Ultrasmall MnO Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as Efficient Anode Materials for Sodium Ion Batteries

Review and New Perspectives on Non-Layered Manganese Compounds as Electrode Material for Sodium-Ion Batteries

After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in these structural families and other oxide or halide compounds has until now not been fully explored. In this direction, the present review paper deals with the different Mn-containing solids with a non-layered structure already evaluated. The study aims to systematize the current knowledge on this topic and highlight new possibilities for further study, such as the concept of entatic state applied to electrodes.

Enhanced Electrochemical Performances of Mn3O4/Heteroatom-Doped Reduced Graphene Oxide Aerogels as an Anode for Sodium-Ion Batteries

Owing to their high theoretical capacity, transition-metal oxides have received a considerable amount of attention as potential anode materials in sodium-ion (Na-ion) batteries. Among them, Mn₃O₄ has gained interest due to the low cost of raw materials and the environmental compatibility. However, during the insertion/de-insertion process, Mn₃O₄ suffers from particle aggregation, poor conductivity, and low-rate capability, which, in turn, limits its practical application. To overcome these obstacles, we have successfully prepared Mn₃O₄ nanoparticles distributed on the nitrogen (N)-doped and nitrogen, sulphur (N,S)-doped reduced graphene oxide (rGO) aerogels, respectively. The highly crystalline Mn₃O₄ nanoparticles, with an average size of 15-20 nm, are homogeneously dispersed on both sides of the N-rGO and N,S-rGO aerogels. The results indicate that the N-rGO and N,S-rGO aerogels could provide an efficient ion transport channel for electrolyte ion stability in the Mn₃O₄ electrode. The Mn₃O₄/N- and Mn₃O₄/N,S-doped rGO aerogels exhibit outstanding electrochemical performances, with a reversible specific capacity of 374 and 281 mAh g^-1, respectively, after 100 cycles, with Coulombic efficiency of almost 99%. The interconnected structure of heteroatom-doped rGO with Mn₃O₄ nanoparticles is believed to facilitate fast ion diffusion and electron transfer by lowering the energy barrier, which favours the complete utilisation of the active material and improvement of the structure's stability.

Smoothing the Sodium-Metal Anode with a Self-Regulating Alloy Interface for High-Energy and Sustainable Sodium-Metal Batteries

Because of the large abundance of sodium (Na) as a source material and the easy fabrication of Na-containing compounds, the sodium (Na) battery is a more environmentally friendly and sustainable technology than the lithium-ion battery (LIB). Na-metal batteries (SMBs) are considered promising to realize a high energy density to overtake the cost effectiveness of LIBs, which is critically important in large-scale applications such as grid energy storage. However, the cycling stability of the Na-metal anode faces significant challenges particularly under high cycling capacities, due to the complex failure models caused by the formation of Na dendrites. Here, a universal surface strategy, based on a self-regulating alloy interface of the current collector, to inhibit the formation of Na dendrites is reported. High-capacity (10 mAh cm^-2 ) Na-metal anodes can achieve stable cycling for over 1000 h with a low overpotential of 35 mV. When paired with a high-capacity Na₃ V₂ (PO₄ )₂ F₃ cathode (7 mAh cm^-2 ), the SMB delivers an unprecedented energy density (calculated based on all the cell components) over 200 Wh kg^-1 with flooded electrolyte, or over 230 Wh kg^-1 with lean electrolyte. The dendrite-free SMB also shows high cycling stability with a capacity retention per cycle over 99.9% and an ultrahigh energy efficiency of 95.8%.

Facile Designed Manganese Oxide/Biochar for Efficient Salinity Gradient Energy Recovery in Concentration Flow Cells and Influences of Mono/Multivalent Ions

Development of effective, environmentally friendly, facile large-scale processing, and low-cost materials is critical for renewable energy production. Here, MnO_x/biochar composites were synthesized by a simple pyrolysis method and showed high performance for salinity gradient (SG) energy harvest in concentration flow cells (CFCs). The peak power density of CFCs with MnO_x/biochar electrodes was up to 5.67 W m^-2 (ave. = 0.91 W m^-2) and stabilized for 500 cycles when using 1 and 30 g L^-1 NaCl, which was attributed to their high specific capacitances and low electrode resistances. This power output was higher than all other reported MnO₂ electrodes for SG energy harvest due to the synergistic effects between MnO_x and biochar. When using a mixture with a molar fraction of 90% NaCl and 10% KCl (or Na₂SO₄, MgCl₂, MgSO₄, and CaCl₂) in both feed solutions, the peak power density decreased by 2.3-40.1% compared to 100% NaCl solution with Ca²⁺ and Mg²⁺ showing the most pronounced negative effects. Our results demonstrated that the facile designed MnO_x/biochar composite can be used for efficient SG energy recovery in CFCs with good stability, low cost, and less environmental impacts. When using natural waters as the feed solutions, pretreatment would be needed.

Nonresonant Polarized Raman Spectra Calculations of Nitrogen-Doped Single-Walled Carbon Nanotubes: Diameter, Chirality, and Doping Concentration Effects

Raman spectra of nitrogen-doped single-walled carbon nanotubes are calculated using the spectral moment’s method combined with the bond polarizability model. The influence of the nanotube diameter and chirality is investigated. We also address the important question of the effect of the N-doping concentration, and we propose an equation to estimate the doping concentration from the knowledge of the tube diameter and the frequency of the radial breathing mode.

Cobalt-Polypyrrole/Melamine-Derived Co-N@NC Catalysts for Efficient Base-Free Formic Acid Dehydrogenation and Formylation of Quinolines through Transfer Hydrogenation

It is highly desired but remains a great challenge to develop non-noble metal heterogeneous catalysts to supersede noble metal catalysts for formic acid (FA) dehydrogenation and the corresponding transfer hydrogenation reactions. Herein, we developed a simple and feasible melamine-assisted pyrolysis strategy for the preparation of atomic cobalt-nitrogen (Co-N)-anchored mesoporous carbon with high metal loading (>6.8 wt %) and high specific surface area (750 m² g^-1). Systematic investigation reveals that both the organic carbon source polypyrrole and the nitrogen source melamine are crucial for the successful generation of such Co-N-based materials. The obtained samples (Co-N)_n@NC were demonstrated to be highly efficient and robust catalysts for FA dehydrogenation and formylation of quinolines through transfer hydrogenation, exhibiting a very high hydrogen production rate of 16 451 mL·g_Co^-1·h^-1 for FA dehydrogenation and affording excellent yields (up to 99%), selectivity (up to 98%), and stability for transfer hydrogenation. This work may provide a promising route for the fabrication of more low-cost metal-nitrogen catalysts for green fine chemical synthesis.

Function-driven engineering of 1D carbon nanotubes and 0D carbon dots: mechanism, properties and applications

Metal-free carbonaceous nanomaterials have witnessed a renaissance of interest due to the surge in the realm of nanotechnology. Among myriads of carbon-based nanostructures with versatile dimensionality, one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) carbon dots (CDs) have grown into a research frontier in the past few decades. With extraordinary mechanical, thermal, electrical and optical properties, CNTs are utilized in transparent displays, quantum wires, field emission transistors, aerospace materials, etc. Although CNTs possess diverse characteristics, their most attractive property is their unique photoluminescence. On the other hand, another growing family of carbonaceous nanomaterials, which is CDs, has drawn much research attention due to its cost-effectiveness, low toxicity, environmental friendliness, fluorescence, luminescence and simplicity to be synthesized and functionalized with surface passivation. Benefiting from these unprecedented properties, CDs have been widely employed in biosensing, bioimaging, nanomedicine, and catalysis. Herein, we have systematically presented the fascinating properties, preparation methods and multitudinous applications of CNTs and CDs (including graphene quantum dots). We will discuss how CNTs and CDs have emerged as auspicious nanomaterials for potential applications, especially in electronics, sensors, bioimaging, wearable devices, batteries, supercapacitors, catalysis and light-emitting diodes (LEDs). Last but not least, this review is concluded with a summary, outlook and invigorating perspectives for future research horizons in this emerging platform of carbonaceous nanomaterials.

Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb₂O₅ nanoparticles/N-doped graphene hybrid anode (T-Nb₂O₅/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl₅ at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb₂O₅ nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb₂O₅/NG were improved by doping nitrogen. The T-Nb₂O₅/NG anode showed superior rate capability (68 mA h g^-1 even at 2 A g^-1) and good cycling life (106 mA h g^-1 at 0.2 A g^-1 for 200 cycles and 83 mA h g^-1 at 1 A g^-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb₂O₅/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg^-1 at a power density of 100 W kg^-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g^-1) and showed a promising application for highly efficient energy storage systems.

Hierarchical Carbon@SnS2 Aerogel with "Skeleton/Skin" Architectures as a High-Capacity, High-Rate Capability and Long Cycle Life Anode for Sodium Ion Storage

Developing high-performance electrode materials with high energy and long-term cycling stability is a hot topic and of great importance for sodium ion batteries (SIBs). In this work, a highly porous carbon/tin sulfide aerogel with a "skeleton/skin" morphology (SSC@SnS₂) has been developed and further used as a binder-free anode for SIBs. This SSC@SnS₂ electrode delivers a high specific capacity of 612 mA h g^-1 at 0.1 A g^-1, a good rate capability, and a long-term cycling stability up to 1000 times with an average Coulombic efficiency of ∼99.9%. Meanwhile, this SSC@SnS₂ aerogel also achieves a stable cycling performance even at a high current density up to 5.0 A g^-1. The fast-yet-stable sodium ion storage performance of the prepared SSC@SnS₂ aerogel can be ascribed to the reasons that (i) the carbon nanofiber/graphene skeleton provides unimpeded pathways for the rapid transfer of electrons; (ii) thin SnS₂ skin with nonaggregated morphology can provide a great number of active sites for sodium ion storage; (iii) the porous structure of the SSC@SnS₂ aerogel ensures a rapid penetration of electrolyte and can further accommodate the volume expansion of active SnS₂ nanoflakes; and (iv) the intermediate product of Na₁₅Sn₄ alloy contributes greatly to the sodium ion storage performance of the SSC@SnS₂ aerogel. The excellent electrochemical performances coupling with the unique structural features of this SSC@SnS₂ aerogel make it a promising anode candidate for SIBs.

Metal organic framework-derived CoPS/N-doped carbon for efficient electrocatalytic hydrogen evolution

Electrocatalytic hydrogen evolution has attracted a great deal of attention due to the urgent need for clean energy. Herein, we demonstrate the synthesis of ternary pyrite-type cobalt phosphosulphide (CoPS) nanoparticles supported on a nitrogen-doped carbon matrix, CoPS/N-C, through carbonization and subsequent phosphosulfurization of Co-based zeolitic imidazolate frameworks (ZIF-67), as promising hydrogen evolution reaction (HER) electrocatalysts in both acidic and alkaline solutions. The polyhedral structure of ZIF-67 can be well maintained in the as-prepared CoPS/N-C nanocomposites. In particular, CoPS/N-C provides a geometric catalytic current density of -10 mA cm-2 at overpotentials of -80 and -148 mV vs. a reversible hydrogen electrode (RHE) and a Tafel slope of 68 and 78 mV dec-1 in 0.5 M H2SO4 and 1 M KOH, respectively, which is superior to most of the transition metal phosphosulfide materials. This MOF-derived synthesis of a transition metal phosphosulfide supported heteroatom-doped carbon matrix provides a promising opportunity for the development of highly efficient electrocatalysts for renewable energy devices.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.

Double-shelled hollow mesoporous silica nanospheres as an acid–base bifunctional catalyst for cascade reactions

Double-shelled hollow mesoporous silica nanospheres as an acid–base bifunctional catalyst for cascade reactions.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.

Fabrication of a TiO2 trapped meso/macroporous g-C3N4 heterojunction photocatalyst and understanding its enhanced photocatalytic activity based on optical simulation analysis

The enhanced photocatalytic performance of a TiO₂ nanoparticle trapped meso/macroporous g-C₃N₄ heterojunction photocatalyst is strongly related to its enhanced light absorption as revealed by optical simulation.