No abstract

The shuttle effect hinders the practical application of lithium-sulfur (Li-S) batteries due to the poor affinity between a substrate and Li polysulfides (LiPSs) and the sluggish transition of soluble LiPSs to insoluble Li2S or elemental S. Here, we report that Ni hexatomic clusters embedded in a nitrogen-doped three-dimensional (3D) graphene framework (Ni-N/G) possess stronger interaction with soluble polysulfides than that with insoluble polysulfides. The synthetic electrocatalyst deployed in the sulfur cathode plays a multifunctional role: (i) selectively adsorbing the polysulfides dissolved in the electrolyte, (ii) expediting the sluggish liquid-solid phase transformations at the active sites as electrocatalysts, and (iii) accelerating the kinetics of the electrochemical reaction of multielectron sulfur, thereby inhibiting the dissolution of LiPSs. The constructed S@Ni-N/G cathode delivers an areal capacity of 9.43 mAh cm-2 at 0.1 C at S loading of 6.8 mg cm-2, and it exhibits a gravimetric capacity of 1104 mAh g-1 with a capacity fading rate of 0.045% per cycle over 50 cycles at 0.2 C at S loading of 2.0 mg cm-2. This work opens a rational approach to achieve the selective adsorption and expediting of polysulfide transition for the performance enhancement of Li-S batteries.

The biggest obstacles of putting lithium−sulfur batteries into practice are the sluggish redox kinetics of polysulfides and serious "shuttle effect" under high sulfur mass loading and lean-electrolyte conditions. Herein, Fe 3 C/Fe 3 N@nitrogen-doped carbon nanotubes (NCNTs) as multifunctional sulfur hosts are designed to realize high-areal-capacity Li−S batteries. The Fe 3 N and Fe 3 C particles attached to NCNT can promote the conversion of polysulfides. Besides, NCNT can not only enhance the chemisorption of polysulfides but also increase the special surface area and electrical conductivity by constructing a three-dimensional skeleton network. Integrating the merits of high electrical conductivity, high catalytic activity, and strong chemical binding interaction with lithium polysulfides (LiPSs) to achieve in situ anchoring conversion, the Fe 3 C/Fe 3 N@NCNT multifunctional hosts realize high sulfur mass loading and accelerate redox kinetics. The novel Fe 3 C/Fe 3 N@NCNT/S composite cathode exhibits steady cycle ability and a high areal capacity of 9.10 mAh cm −2 with a sulfur loading of 13.12 mg cm −2 at 2.20 mA cm −2 after 50 cycles.

Electro- and photocatalytic hydrogen evolution reaction (e-HER and p-HER) are two promising strategies to produce green hydrogen fuel from water. High intrinsic activity, sufficient active sites, fast charge-transfer capacity, and good optoelectronic properties must be taken into consideration simultaneously in pursuit of an ideal bifunctional catalyst. Here, platinum atomic clusters embedded in defects of TiO2 nanocrystals/graphene nanosheets (Pt–T/G) are reported as a bifunctional catalyst for electro- and photocatalytic hydrogen evolution reaction (e-HER and p-HER). High activity is delivered due to the charge transfer from the other part of the catalyst to the active center (Pt2–O4–Ti x ), decreasing the activation energy of the rate-limiting step, which is revealed by synchrotron X-ray absorption spectroscopy, photoelectrochemical measurements, and simulated calculations. In regard to e-HER, it outperforms the commercial 20 wt % Pt/C catalyst by a factor of 17.5 on Pt mass basis, allowing for a 93% reduction in Pt loadings. In regard to p-HER, it achieves photocatalytic efficiency (686.8 μmol h–1) without any attenuation in 9 h.

The development of sodium-ion batteries (SIBs) is hindered by the rapid reduction in reversible capacity of carbon-based anode materials. Outside-in doping of carbonbased anodes has been extensively explored. Nickel and NiS 2 particles embedded in nitrogen and sulfur codoped porous graphene can significantly improvet he electrochemical performance. Herein abuilt-in heteroatom "self-doping" of albumen-derived graphenef or sodium storage is reported. The built-in sulfur and nitrogen in albumen act as the doping source during the carbonization of proteins. The sulfur-rich proteinsi na lbumen can also guide the doping and nucleation of nickel sulfide nanoparticles. Additionally,t he porous architecture of the carbonized proteins is achieved through removable KCl/NaCl salts (medium) under high-temperature melting conditions. During the carbonizationp rocess, nitrogen can also reduce the carbonization temperature of thermally stable carbon materials. In this work, the NS-graphene delivered as pecific capacity of 108.3 mAh g À1 after 800 cycles under ac onstant current densityo f5 00 mA g À1 . In contrast, the Ni/NiS 2 /NS-graphenem aintained as pecific capacityof134.4 mAh g À1 ;thus the presence of Ni/NiS 2 particles improved the electrochemicalp erformanceo fthe wholec omposite.