A conductive and ordered macroporous structure design of titanium oxide-based catalytic cathode for lithium-sulfur batteries.

The application of lithium-sulfur (Li-S) batteries is hindered by the insulating characteristic of sulfur and slow reaction kinetics of lithium polysulfides. Here, we propose a three-dimensionally ordered macroporous (3DOM) structured conductive polar Ta-doped TiO2framework with supported Co active site (CoTa@TiO2) to enhance the conversion kinetics of polysulfides. The 3DOM structure serves as an efficient sulfur host for the active sulfur through abundant pores and adsorption site. At the same time, the macropores can buffer the volume expansion of sulfur and enlarged mass transfer. The strong electrostatic attraction between Ti-O bond and polysulfide also promotes the adsorption of polysulfides. Moreover, the doped-Ta improves the conductivity of TiO2by narrowing the band gap, whereas the supported Co can accelerate the catalytic transformation. Benefited from advanced structural design and synergistic effect of Co and Ta doped TiO2,the Li-S cell with 3DOM CoTa@TiO2cathode exhibits an impressive areal capacity of 3.4 mAh cm-2under a high sulfur loading of 5.1 mg cm-2. This work provides an alternative strategy for the development of carbon-based cathode materials for Li-S batteries.

Nanoscale melamine-based porous organic frameworks as host material for efficient polysulfides chemisorption in lithium-sulfur batteries.

In order to improve the electrochemical capacity of lithium-sulfur batteries (LiSBs), it is necessary to introduce the porous organic frameworks with well-defined hetero atom species in cathode. In this work, porous nanomaterials with ultra-high nitrogen containing and adjustable porosity named Schiff-based networks (SNWs) were selected as potential candidate for sulfur host in LiSBs. Two SNW samples have been constructed by reacting melamine with phenyl or biphenyl dialdehydes through microwave-assisted method, respectively. The high BET surface area provided sufficient room to impregnate sulfur and mitigated volume changes during the cycling performance. Besides, the high density and homogeneous distribution of pyridinic-N and aminic-N in SNW nanoparticles can cooperatively form lithium polysulfides (LiPSs) chemisorption via enhanced Li+-N interactions to effectively suppressed the 'shuttle effect'. Attributed to its structural superiorities, SNW/S cathode demonstrates excellent electrochemical performance in LiSBs. In particular, SNW-2/S cathode delivers an excellent cyclability with a specific capacity of 620 mAh · g-1 after 500 cycles at 0.5 C, counting with a low capacity fading of 0.0508% per cycle. This work highlights the importance of rational design for effective LiPSs chemisorption and pioneers a facile strategy for developing suitable sulfur host materials towards high-performance LiSBs.

Surface-engineered cobalt nitride composite as efficient bifunctional oxygen electrocatalyst.

Efficient and low-cost bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the practical application of rechargeable metal-air batteries. In this work, we developed an efficient cobalt nitride hybrid bifunctional electrocatalyst, which consists of sulfur-doped and mildly oxidized Co5.47N nanoparticles supported on nitrogen-doped reduced graphene oxide sheet (O-S-Co5.47N@N-RGO). The composite exhibits good ORR-OER catalytic activity and excellent stability as well. It delivers an ORR half-wave potential of 0.82 V and an over-potential of 380 mV for OER at 10 mA cm-2 in 0.1 M KOH electrolyte. Density functional theory calculations indicate that the ORR activity of the composite might have originated from the Co-N4 site in the RGO sheet, whereas the surface Co sites on O-S-Co5.47N crystal are responsible for its OER activity. The facile preparation method and insight into the ORR-OER active sites reported in this study advances the development of high-performance bifunctional oxygen electrocatalyst.