Variable infrared emissive materials and devices are effective for the dynamic modulation of infrared radiation. Herein, a new idea of dynamic emissivity modulation based on the hydrogen‐induced metal–insulator phase transition from metallic yttrium (or yttrium dihydride) to dielectric yttrium trihydride is proposed, and infrared gasochromic devices based on yttrium/rhodium metal thin films and infrared‐transparent covers are developed. By alternately injecting 4% hydrogen–argon gas mixture and air into the gasochromic device, the infrared emissivity of the device is dynamically modulated reversibly. The emissivity changes in the 340‐nm‐yttrium/6‐nm‐rhodium device are 0.25 and 0.39 in the 3–5 and 7.5–14 µm atmospheric window regions, respectively, and the response time is <40 s. The emissivity change is affected by the surface morphology and thickness of the yttrium/rhodium film. Moreover, the infrared gasochromic device operates effectively over 100 cycles, and subsequent failure is attributed to oxidation of the yttrium film. The proposed device is easily enlarged and patterned because of its simple structure, thereby indicating that such metal thin films provide a new material platform for dynamic infrared radiation modulation, which has great application prospects in the fields of adaptive thermal camouflage, smart thermal management, and infrared information display.

Dynamic infrared emissivity (DIE) regulators, which can efficiently modulate infrared radiation beyond vision, have emerged as an attractive technology in energy and information fields. However, current DIE regulators are usually visibly opaque, which limits their applications involving broad-spectrum requirements or multispectral compatibility. Therefore, it is necessary to propose new DIE mechanism and develop the desirable fully transparent DIE regulators for dynamically regulating infrared emissivity and solar spectral properties independently, although highly challenging. Here, we demonstrate DIE regulators based on a novel DIE mechanism with high visible transparency (84.7%), large emissivity regulation (0.51 in 3–5 µm, 0.42 in 7.5–13 µm), fast response (< 600 ms), and long cycle life (> 104 cycles). This excellent performance is achieved by the reversible injection/extraction of electrons into/from aluminum-doped zinc oxide (AZO) nanocrystals to modulate infrared plasmonic in a capacitive-type device, and the DIE regulation is attributed to variation of carrier concentration in the depletion layer near the surface of AZO nanocrystals. This novel DIE regulation method and fully transparent DIE regulators provide great opportunities for the on-demand smart thermal management of buildings and spacecrafts, multispectral display and adaptive camouflage, and may in other infrared radiation related technologies.

Tunable emissivity technology is promising for the dynamic regulation of infrared radiation. Herein, infrared electrochromic devices based on thin metal films that operate via a novel hydrogen‐induced metal–insulator transition are demonstrated. The use of thin magnesium–nickel (MgxNi) alloy films as both a variable emissivity material and top conductive electrode simplifies the device structure and ensures that large changes in emissivity can be achieved. The constructed sandwich‐structured electrochromic devices also have polyethyleneimine (PEI) as a middle proton‐conducting electrolyte layer and hydrogen tungsten bronze (HxWO3)/indium tin oxide (ITO) as a bottom ion‐storage layer. Upon application of a voltage of ±2.6 V, the emissivity of the MgxNi/Pd/PEI/HxWO3/ITO device can be reversibly regulated, with emissivity changes of 0.48 and 0.43 in the 3–5 and 7.5–14 µm atmospheric windows, respectively. Under open‐circuit conditions, the high‐emissivity state of the device can be stably maintained for 3 h. The emissivity change is affected by the composition and thickness of the MgxNi film and the device failure mechanism involves the breakage and oxidation of this film after cycling. Corresponding flexible devices that exhibit electrochromism in the visible region have great potential for adaptive thermal camouflage, smart thermal management, and dynamic information displays.