[en] Graphical abstract: C₃N₄/rGO aerogels were synthesized through hydrothermal reaction, which exhibit strong absorbtion to lithium polysulfides and enhance the longevity of sulfur electrode. Display Omitted -- Highlights: •C₃N₄/rGO aerogels with unique nanostructure were synthesized by simple solvothermal methods. •The interconnected aerogel provides both physical barrier and chemical absorption to deter the dissolution of polysulfides into the electrolyte. •It has been identified that the C₃N₄/rGO-sulfur cathode with 1:2 mass ratio of C₃N₄ and rGO (CG12) exhibited the optimized performance. -- Abstract: Lithium-sulfur (Li-S) batteries have been attractive alternatives to lithium-ion (Li-ion) batteries due to the high theoretical capacity of sulfur cathode. However, the polysulfide shuttling effect is detrimental to the long-term cycling stability. Chemically absorptive host materials provide an effective way to mitigate the dissolution of lithium polysulfide. Carbon nitride (C₃N₄) is one of the effective host materials with strong interaction with polysulfide species. The low electronic conductivity, however, is unfavorable for high sulfur utilization. In this work, we report the controlled synthesis of porous, well-interconnected C₃N₄/reduced graphene oxide (rGO) aerogels as hybrid sulfur host using a simple hydrothermal reaction followed by freeze-drying, which combines the structural merits of both highly conductive rGO networks and chemically active C₃N₄. By further tuning the structure/morphology and the ratio between C₃N₄ and rGO, we have demonstrated the C₃N₄/rGO composites with optimized 1:2 ratio of C₃N₄:rGO (termed as CG12) exhibits not only very high sulfur utilization but also excellent rate capability compared to other C₃N₄/rGO composites, pure rGO, and C₃N₄. The compositionally and structurally tailored CG12 also shows stable cycling performance over 400 cycles with a low decay rate of 0.09% per cycle.

[en] Delicately engineering well-defined noble metal aerogels with favorable structural and compositional features is of vital importance for wide applications. Here, we reported a one-pot and facile method for synthesizing core–shell PdPb@Pd hydrogels/aerogels with multiply-twinned grains and an ordered intermetallic phase using sodium hypophosphite as a multifunctional reducing agent. Due to the accelerated gelation kinetics induced by increased reaction temperature and the specific function of sodium hypophosphite, the formation of hydrogels can be completed within 4 h. As a result, owing to their unique porous structure and favorable geometric and electronic effects, the optimized PdPb@Pd aerogels exhibit enhanced electrochemical performance towards ethylene glycol oxidation with a mass activity of 5.8 times higher than Pd black.

[en] SnO₂ is a promising material for both Li-ion and Na-ion batteries owing to its high theoretical capacities. Unfortunately, the electrochemical performance of SnO₂ is unsatisfactory because of the large volume change that occurs during cycling, low electronic conductivity of inactive oxide matrix, and poor kinetics, which are particularly severe in Na-ion batteries. Herein, ultra-fine SnO₂ nanocrystals anchored on a unique three-dimensional (3D) porous reduced graphene oxide (rGO) matrix are described as promising bifunctional electrodes for Li-ion and Na-ion batteries with excellent rate capability and long cycle life. Ultra-fine SnO₂ nanocrystals of size ∼6 nm are well-coordinated to the graphene sheets that comprise the 3D macro-porous structure. Notably, superior rate capability was obtained up to 3 C (1/n C is a measure of the rate that allows the cell to be charged/discharged in n h) for both batteries. In situ X-ray diffractometry measurements during lithiation (or sodiation) and delithiation (or desodiation) were combined with various electrochemical techniques to reveal the real-time phase evolution. This critical information was linked with the internal resistance, ion diffusivity ($D_{L{i}^{+}}$ and $D_{N{a}^{+}}$), and the unique structure of the composite electrode materials to explain their excellent electrochemical performance. The improved capacity and superior rate capabilities demonstrated in this work can be ascribed to the enhanced transport kinetics of both electrons and ions within the electrode structure because of the well-interconnected, 3D macro-porous rGO matrix. The porous rGO matrix appears to play a more important role in sodium-ion batteries (SIBs), where the larger mass/radius of Na-ions are marked concerns. .

[en] Graphical abstract: MOF-derived hierarchically porous nitrogen-doped carbon nanostructures were synthesized, which exhibited the enhanced electrochemical performance for oxygen reduction reaction. - Highlights: • Isoreticular metal-organic frameworks were synthesized by simple solvothermal methods. • The hierarchically porous nitrogen-doped carbon materials were prepared through direct carbonization of metal-organic frameworks. • The obtained electrocatalyst exhibited excellent activity for oxygen reduction reaction. - Abstract: The hierarchically porous nitrogen-doped carbon materials, derived from nitrogen-containing isoreticular metal-organic framework-3 (IRMOF-3) through direct carbonization, exhibited excellent electrocatalytic activity in alkaline solution for oxygen reduction reaction (ORR). This high activity is attributed to the presence of high percentage of quaternary and pyridinic nitrogen, the high surface area as well as good conductivity. When IRMOF-3 was carbonized at 950 °C (CIRMOF-3-950), it showed four-electron reduction pathway for ORR and exhibited better stability (about 78.5% current density was maintained) than platinum/carbon (Pt/C) in the current durability test. In addition, CIRMOF-3-950 presented high selectivity to cathode reactions compared to commercial Pt/C.