High‐Entropy Engineering and External Magnetic Field Modulation Synergistically Enhance the H 2 S Sensing Performance of Rare‐Earth Perovskite Ferrites

ABSTRACT High‐performance gas sensors with extreme sensitivity and rapid response kinetics are fundamental to sub‐ppm H 2 S detection, which is crucial for environmental monitoring and industrial safety. However, most conventional rare‐earth ferrites have relatively sluggish responses at low concentrations because of thermodynamic and kinetic constraints and inherently high surface reaction barriers. Herein, a high‐entropy perovskite oxide with the composition (Gd 0.2 Tb 0.2 Dy 0.2 Ho 0.2 Er 0.2 )FeO 3 was designed and synthesized using a wet‐chemical method. The incorporation of multiple principal elements induced strong local lattice distortion and generated abundant chemically heterogeneous active sites. Furthermore, the application of an external magnetic field significantly optimized electron transfer pathways and accelerated the surface redox reaction kinetics. Our results reveal that the synergistic coupling between high‐entropy‐induced structural distortion and weak magnetic field modulation breaks the traditional response‐recovery trade‐off, yielding a 6‐fold sensitivity enhancement over conventional counterparts, an ultrafast 1.72 s recovery time, and an H 2 S detection limit of 0.5 ppm. This strategy, which integrates local coordination reconstruction with spin‐state intervention, is expected to be widely applicable to the development of next‐generation intelligent sensing systems.