High‐Entropy Materials for Gas Sensing in Extreme Environments: Mechanisms, Performance Regulation, and Design Strategies

ABSTRACT Gas sensors are increasingly required for distributed and unattended applications, where low power consumption, reliable calibration, and environmental robustness are as important as sensitivity. Temperature extremes, high humidity, chemically aggressive atmospheres, and coexisting gases can perturb adsorption/desorption, surface‐reaction kinetics, carrier transport, interfacial barriers, and long‐term baseline stability. This Review critically assesses high‐entropy materials (HEMs) as compositionally tunable platforms for gas sensing under such conditions. Structurally validated high‐entropy oxides and alloys, together with emerging high‐entropy‐derived or compositionally complex MXene‐, MOF‐, carbonaceous, and non‐oxide systems, provide diverse design spaces for regulating local coordination, defect chemistry, active sites, and interfacial electronic structure. An application‐oriented framework is established to link HEM design with gas‐sensing mechanisms, evidence‐based evaluation, and extreme‐environment operation. Particular emphasis is placed on distinguishing high‐entropy‐design‐related contributions from conventional multicomponent, element‐specific, defect‐mediated, and interfacial effects. Performance and reliability are considered across high‐temperature, high‐humidity/marine, low‐temperature/cold‐chain, and corrosive/poisoning environments, with material stability and sensing‐signal stability evaluated separately. Environment‐specific criteria are discussed for thermal and humidity cycling, mixed‐gas interference, recovery completeness, long‐term drift, and multi‐stressor operation. Overall, this Review advances mission‐oriented strategies for reliable and environment‐tolerant high‐entropy gas sensors.