High-entropy single-atom catalysts (HESACs) represent a paradigm shift in electrocatalyst design, integrating the atomic efficiency of single-atom catalysts (SACs) with the configurational entropy of high-entropy alloys (HEAs). Unlike conventional SACs, HESACs maintain well-defined coordination geometries while leveraging multi-element electronic reconstruction to mitigate the limitations of single metal sites in complex multistep reactions. This review outlines the fundamentals, design principles, and recent synthetic advancements in HESACs, including spatial confinement, laser planting, selective etching, movable-type printing, and pyrolysis, alongside advanced characterization techniques. Performance in key applications, such as HER, ORR/OER, NO₃RR, and Li–S batteries, demonstrates that entropy-driven electronic modulation and multi-site synergy are central to their exceptional activity and durability. Finally, we discuss challenges and future pathways for translating HESACs from fundamental discoveries to practical electrocatalytic applications.

The oxygen evolution reaction (OER) suffers from low intrinsic activity, poor oxidative stability, and insufficient electrical conductivity, which severely limit the practical deployment of non-precious metal electrocatalysts. To overcome these obstacles, we designed an MXene@Co(OH)₂ hybrid supported on carbon cloth (MXene@Co(OH)₂/CC) using a straightforward electrodeposition and vacuum drying method. Strong interfacial interactions between MXene and Co(OH)₂ boost charge transfer, create abundant accessible active sites, and reinforce structural integrity under OER working conditions. Consequently, the MXene@Co(OH)₂/CC electrode requires only 261 mV to achieve 10 mA·cm⁻² and shows a Tafel slope of 61.7 mV·dec⁻¹, and retains excellent performance for more than 1100 h. Beyond delivering a highly efficient and low-cost OER catalyst, this work also provides a valuable paradigm for constructing well-defined heterostructured catalytic systems via interfacial engineering.

Molecular catalysts with well-defined single atom sites and coordination environments exhibit significant potential as oxygen reduction electrocatalysts, but suffering from the activity and stability issues. Herein, the ultrathin carbon shell supported FePc molecule electrocatalysts (FePc/TA-ONG-N), featuring with a direct oxygen bridging between FePc and carbon substrate, were designed and synthesized. The direct connection with oxygen atom on carbon substrate, certified by the Fourier transform infrared spectroscopy (FTIR) and extended X-ray absorption fine structure (EXAFS), can remarkably enhance the interaction and facilitate electron transfer from Fe, leading to an improved activity by reducing adsorption strength of intermediate species through lowering the d-band center position. The resultant half-wave potential of 0.902 V together with a Tafel slope of 23.64 mV·dec⁻¹ is superior to Pt/C and control samples. Such catalyst holds a promise as air-cathode electrocatalyst in Zn-air battery with excellent operation stability exceeding 80 h. The density functional theory (DFT) calculations and molecular dynamic simulations unveiled that the O-bridge can effectively stabilize the FePc molecule and function as electron buffer to donate/gain electrons to/from Fe atom during the adsorption of oxygenates. The current findings are insightful for developing molecular catalysts with high performance through substrate engineering and axial coordination.