Riming Hu

Abstract High‐entropy materials (HEMs) have great potential for energy storage and conversion due to their diverse compositions, and unexpected physical and chemical features. However, high‐entropy atomic layers with fully exposed active sites are difficult to synthesize since their phases are easily segregated. Here, it is demonstrated that high‐entropy atomic layers of transition‐metal carbide (HE‐MXene) can be produced via the selective etching of novel high‐entropy MAX (also termed M n +1 AX n ( n = 1, 2, 3), where M represents an early transition‐metal element, A is an element mainly from groups 13–16, and X stands for C and/or N) phase (HE‐MAX) (Ti 1/5 V 1/5 Zr 1/5 Nb 1/5 Ta 1/5 ) 2 AlC, in which the five transition‐metal species are homogeneously dispersed into one MX slab due to their solid‐solution feature, giving rise to a stable transition‐metal carbide in the atomic layers owing to the high molar configurational entropy and correspondingly low Gibbs free energy. Additionally, the resultant high‐entropy MXene with distinct lattice distortions leads to high mechanical strain into the atomic layers. Moreover, the mechanical strain can efficiently guide the nucleation and uniform growth of dendrite‐free lithium on HE‐MXene, achieving a long cycling stability of up to 1200 h and good deep stripping–plating levels of up to 20 mAh cm −2 .

OH.

Abstract Although lithium–sulfur (Li–S) batteries are one of the most promising energy storage devices owing to their high energy densities, the sluggish reaction kinetics and severe shuttle effect of the sulfur cathodes hinder their practical applications. Here, single atom zinc implanted MXene is introduced into a sulfur cathode, which can not only catalyze the conversion reactions of polysulfides by decreasing the energy barriers from Li 2 S 4 to Li 2 S 2 /Li 2 S but also achieve strong interaction with polysulfides due to the high electronegativity of atomic zinc on MXene. Moreover, it is found that the homogenously dispersed zinc atoms can also accelerate the nucleation of Li 2 S 2 /Li 2 S on MXene layers during the redox reactions. As a result, the sulfur cathode with single atom zinc implanted MXene exhibits a high reversible capacity of 1136 mAh g −1 . After electrode optimization, a high areal capacity of 5.3 mAh cm −2 , high rate capability of 640 mAh g −1 at 6 C, and good cycle stability (80% capacity retention after 200 cycles at 4 C) can be achieved.

The active sites of Fe–N–C catalysts are nitrogen coordinated iron atoms, FeN<italic>x</italic>(<italic>x</italic> = 1–5), that have five possible coordination numbers, corresponding to different ORR activities and PEMFC performances.