Amid the global push for energy transition and carbon neutrality, constructing highly active electrocatalysts is essential to overcome the challenges of energy conversion and storage. N-doped carbon substrate-based single-atom catalysts (SA/NCs), with a clear reaction center, robust stability, and excellent electrical conductivity, have emerged as a key focus in electrocatalytic research. However, traditional SA/NCs mainly exhibit a porphyrin-like planar M–N₄ configuration, with a symmetrical charge distribution that limits their catalytic efficiency. Recently, the development of edge-rich NC substrates to anchor edge-type metal sites (eSA/NCs) can induce charge rearrangement and promote the exposure of active sites, leading to significantly enhanced electrocatalytic performance. This review provides a comprehensive summary of eSA/NCs for electrocatalytic reactions. First, the synthetic strategies of eSA/NCs are classified, and the main characterization techniques are introduced. Subsequently, the performance of eSA/NCs in diverse electrocatalytic reactions is carefully discussed, with emphasis on elucidating the structure-activity relationships underpinned by edge structure. Finally, regarding the issues of controllable construction and quantitative analysis of the current NC substrates with high edge density, we have proposed feasible development directions and strategies. This work highlights the significance of edge structure contributions in enhancing the catalytic efficiency of SA/NCs and provides technical guidance for designing future high-performance electrocatalysts.

The electrochemical CO₂ reduction reaction (CO₂RR) represents a pivotal strategy for climate change mitigation and carbon neutrality by converting CO₂ into value-added chemicals under mild conditions. MXene-based single-atom catalysts (SACs) have emerged as promising systems for CO₂RR, synergistically integrating MXene’s tunable two-dimensional (2D) architecture with atomic dispersion of active sites to achieve exceptional activity, selectivity, and stability. Thus, a timely review of the recent advances is necessary to inspire further research. This review systematically summarizes the anchoring mechanisms of single atoms on MXene substrates, focusing on the principal products generated by MXene-based single-atom catalysts in CO₂ reduction reactions and the critical factors governing product selectivity. This review outlines the main strategies for optimizing MXene to enhance the performance of MXene-based SACs. Finally, conclusions and perspectives about MXene-based SACs for CO₂RR are presented. This review underscores the potential of MXene-based SACs and provides a roadmap for their future development, aiming to bridge the gap between fundamental research and industrial application in CO₂RR technologies.

Two-dimensional MXenes have great potential for gas sensing applications due to their distinct electronic structure and unique surface properties. However, low sensitivity and poor selectivity to target gas at room temperature are major shortcomings of MXene materials. In this study, PdCl₂ was used to decorate Pd single atoms (Pd_SA) on Ti₃C₂ nanosheet (Ti₃C₂/Pd_SA). The Pd²⁺ was directly reduced (in-situ) into a Pd_SA due to abundant Ti vacancies and the inherent reducing ability of Ti₃C₂ MXene. The Ti₃C₂/Pd_SA sensor exhibited the highest response of 0.289 to 1 ppm NO₂, which is 28.9 and 7.8 times higher over pristine Ti₃C₂ and Pd nanoparticles (Pd_nano)-decorated on Ti₃C₂ (Ti₃C₂/Pd_nano), respectively. Simultaneously, the Ti₃C₂/Pd_SA sensor possessed an ultralow detection limit (10 ppb) and excellent selectivity towards NO₂. The enhanced gas sensing mechanism of Ti₃C₂/Pd_SA was investigated in detail through the activation energy calculation, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and density functional theory (DFT) studies. The rich active sites, chemical sensitization effect, and NO₂ adsorption enhancement resulting from the Pd single atoms in Ti₃C₂/Pd_SA significantly boosted sensing performance. This work can provide new insights and guidelines for fabricating highly effective NO₂ sensors operated at room temperature.