Lithium–sulfur (Li–S) batteries are regarded as promising secondary energy storage devices for their high energy density and low cost. The electrochemical performance of Li–S batteries is mainly ...determined by the efficient and reversible conversion of lithium-polysulfides to Li2S when discharging and to S when charging. Herein, a catalytic strategy is proposed to accelerate the reversible conversion of S and the discharge products in Li–S batteries. This reversible transformation is achieved with active sites of single-atom iron on nitrogen- and sulfur-doped porous carbon (FeNSC). We prove that the synergy between atomically dispersed iron and doped sulfur accelerates the reversible electrochemical conversion reactions in Li–S batteries. The FeNSC/S hybrid cathode exhibits superior long-term cycling stability even at a high current density of 1C, with only 0.047% capacity decay per cycle over 1000 cycles. This study demonstrates a novel method for improving the conversion of polysulfides based on electrocatalysis strategies to ultimately obtain high-performance Li–S batteries.
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Two-dimensional (2D) transition-metal carbides (MXenes) are widely adopted as potential electrocatalysts for the hydrogen evolution reaction (HER) owing to their metallic conductivity, rich tunable ...surface chemistry, and atomic thickness with highly exposed active sites. Previously published theoretical results indicate that MXenes functionalized entirely with oxygen have lower ΔG
for HER. However, MXenes contain many terminal F groups on the basal plane, which is detrimental to the HER. Herein, the development of an ultrathin Ti
C
MXene nanosheet fully functionalized with oxygen is reported for the HER. The obtained oxygen-functionalized Ti
C
(Ti
C
O
) exhibits a much higher HER activity (190 mV at 10 mA cm
) than that of Ti
C
T
(T=F, OH, and O). The improved HER performance is attributed to the highly active O sites on the basal plane of Ti
C
T
MXenes. This study paves way for electrocatalytic applications of MXene materials by tuning their surface functional groups.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Potassium‐ion batteries (KIBs) are receiving increased attention due to their cost‐effective and similar energy‐storage mechanism to lithium‐ion batteries. However, the lack of appropriate electrode ...materials is still hampered for their development, which is mainly caused by the large size of the potassium ions (1.38 Å) including low structural stability and poor electrochemical redox reaction kinetics. Herein, Co3Se4 quantum dots (QD) encapsulated by N‐doped carbon (CSC) are reported as an anode material for KIBs, in which a morphology change process occurs. Benefiting from the unique uniform nanostructure reducing the ion‐diffusion length, the improved electronic conductivity, and the enhanced protective effect of N‐doped carbon (NC) alleviating volume fluctuation, the CSC demonstrates excellent electrochemical performance. The core–shell‐like CSC composite demonstrates remarkable discharge capacity (410 mA h g−1 at 0.1 A g−1 after 550 cycles, 360 mA h g−1 at 0.5 A g−1 after 3200 cycles) and excellent cyclic performance over 10 000 cycles at 1 A g−1. Density functional theory calculations show a larger reaction energy of Co3Se4 QD than bulk Co3Se4, a lower barrier of K atom migration in Co3Se4 QD than bulk Co3Se4, and also favor the intercalation reaction rather than replacement reaction. In situ X‐ray diffraction and ex situ transmission electron microscopy are further used to evaluate potassiation/depotassiation phenomena.
Co3Se4 quantum dots encapsulated by N‐doped carbon (CSC) are reported as an anode material for potassium‐ion batteries, in which a morphology change process occurs. The unique core–shell‐like‐structure anode demonstrates greatly enhanced electrochemical performance, especially long‐term cyclic performance at various current densities. Density functional theory calculations, in situ X‐ray diffraction, and ex situ transmission electron microscopy further reveal the working mechanism of the CSC anode during potassiation/depotassiation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Two‐dimensional (2D) transition‐metal carbides (MXenes) are widely adopted as potential electrocatalysts for the hydrogen evolution reaction (HER) owing to their metallic conductivity, rich tunable ...surface chemistry, and atomic thickness with highly exposed active sites. Previously published theoretical results indicate that MXenes functionalized entirely with oxygen have lower ΔGH* for HER. However, MXenes contain many terminal F groups on the basal plane, which is detrimental to the HER. Herein, the development of an ultrathin Ti3C2 MXene nanosheet fully functionalized with oxygen is reported for the HER. The obtained oxygen‐functionalized Ti3C2 (Ti3C2Ox) exhibits a much higher HER activity (190 mV at 10 mA cm−2) than that of Ti3C2Tx (T=F, OH, and O). The improved HER performance is attributed to the highly active O sites on the basal plane of Ti3C2Tx MXenes. This study paves way for electrocatalytic applications of MXene materials by tuning their surface functional groups.
S‘O’ much win with MXene: A facile method is reported to produce ultrathin Ti3C2 MXene functionalized with oxygen as an electrocatalyst for the hydrogen evolution reaction. The terminal O on the basal plane increases the number of active sites for electrocatalysis. This combined with the high surface area and conductivity enables the O‐functionalized MXene to show enhanced electrocatalytic performance for hydrogen evolution.
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Two-dimensional iron phosphorus trichalcogenide (FePS
) has attracted significant attention for its use in electricity, magnetism and optical fields due to its outstanding physical and chemical ...properties. Herein, FePS
was prepared using the chemical vapor transportation (CVT) method and then exfoliated by using fast electrochemical exfoliation. After gradient centrifugation, FePS
nanosheets with thicknesses ranging from 1.5 to 20 nm and lateral dimensions of 0.5–3 μm were obtained. By utilizing the spatial self-phase modulation (SSPM) effect, the relationships between the nonlinear refractive index and the size of the FePS
nanosheets were investigated in detail which revealed that the nonlinear refractive index can be effectively controlled by the size of the FePS
nanosheets. It is worth noting that the optimal FePS
nanosheets (3–5 layers thick and ∼1 μm in lateral dimensions) displayed the highest nonlinear refractive index of ∼10
cm
W
. This work demonstrates the potential that FePS
nanosheets have for use in nonlinear optics or nonlinear optical devices.
One of the most common problems with sulfide solid-state electrolytes is weak water stability. We report a re-sintering method to recover the ionic conductivity of argyrodite Li 5.4 PS 4.4 Cl 1.6 ...solid-state electrolyte, which has been exposed to moisture for 10 h, from 1.06 to 6.97 mS cm −1 .
One of the most common problems with sulfide solid-state electrolytes is weak water stability. We report a re-sintering method to recover the ionic conductivity of argyrodite Li
5.4
PS
4.4
Cl
1.6
...solid-state electrolyte, which has been exposed to moisture for 10 h, from 1.06 to 6.97 mS cm
1
.
One of the most common problems with sulfide solid-state electrolytes is weak water stability.
Potassium ion batteries (KIBs), because of their low price, may exhibit advantages over lithium ion batteries as potential candidates for large-scale energy storage systems. However, owing to the ...large ionic radii of K-ions, it is challenging to find a suitable intercalation host for KIBs and thus the rechargeable KIB electrode materials are still largely unexplored. In this work, a reticular V2O5·0.6H2O xerogel was synthesized via a hydrothermal process as a cathode material for rechargeable KIBs. Compared with the orthorhombic crystalline V2O5, the hydrated vanadium pentoxide (V2O5·0.6H2O) exhibits the ability of accommodating larger alkali metal ions of K+ because of the enlarged layer space by hosting structural H2O molecules in the interlayer. By intercalation of H2O into the V2O5 layers, its potassium electrochemical activity is significantly improved. It exhibits an initial discharge capacity of ∼224.4 mA h g–1 and a discharge capacity of ∼103.5 mA h g–1 even after 500 discharge/charge cycles at a current density of 50 mA g–1, which is much higher than that of the V2O5 electrode without structural water. Meanwhile, X-ray diffraction and X-ray photoelectron spectroscopy combined with energy dispersive spectroscopy techniques are carried out to investigate the potassiation/depotassiation process of the V2O5·0.6H2O electrodes, which confirmed the potassium intercalation storage mechanisms of this hydrated material. The results demonstrate that the interlayer-spacing-enlarged V2O5·0.6H2O is a promising cathode candidate for KIBs.
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•The seft-template of C3N4 ensures the efficient doping of the functional elements.•The tuning effect of template and the synergy effect enhance ORR activities.•High performance: Onset potential of ...0.93 V and half-wave potential of 0.85 V.•DFT reveals the synergistic effect of the N and P dopants.
The performance of metal-free oxygen reduction reaction (ORR) electrocatalysts are far from satisfactory, thus impeding their real world application. Herein, we present a C3N4 self-templating method to construct a P and N co-doped porous carbon nanosheets with high ORR performance. The conbination of the templating effect and the synergy effect direved from N, P co-doping is revealed of utmost importance towards ORR. The optimized catalyst represents an outstanding ORR performance with an onset potential of 0.93 V and half-wave potential of 0.85 V, comparable to those of commercial Pt/C electrocatalysts (1.04 V, 0.84 V).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Carbazolic conjugated microporous polymer (C-CMP) is obtained via straightforward carbazole-based oxidative coupling polymerization. C-CMP exhibits high porosity and a specific surface area of 1137 ...m2 g–1, and it is thermally stable to 600 °C in nitrogen. C-CMP is shown to be a highly effective heterogeneous photocatalyst for a wide range of reactions, including the oxidative coupling of primary amines, aerobic dehydrogenation of nonactive secondary amine substrates such as pharmaceutically relevant nitrogen heterocycles, and selective oxidation of sulfide using molecular oxygen and visible light. This work highlights the potential of developing photoactive N-containing CMPs as a highly stable, molecularly tunable, reusable, and metal-free visible light photocatalysts for a wide variety of organic transformations.
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