To overcome the shuttle effect in Li–S batteries, novel biomimetic molecule catalysts are synthesized by grafting hemin molecules to three functionalized carbon nanotube systems (CNTs–COOH, CNTs–OH, and CNTs–NH2). The Li–S battery using the CNTs–COOH@hemin cathode exhibits the optimal initial specific capacity (1637.8 mAh g−1) and cycle durability (up to 1800 cycles). Various in situ characterization techniques, such as Raman spectroscopy, Fourier‐transform infrared reflection absorption spectroscopy, and UV–vis spectroscopy, combined with density functional theory computations are used to investigate the structure–reactivity correlation and the working mechanism in the Li–S system. It is demonstrated that the unique structure of the CNTs‐COOH@hemin composite with good conductivity and adequate active sites resulting from molecule catalyst as well as the strong absorption to polysulfides entrapped by the coordinated Fe(III) complex with FeO bond enables the homogeneous dispersion of S, facilitates the catalysis and conversion of polysulfides, and improves the battery's performance.
The sluggish reaction
kinetics at the cathode/electrolyte interface
of lithium–sulfur (Li–S) batteries limits their commercialization.
Herein, we show that a dual-regulation system of iron phthalocyanine
(FePc) and octafluoronaphthalene (OFN) decorated on graphene (Gh),
denoted as Gh/FePc+OFN, accelerates the interfacial reaction kinetics
of lithium polysulfides (LiPSs). Multiple in situ spectroscopy techniques and ex situ X-ray photoelectron
spectroscopy combined with density functional theory calculations
demonstrate that FePc acts as an efficient anchor and scissor for
the LiPSs through Fe···S coordination, mainly facilitating
their liquid–liquid transformation, whereas OFN enables Li-bond
interaction with the LiPSs, accelerating the kinetics of the liquid–solid
nucleation and growth of Li2S. This dual-regulation system
promotes the smooth conversion reaction of sulfur, thereby improving
the battery performance. A Gh/FePc+OFN-based Li–S cathode delivered
an ultrahigh initial capacity of 1604 mAh g–1 at
0.2 C, with an ultralow capacity decay rate of 0.055% per cycle at
1 C over 1000 cycles.
The
complicated reactions at the cathode–electrolyte interface
in Li–S batteries are a large barrier for their successful
commercialization. Herein, we developed a molecular design strategy
and employed three small molecules acting as interfacial mediators
to the cathodes of Li–S batteries. The theoretical calculation
results show that the incorporation of tris(4-fluorophenyl)phosphine
(TFPP) has a strong binding performance. The experimental results
demonstrate that the strong chemical interactions between polysulfides
and the F, P atoms in TFPP not only modify the kinetics of the electrochemical
processes in the electrolyte but also promote the formation of short-chain
clusters (Li2S
x
, x = 1, 2, 3, and 4) at the interface during the charge–discharge
process. As a result, an optimized electrode exhibits a low capacity
decay rate of 0.042% per cycle when the current rate is increased
to 5 C over 1000 cycles.
Water splitting is considered to be a very promising alternative to greenly produce hydrogen, and the key to optimizing this process is the development of suitable electrocatalysts. Here, a sacrificial‐counter‐electrode method to synthesize a MoS
x
/carbon nanotubes/Pt catalyst (0.55 wt% Pt loading) is developed, which exhibits a low overpotential of 25 mV at a current density of 10 mA cm
−2
, a low Tafel slope of 27 mV dec
−1
, and excellent stability under acidic conditions. The theory calculations and experimental results confirm the high hydrogen evolution activity that is likely due to the fact that the S atoms in MoS
x
can be substituted with O atoms during a potential cycling process when using Pt as a counter‐electrode, where the O atoms act as bridges between the catalytic PtO
x
particles and the MoS
x
support to generate a MoS
x
–O–PtO
x
structure, allowing the Pt atoms to donate more electrons thus facilitating the hydrogen evolution reaction process.
Lithium–sulfur (Li–S) batteries are receiving intense interest owing to their high energy densities, cost effectiveness, and the natural abundance of sulfur.
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