategies are categorized and their unique functionalities in structural protection and performance-enhancing are elaborated. Finally, the challenges and outlook on the Ni-rich cathode materials are also proposed.

Ni-Directed biphase N-doped Mo2C as an efficient hydrogen evolution catalyst in both acidic and alkaline conditions.

The development of efficient and low-cost catalysts is of great significance for the future application of the electrocatalytic hydrogen evolution reaction (HER). Herein, a series of Ni,N co-doped Mo2C nanostructures (Nix-Mo2C/N) with different Ni content levels are fabricated. The phase-directing effect of Ni on Mo2C/N is observed, which is in charge of the phase transformation of Mo2C/N from an α- to a ß-phase. At the optimized Ni-doping level, biphase Ni15-Mo2C/N exhibits outstanding HER activity under both acidic and alkaline conditions. In particular, under alkaline conditions, Ni15-Mo2C/N delivers an overpotential of only 105.0 mV, accompanied by a low Tafel slope of 44.96 mV dec-1. The performance is comparable to commercial 20% Pt/C and higher than most state-of-the-art Mo2C-based catalysts as well.

Promoting the Water-Reduction Kinetics and Alkali Tolerance of MoNi4 Nanocrystals via a Mo2 TiC2 Tx Induced Built-In Electric Field.

Mo-Ni alloy-based electrocatalysts are regarded as promising candidates for the hydrogen evolution reaction (HER), despite their vulnerable stability in alkaline solution that hampers further application. Herein, Mo2 TiC2 Tx MXene, is employed as a support for MoNi4 alloy nanocrystals (NCs) to fabricate a unique nanoflower-like MoNi4 -MXn electrocatalyst. A remarkably strong built-in electric field is established at the interface of two components, which facilitates the electron transfer from Mo2 TiC2 Tx to MoNi4 . Due to the accumulation of electrons at the MoNi4 sites, the adsorption of the catalytic intermediates and ionic species on MoNi4 is affected consequently. As a result, the MoNi4 -MX10 nanohybrid exhibits the lowest overpotential, even lower than 10% Pt/C catalyst at the current density of 10 mA cm-2 in 1 m KOH solution (122.19 vs 129.07 mV, respectively). Furthermore, a lower Tafel slope of 55.88 mV dec-1 is reported as compared to that of the 10% Pt/C (65.64 mV dec-1 ). Additionally, the MoNi4 -MX10 catalyst also displays extraordinary chemical stability in alkaline solution, with an activity loss of only 0.15% per hour over 300 h of operation. This reflects the great potential of using MXene-based interfacial engineering for the synthesis of a highly efficient and stable electrocatalyst.

Catalytic polysulfides immobilization within a S/C-Co-N hollow cathode obtained by nonthermal imprison route.

Lithium-sulfur (Li-S) batteries have hitherto attracted dramatic research interests as an optional high-energy output candidate to replace the traditional lithium-ion batteries on account of its high energy density and low cost. Nonetheless, their kinetics arrearage and detrimental "shuttling effect" caused by the migration of soluble lithium polysulfide (LiPS) intermediates severely limit its practical application. Here, by a nonthermal route sulfur is in-situ imprisoned into Co/N-codoped hollow carbon sphere (NC-Co) to construct an integrated S/C-Co-N hollow cathode (S@NC-Co) and directly applied in Li-S batteries, which effectively avoids complex template removal and sulfur infiltration process. The hollow NC-Co sphere not only restricts polysulfides migration via physical confinement but also enhances polysulfides conversion through redox-active electro-catalysis. Moreover, the hollow structure has large cavity offering sufficient space to accommodate volume expansion and excellent conductivity promising efficient electron/charge transfer. As a result, the batteries assembled by the S@NC-Co cathode achieve low polarization and high-rate capability (551 mAh g-1 at 4C). Remarkably, the batteries also present an outstanding long-term durability over 800 cycles at 1C, in which the capacity attenuation is merely 0.06 % per cycle. This work demonstrates a novel strategy in designing hierarchical structures or nanoreactors for electrochemical reactions and energy storage systems.

Overexpression of the Aldehyde Dehydrogenase Gene ZmALDH Confers Aluminum Tolerance in Arabidopsis thaliana.

Aluminum (Al) toxicity is the main factor limiting plant growth and the yield of cereal crops in acidic soils. Al-induced oxidative stress could lead to the excessive accumulation of reactive oxygen species (ROS) and aldehydes in plants. Aldehyde dehydrogenase (ALDH) genes, which play an important role in detoxification of aldehydes when exposed to abiotic stress, have been identified in most species. However, little is known about the function of this gene family in the response to Al stress. Here, we identified an ALDH gene in maize, ZmALDH, involved in protection against Al-induced oxidative stress. Al stress up-regulated ZmALDH expression in both the roots and leaves. The expression of ZmALDH only responded to Al toxicity but not to other stresses including low pH and other metals. The heterologous overexpression of ZmALDH in Arabidopsis increased Al tolerance by promoting the ascorbate-glutathione cycle, increasing the transcript levels of antioxidant enzyme genes as well as the activities of their products, reducing MDA, and increasing free proline synthesis. The overexpression of ZmALDH also reduced Al accumulation in roots. Taken together, these findings suggest that ZmALDH participates in Al-induced oxidative stress and Al accumulation in roots, conferring Al tolerance in transgenic Arabidopsis.

Multifunctional ionic liquid-assisted interfacial engineering towards ZnS nanodots with ultrastable high-rate lithium storage performance.

In this article, a new zinc-containing ionic liquid (IL) [HMMIm]2[ZnCl4] (HMMIm = 1-hexyl-2,3-dimethyl-imidazolium) is designed, which acts as a multifunctional source for the interfacial engineering of ZnS nanodots (NDs). Given the electrostatic interaction driven by the imidazolium cation, the steric effect of the alkyl chain, and the in situ released Zn ion from the IL, [HMMIm]2[ZnCl4] shows great advantages in controlling the formation of ZnS NDs. Based on this strategy, a nanocomposite consisting of homodispersed ZnS NDs anchored on sulfur/nitrogen dual-doped reduced graphene oxide (ZnS-NDs@SNG) is prepared. When evaluated as an anode material for lithium-ion batteries (LIBs), the nanocomposite delivers high reversible specific capacity, excellent high-rate performance, and superior cycling life. In particular, a discharge capacity of 648.1 mA h g-1 can be achieved at a high current density (10.0 A g-1) over 5000 cycles. Benefitting from the multifunctional IL and the simple synthesis protocol, the IL-assisted interfacial engineering strategy will enable a new avenue for the controllable synthesis of metal-sulfide-based anode materials.

Recent Advanced on the MXene-Organic Hybrids: Design, Synthesis, and Their Applications.

With increasing research interest in the field of flexible electronics and wearable devices, intensive efforts have been paid to the development of novel inorganic-organic hybrid materials. As a newly developed two-dimensional (2D) material family, MXenes present many advantages compared with other 2D analogs, especially the variable surface terminal groups, thus the infinite possibility for the regulation of surface physicochemical properties. However, there is still less attention paid to the interfacial compatibility of the MXene-organic hybrids. To this end, this review will briefly summarize the recent progress on MXene-organic hybrids, offers a deeper understanding of the interaction and collaborative mechanism between the MXenes and organic component. After the discussion of the structure and surface characters of MXenes, strategies towards MXene-organic hybrids are introduced based on the interfacial interactions. Based on different application scenarios, the advantages of MXene-organic hybrids in constructing flexible devices are then discussed. The challenges and outlook on MXene-organic hybrids are also presented.

MXenes as a versatile platform for reactive surface modification and superior sodium-ion storages.

Owing to the large surface area and adjustable surface properties, the two-dimensional (2D) MXenes have revealed the great potential in constructing hybrid materials and for Na-ion storage (SIS). In particular, the facilitated Na-ion adsorption, intercalation, and migration on MXenes can be achieved by surface modification. Herein, a new surface modification strategy on MXenes, namely, the reactive surface modification (RSM), is focused and illustrated, while the recent advances in the research of SIS performance based on MXenes and their derivatives obtained from the RSM process are briefly summarized as well. In the second section, the intrinsic surface chemistries of MXenes and their surface-related physicochemical properties are first summarized. Meanwhile, the close relationship between the surface characters and the Na-ion adsorption, intercalation, and migration on MXenes is emphasized. Following the SIS properties of MXenes, the surface-induced SIS property variations, and the SIS performance of RSM MXene-based hybrids are discussed progressively. Finally, the existing challenges and prospects on the RSM MXene-based hybrids for SIS are proposed.

Synergy of Nb Doping and Surface Alloy Enhanced on Water-Alkali Electrocatalytic Hydrogen Generation Performance in Ti-Based MXene.

Presented are the theoretical calculation and experimental studies of a Ti3C2T x MXene-based nanohybrid with simultaneous Nb doping and surface transition metal alloy modification. Guided by the density functional theory calculation, the Nb doping can move up the Fermi energy level to the conduction band, thus enhancing the electronic conductivity. Meanwhile, the surface modification by Ni/Co alloy can moderate the surface M-H affinity, which will further enhance the hydrogen evolution reaction (HER) activity. A series of Ni/Co alloy attached on Nb-doped Ti3C2T x MXene nanohybrids (denoted as NiCo@NTM) are successfully prepared. As expected, the Ni0.9Co0.1@ NTM nanohybrids present an extraordinary HER activity in alkaline solution, which only needs an overpotential (η) of 43.4 mV to reach the current density of 10 mA cm-2 in 1 m KOH solution and shows good stability. The performance of the Ni0.9Co0.1@ NTM nanohybrids is comparable to the commercial 10% Pt/C electrode (34.4 mV@10 mA cm-2) and is better than most state-of-the-art Pt-free HER catalysts. Inspired by the facile synthesis process and chemical versatility of both MXene and transition metal alloys, the nanohybrids reported here are promising non-noble metal electrocatalysts for water-alkali electrolysis.

Surface Modified MXene-Based Nanocomposites for Electrochemical Energy Conversion and Storage.

In recent years, the rapidly growing attention on MXenes makes the material a rising star in the 2D materials family. Although most researchers' interests are still focused on the properties of bare MXenes, little attention has been paid to the surface chemistry of MXenes and MXene-based nanocomposites. To this end, this Review offers a comprehensive discussion on surface modified MXene-based nanocomposites for energy conversion and storage (ECS) applications. Based on the structure and reaction mechanism, the related synthesis methods toward MXenes are briefly summarized. After the discussion of existing surface modification techniques, the surface modified MXene-based nanocomposites and their inherent chemical principles are presented. Finally, the application of these surface modified nanocomposites for supercapacitors (SCs), lithium/sodium-ion batteries (LIBs/SIBs), and electrocatalytic water splitting is discussed. The challenges and prospects of MXene-based nanocomposites for future ECS applications are also presented.

Layered Trichalcogenidophosphate: A New Catalyst Family for Water Splitting.

Due to the rapidly increasing demand for energy and environmental sustainability, stable and economical hydrogen production has received increasing attention in the past decades. In this regard, hydrogen production through photo- or electrocatalytic water splitting has continued to gain ever-growing interest. However, the existing catalysts are still unable to fulfill the demands of high-efficiency, low-cost, and sustainable hydrogen production. Layered metal trichalcogenidophosphate (MPQ3) is a newly developed two-dimensional material with tunable composition and electronic structure. Recently, MPQ3 has been considered a promising candidate for clean energy generation and related water splitting applications. In this minireview, we firstly introduce the structure and methods for the synthesis of MPQ3 materials. In the following sections, recent developments of MPQ3 materials for photo- and electrocatalytic water splitting are briefly summarized. The roles of MPQ3 materials in different reaction systems are also discussed. Finally, the challenges related to and prospects of MPQ3 materials are presented on the basis of the current developments.

Porous MXene Frameworks Support Pyrite Nanodots toward High-Rate Pseudocapacitive Li/Na-Ion Storage.

Presented are the novel Ti3C2 T x MXene-based nanohybrid that decorated by pyrite nanodots on its surface (denoted as FeS2@MXene). The nanohybrid was obtained by the one-step sulfurization of self-assembled iron hydroxide@MXene precursor. When used for Li/Na-ion storage, the FeS2@MXene nanohybrid present excellent rate capabilities. Particularly, for Li-ion storage, an elevated reversible specific capacity of 762 mAh g-1 at 10 A g-1 after 1000 cycles was achieved. And for Na-ion storage, the FeS2@MXene nanohybrid also delivering a reversible specific capacity of 563 mAh g-1 after 100 cycles at a current density of 0.1 A g-1.

[CH3NH3]2Ag4SnIV2SnIIS8: An Open-Framework Mixed-Valent Chalcogenidostannate.

An open-framework chalcogenidostannate, namely, [CH3NH3]2Ag4SnIV2SnIIS8 (1), has been solvothermally synthesized and structurally characterized, which represents the first organically templated three-dimensional (3D) Ag-Sn-S compound containing the mixed valence of Sn(IV)/Sn(II) and displays visible-light-driven photocatalytic activity for degradation of crystal violet (CV).

Two novel selenidostannates from mixed structure-directing systems: the large ten-membered ring of [Sn3Se4] semicubes and the 3D [Sn4Se9]n(2n-) with multi-channels.

Ionothermal syntheses, characterization and properties of two selenidostannate compounds with two- or three-dimensional (D) skeletons by utilizing the synergistic structure-directing effects of the ionic liquid (IL) [Bmmim]Cl (Bmmim = 1-butyl-2,3-dimethylimidazolium) and in-situ generated metal-amine complexes (MACs), namely, 2D-(Bmmim)2[Ni(teta)(en)][Sn3Se7]2 (1, teta = triethylenetetramine, en = ethylenediamine) and 3D-(Bmmim)1.5(dienH)0.5Ni(dien)2[Sn4Se9]2 (2, dien = diethylenetriamine) are presented. Single-crystal X-ray diffraction analyses revealed that compound 1 possesses a lamellar anionic [Sn3Se7]n(2n-) structure comprising a large ten-membered ring with a window size of 24.85 × 13.38 Å when considering the [Sn3Se4] semicube as a member. While 2 features a 3D [Sn4Se9]n(2n-) framework with orthogonally intersecting channels where the three different types of cations are filled. The successful isolation of these two compounds demonstrated again that the mixed SDA strategy is promising for the synthesis of novel crystalline selenidostannates.

Synthesis, Structure, Band Gap, and Near-Infrared Photosensitivity of a New Chalcogenide Crystal, (NH4)4Ag12Sn7Se22.

A new chalcogenide crystal, (NH4)4Ag12Sn7Se22 (FJSM-STS), has been solvothermally synthesized. The crystal structure, which is composed of arrays of [Sn3Se9]n(6n-) chains interconnecting [SnAg6Se10]n(10n-) and [Ag3Se4]n(5n-) layers, is unprecedented among the reported A/Ag/Sn/Q (A = cation; Q = S, Se, and Te) compounds. Optical absorption together with theoretical calculations of the band structure indicate a direct band gap of 1.21 eV for FJSM-STS, which is close to the ideal band gap to maximize the photoconversion efficiency proposed by Shockley and Queisser. The toxic-metal-free crystal of FJSM-STS exhibits obvious photosensitivity in the near-infrared range. The variates of power and temperature on the photosensitivity have been studied.

Synthesizing 2D and 3D Selenidostannates in Ionic Liquids: The Synergistic Structure-Directing Effects of Ionic Liquids and Metal-Amine Complexes.

Presented are the ionothermal syntheses, characterizations, and properties of a series of two- and three-dimensional selenidostannate compounds synergistically directed by metal-amine complex (MAC) cations and ionic liquids (ILs) of [Bmmim]Cl (Bmmim=1-butyl-2,3-dimethylimidazolium). Four selenidostannates, namely, 2D-(Bmmim)3 [Ni(en)3 ]2 [Sn9 Se21 ]Cl (1, en=ethylenediamine), 2D-(Bmmim)8 [Ni2 (teta)2 (µ-teta)]Sn18 Se42 (2, teta=triethylenetetramine), 2D-(Bmmim)4 [Ni(tepa)Cl]2 [Ni(tepa)Sn12 Se28 ] (3, tepa=tetraethylenepentamine), and 3D-(Bmmim)2 [Ni(1,2-pda)3 ]Sn8 Se18 (4, 1,2-pda=1,2-diaminopropane), were obtained. Single-crystal X-ray diffraction analyses revealed that compounds 1 and 2 possess a lamellar anionic [Sn3 Se7 ]n (2n-) structure comprising distinct eight-membered ring units, whereas 3 features a MAC-decorated anionic [Ni(tepa)Sn12 Se28 ]n (6n-) layered structure. In contrast to 1-3, compound 4 exhibits a 3D open framework of anionic [Sn4 Se9 ]n (2n-) . The structural variation from 1 to 4 clearly indicates that on the basis of the synergistic structure-directing ability of the MACs and ILs, variation of the organic polyamine ligand has a significant impact on the formation of selenidostannates.