Lithium–sulfur batteries (LSBs) are widely regarded as promising next-generation batteries due to their high theoretical specific capacity and low material cost. However, the practical applications of LSBs are limited by the shuttle effect of lithium polysulfides (LiPSs), electronic insulation of charge and discharge products, and slow LiPSs conversion reaction kinetics. Accordingly, the introduction of catalysts into LSBs is one of the effective strategy to solve the issues of the sluggished LiPS conversion. Because of their nearly 100% atom utilization and high electrocatalytic activity, single-atom catalysts (SACs) have been widely used as reaction mediators for LSBs’ reactions. Excitingly, the SACs with asymmetric coordination structures have exhibited intriguing electronic structures and superior catalytic activities when compared to the traditional M–N₄ active sites. In this review, we systematically describe the recent advancements in the installation of asymmetrically coordinated single-atom structure as reactions catalysts in LSBs, including asymmetrically nitrogen coordinated SACs, heteroatom coordinated SACs, support effective asymmetrically coordinated SACs, and bimetallic coordinated SACs. Particularly noteworthy is the discussion of the catalytic conversion mechanism of LiPSs spanning asymmetrically coordinated SACs. Finally, a perspective on the future developments of asymmetrically coordinated SACs in LSB applications is provided.

MXene as a novel two-dimensional transition metal carbides, nitrides or carbonitrides has the excellent metal conductivity, high carrier mobility, and surface-terminated groups regulated band structure. It can be thus used as a cocatalyst in photocatalytic material systems to improve the photocatalytic properties. This review represented recent research progress on the controllable construction of MXene-based composites with zero-dimensional, one-dimensional, two-dimensional, and three-dimensional semiconductor photocatalytic materials and its applications in the photocatalytic fields (i.e., pollutant removal, hydrogen production, CO₂ reduction, and nitrogen fixation). Also, the construction methods and photocatalytic enhancement mechanisms of two-dimensional MXene-based composite photocatalysts were given. In addition, the future research directions of MXene-based composite photocatalysts were also prospected.

A series of bimetallic nickel cobalt sulfides with hierarchical micro/nano architectures were fabricated via a facile synthesis strategy of bimetallic micro/nano structure precursor construction-anion exchange via solvothermal method. Among the nickel cobalt sulfides with different Ni/Co contents, the coral-like Ni_1.01Co_1.99S₄ (Ni/Co, 1/2) delivers ultrafast and stable Na-ion storage performance (350 mAh·g⁻¹ after 1, 000 cycles at 1 A·g⁻¹ and 355 mAh·g⁻¹ at 5 A·g⁻¹). The remarkable electrochemical properties can be attributed to the enhanced conductivity by co-existence of bimetallic components, the unique coral-like micro/nanostructure, which could prevent structural collapse and self-aggregation of nanoparticles, and the easily accessibility of electrolyte, and fast Na⁺ diffusion upon cycling. Detailed kinetics studies by a galvanostatic intermittent titration technique (GITT) reveal the dynamic change of Na⁺ diffusion upon cycling, and quantitative kinetic analysis indicates the high contribution of pseudocapacitive behavior during charge–discharge processes. Moreover, the ex-situ characterization analysis results further verify the Na-ion storage mechanism based on conversion reaction. This study is expected to provide a feasible design strategy for the bimetallic sulfides materials toward high performance sodium-ion batteries.