Efficient photothermal conversion in a Ti₃C₂T_x/Bi₂Se₃ hybrid for infrared stealth

Reagents

Titanium aluminum carbide (Ti₃AlC₂, 400 mesh) was purchased from 11 Technology Co. Ltd. Sodium hydroxide (NaOH), ascorbic acid (AA), selenium dioxide (SeO₂), bismuth acetate, cupric acetate and lithium fluoride (LiF) were purchased from Macklin Biochemical Co., Ltd. Hexadecyltrimethylammonium bromide (CTAB) and Hydrochloric acid (HCl) were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemicals were used as received without further purification. Deionized water with a resistivity of about 18.25 MΩ·cm was used as the solvent in all experiments.

Synthesis of Bi₂Se₃ nanoflowers

To synthesize Bi₂Se₃ nanoflowers, Se nanodisks were employed as structural templates. For Se nanodisks, 1 mL of NaOH (0.1 M), 1 mL of CTAB (0.1 M), 1 mL of AA (0.1 M), 0.4 mL of SeO₂ (0.01 M), and 0.1 mL of cupric acetate (0.01 M) were added to 5 mL of deionized water. Then, the mixture solution was put in the vacuum oven at 90 °C for 8 h. The final product was centrifuged at 5,500 rpm for 5 min and washed two times with deionized water to remove the supernatant. Then, 1 mL of NaOH (0.1 M), 1 mL of CTAB (0.1 M), 1 mL of AA (0.1 M), 0.18 mL of SeO₂ (0.01 M), and 0.01 mL of bismuth acetate (0.01 M) were added to 5 mL of Se nanodisks. The mixture solution was subsequently transferred to the vacuum oven at 90 °C for 8 h. The final product was centrifuged and dried at 70 °C for 12 h. To remove the residual Se in Bi₂Se₃, the powder product was annealed at 230 °C for 2 h.

Synthesis of Ti₃C₂T_x and Ti₃C₂T_x/Bi₂Se₃

Ti₃C₂T_x MXene was synthesized by a typical etching method. Briefly, 1 g of LiF was incrementally added to a beaker containing 20 mL of HCl. Then, 1 g of Ti₃AlC₂ was introduced in increments every 5 min under magnetic stirring in an ice-water bath. The mixture was stirred at room temperature for 1 h and transferred to a 35 °C oil bath for 24 h to remove the aluminum layer. Etched MXene was centrifuged at 3,500 rpm and rinsed with deionized water until the pH surpassed 5.5. The final product was obtained after ultrasonication for 2 h under an argon atmosphere and an ice-water bath. To prepare MXene/Bi₂Se₃, MXene (25 μg mL^-1) was mixed with different amounts of Bi₂Se₃ and ultrasonicated for 30 min.

Photothermal conversion test

To evaluate the photothermal conversion of MXene/Bi₂Se₃ hybrids, the mixed suspension (1.4 mL, 25 μg mL^-1) was irradiated with 808 and 980 nm lasers at a power density of 1.0 W/cm². A thermal camera and thermocouples were employed to monitor the temperature variation of the different samples continuously under 25.5 ± 2.5 °C.

Characterizations

The morphology and microstructure were characterized using Scanning Electron Microscopy (ZEISS GeminiSEM 300, Germany) and Transmission Electron Microscopy (FEI Talos F200X G2, America). The materials were further analyzed on the X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha, America). The surface elemental properties of the samples were analyzed using X-ray diffraction (Rigaku SmartLab SE, Japan) with Cu Kα radiation. The energy band structure were tested on Ultraviolet Photoelectron Spectroscopy (Thermo Fisher Scientific ESCALAB Xi, America) and Ultraviolet/visible/near-infrared diffuse reflectance (Shimadzu UV-3600i Plus, Japan). The photoelectrochemical measurements were conducted by an electrochemical workstation (CHI 760E, China) with a three-electrode cell. Absorption spectra and temperature curves were recorded on the spectrophotometer (MAPADA P4, China) and thermocouple (KAIPUSEN YET-610, China). Infrared images were captured on a thermal imaging camera (FLIR A615, America). And the laser power was calibrated with a power meter (THORLABS PM100D, America). The error bars in this work represent the standard deviation calculated using the row statistics analysis function built into Origin 2021 software.

Preparation and characterization

The Bi₂Se₃ nanoflowers were synthesized via a facile hydrothermal method employing preformed Se nanodisks as sacrificial templates, with a detailed process illustrated in Figure 1A. First, the sacrificial templates of Se were synthesized via Cu²⁺-directed growth under alkaline conditions. The SEM image in Supplementary Figure 1 demonstrates its two-dimensional disk-like nanostructure. Subsequent injection of a Bi precursor into the solution initiated epitaxial development of ultrathin Bi₂Se₃ nanosheets uniformly across the Se-disk surfaces. Figure 1B and Supplementary Figure 2 show the SEM images of the finally formed Bi₂Se₃, which possesses a distinct flower-like structure assembled from numerous beautiful ultrathin Bi₂Se₃ nanosheets. Supplementary Figure 3 presents the electron image and energy-dispersive X-ray spectroscopy (EDS) data acquired on the same area imaged in Figure 1B. The EDS mapping exhibits strong Bi and Se signals, confirming the successful synthesis of Bi₂Se₃ nanoflowers. Additionally, the absence of a discernible Cu signal in the elemental mapping indicates the inducing role of Cu²⁺ during synthesis and confirms the reliability of our Cu²⁺-guided growth strategy of Se nanodisks. The trace oxygen in the mapping may be attributed to slight surface oxidation of the sample during the preparation of SEM specimens. As shown in Supplementary Figure 4, monodisperse Ti₃C₂T_x MXene nanosheets were prepared by HF etching in solution. The as-prepared Bi₂Se₃ nanoflowers were subsequently dispersed in the Ti₃C₂T_x MXene solution, and the two components were successfully combined via low-temperature ultrasonication. As depicted in Supplementary Figure 5 and Figure 1C (Ti₃C₂T_x/Bi₂Se₃, SEM), the Bi₂Se₃ nanoflowers have been anchored onto the Ti₃C₂T_x MXene nanosheets. In Figure 1D, the TEM image of MXene/Bi₂Se₃ further clearly resolves the nanoflower architecture of Bi₂Se₃, constructed from numerous interlaced ultrathin nanosheets. And Ti₃C₂T_x MXene flakes are seen to conformally drape over the Bi₂Se₃ surface. In regions where the MXene overlaps with the underlying Bi₂Se₃ sheets, the Ti₃C₂T_x exhibits distinct wrinkles. Furthermore, TEM images recorded at different regions of the Ti₃C₂T_x/Bi₂Se₃ [Supplementary Figure 6 and Figure 1E] clearly resolve distinct boundaries among the Ti₃C₂T_x sheets, Bi₂Se₃ nanoflowers, and substrate. As exhibited in Figure 1F, the high-resolution TEM image recorded from the framed interfacial region reveals a lattice spacing of 0.301 nm, which matches the (015) plane of Bi₂Se₃^[18,19]. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, presented in Figure 1G, shows a feature corroborated with Figure 1D. EDS mappings in Figure 1H-L simultaneously record Bi, Se, Ti, and C elements, furnishing visual proof that all four elements coexist within this hybrid.

Figure 1. (A) Schematic illustration of the synthetic process of MXene/Bi₂Se₃. (B) SEM images of Bi₂Se₃ and (C) MXene/Bi₂Se₃. (D) TEM image, (E and F) HRTEM Images (The insert scalebar is 1 nm), (G) HAADF-STEM image (The insert scalebar is 20 nm), and (H-L) EDS mappings of MXene/Bi₂Se₃.

The XRD measurement was employed to characterize the crystalline structure of the Ti₃C₂T_x/Bi₂Se₃ hybrid. As shown in Figure 2A, diffraction peaks at 5.62°, 16.3°, 27.3°, and 32.92° are indexed to the (002), (004), (006), and (008) planes of Ti₃C₂T_x, respectively^[20,21]. For the Ti₃C₂T_x/Bi₂Se₃ composite, the peaks located at 25.0°, 29.4°, 43.7°, 47.6°, 53.5°, 61.0°, 66.6° and 71.5° can be assigned to (101), (015), (110), (0015), (205), (0210), (1115) and (125) planes of hexagonal Bi₂Se₃ (PDF#33-0214), respectively, which are consistent with previously reported^[22,23]. Notably, phases originating from both MXene and Bi₂Se₃ are clearly observed in the hybrid, indicating the successful formation of the Ti₃C₂T_x/Bi₂Se₃. In addition, XPS analysis was used to study the composition and chemical states of the Ti₃C₂T_x/Bi₂Se₃. In Supplementary Figure 7, the XPS survey manifests the presence of Ti, C, F, Bi, and Se elements in the hybrid. Figure 2B displays the high-resolution XPS spectra of Ti 2p in Ti₃C₂T_x and Ti₃C₂T_x/Bi₂Se₃. For Ti₃C₂T_x, peaks at 454.7 and 460.8 eV are assigned to Ti-C bonds. And peaks around 455.5 and 462.0 eV correspond to Ti²⁺ 2p_3/2 and Ti²⁺ 2p_1/2, while those around 456.6 and 464.5 eV are associated with Ti³⁺ 2p_3/2 and Ti³⁺ 2p_1/2^[24-27]. For Ti₃C₂T_x/Bi₂Se₃, the Ti-C component shifts to 453.9 and 460.1 eV, the Ti²⁺ 2p_3/2 and Ti²⁺ 2p_1/2 peaks move to 454.7 and 461.4 eV, respectively, and the Ti³⁺ 2p_3/2 and Ti³⁺ 2p_1/2 signals appear at 455.7 and 463.9 eV. As shown in Figure 2C, the Bi 4f high-resolution XPS spectra illustrate that the two peaks at higher binding energy correspond to Bi 4f₅/₂, while the three at lower energy are assigned to Bi 4f₇/₂^[28,29]. In Bi₂Se₃, the Bi 4f₅/₂ peaks are located at 163.1 and 164.0 eV, and the peaks of Bi 4f₇/₂ stand at 157.8 and 158.6 eV, respectively. In the Ti₃C₂T_x/Bi₂Se₃ hybrid, these peaks shift to 164.6, 163.5, 159.3, and 158.1 eV, respectively. These results indicate electron gain by Ti₃C₂T_x and loss from Bi₂Se₃, confirming the establishment of a built-in electric field directed from Bi₂Se₃ to Ti₃C₂T_x^[30-32]. Figure 2D presents the high-resolution Se 3d XPS spectra of Bi₂Se₃ and Ti₃C₂T_x/Bi₂Se₃. The peaks located at 53.2 and 54.4 eV are assigned to Se 3d_3/2 and Se 3d_5/2 of Se^2-[33,34], respectively. And Supplementary Figure 8 gives the high-resolution XPS spectra of C 1s in Ti₃C₂T_x and Ti₃C₂T_x/Bi₂Se₃. All the evidence above confirms the successful formation of the Ti₃C₂T_x/Bi₂Se₃ hybrid.

Figure 2. (A) XRD patterns for Bi₂Se₃ and Ti₃C₂T_x/Bi₂Se₃. (B) Ti 2p, (C) Bi 4f, and (D) Se 3d high-resolution XPS spectra for Ti₃C₂T_x/Bi₂Se₃ and components.

Enhanced photothermal conversion performance and mechanism study

Recently, Ti₃C₂T_x MXene has gained widespread recognition as an efficient photothermal material. To harness this optic merit and explore the infrared stealth potential of the hybrid, the photothermal performance of Ti₃C₂T_x/Bi₂Se₃ was systematically evaluated. Broadband light absorption is a prerequisite for efficient photothermal conversion. Therefore, the UV-VIS-NIR absorbance of Ti₃C₂T_x, Bi₂Se₃, and the hybrid is first compared. The result is presented in Figure 3A. Ti₃C₂T_x MXene exhibits a pronounced plasmonic resonance centered at about 768 nm, attributed to its transversal surface plasmon modes. Meanwhile, it has great broadband light absorption across the UV-to-NIR region. For Bi₂Se_3, it displays a continuous, wide-range extinction profile from the UV to the NIR owing to its intrinsically narrow bandgap, exhibiting a broad and smooth curve without distinct peaks. Additionally, for Ti₃C₂T_x/Bi₂Se₃, the spectrum follows the broad contour of Bi₂Se₃ while exceeding the absorbance of either standalone component, indicating additive broadband absorption from the intimate union of Ti₃C₂T_x and Bi₂Se₃.

Figure 3. (A) Extinction spectra of MXene, Bi₂Se₃, and MXene/Bi₂Se₃. (B) Photothermal curves of the solution (25 μg mL^-1) under 808 nm (1.0 W cm^-2) laser irradiation. (The solid line represents data from a single test, while the shaded area indicate the error bands (SD) derived from three replicate tests. (3) of the corresponding sample by row statistics method). (C) Thermal images of DI water, Bi₂Se₃, and MXene/Bi₂Se₃. The heating and cooling curve of Bi₂Se₃ (D) and MXene/Bi₂Se₃ (E). (F) Cyclic test of photothermal curves of MXene/Bi₂Se₃ (1:5).

Based on the absorption characteristics, we further evaluate the photothermal conversion performance of the as-prepared samples. Under irradiation with an 808 nm near-infrared laser, dispersions of Ti₃C₂T_x MXene, Bi₂Se_3, and Ti₃C₂T_x/Bi₂Se₃ are tested under identical conditions (25 µg mL^-1), with deionized water serving as the blank control. The temperature variation of each solution is recorded in real time using a thermocouple coupled with an infrared thermal camera. Figure 3B shows the photothermal curves with error bands of the samples. Benefiting from strong optical absorption and efficient plasmonic heating, the Ti₃C₂T_x sample increases by about 15.18 °C after 7 min of continuous irradiation. Under identical conditions, deionized water exhibits a negligible increase of about 1.77 °C, whereas the Bi₂Se₃ suspension warms by about 6.8 °C, demonstrating its relatively weak photothermal property. For Ti₃C₂T_x/Bi₂Se₃, we further tune the mass ratio of the two constituents (1:1, 1:5, 1:7) and evaluate the photothermal performance of the different hybrids. As a result, the temperature increments reach about 16.34, 20.02, and 20.49 °C at Ti₃C₂T_x/Bi₂Se₃ with a mass ratio of 1:1, 1:5 and 1:7 [Supplementary Figure 9], respectively. Supplementary Figure 10 presents the extinction spectra of the samples, which increase monotonically with Bi₂Se₃ content. This indicates that the complementary absorption of the two constituents, together with their interfacial coupling, may enhance the overall absorption capability of Ti₃C₂T_x/Bi₂Se₃. This may also be one of the reasons for the observed temperature rise. Nevertheless, although the 1:7 ratio exhibits stronger absorption than 1:5, the temperature rises by merely 0.47 °C. In addition, the two are essentially identical for the 10-min infrared thermal stealth application tests because of the overlap around 10 min on the curves. Taking all these factors into account, the hybrid with a mass ratio of Ti₃C₂T_x and Bi₂Se₃ of 1:5 is selected for further experimentation. Its temperature rise is 1.32 times that of Ti₃C₂T_x and 2.94 times that of Bi₂Se₃, respectively, indicative of the excellent synthetic effect of photothermal conversion. Hereafter, all samples denoted as Ti₃C₂T_x/Bi₂Se₃ refer specifically to the hybrid with a 1:5 mass ratio. Figure 3C presents infrared images of DI water, Ti₃C₂T_x MXene, Bi₂Se₃, and Ti₃C₂T_x/Bi₂Se₃. The color-coded temperature contrast provides intuitive visual evidence of the temperature differences among the samples. These results demonstrate the enhanced photothermal performance of Ti₃C₂T_x MXene/Bi₂Se₃. PCE is a key metric for evaluating photothermal conversion capability. To quantify the enhanced performance of Ti₃C₂T_x/Bi₂Se₃, we collect the heating and cooling data of bare Bi₂Se₃ and the Ti₃C₂T_x/Bi₂Se₃ hybrid at room temperature [Supplementary Figure 11] and calculate their respective PCE. Figures 3D and E show that the time constants fitted from the curves are 474.5 s for bare Bi₂Se₃ and 471.56 s for Ti₃C₂T_x/Bi₂Se₃. Based on previous works^[35-37], the corresponding PCEs are calculated to be 31.88% for Bi₂Se₃ and 51.71% for Ti₃C₂T_x/Bi₂Se₃, with the computational details and corresponding parameters [Supplementary Table 1] provided in the Supplementary Material. Furthermore, Supplementary Figures 12 and 13 display the repeated heating-cooling cycles, from which PCEs of 50.55% and 53.84% were determined for Ti₃C₂T_x/Bi₂Se₃, respectively. Therefore, the Ti₃C₂T_x/Bi₂Se₃ in this work can achieve a PCE of approximately 52.03%, with a standard deviation of 1.67%. This enhancement further demonstrates the internal synergistic effects and strong interaction induced by the coupling of two constituents. Notably, the PCE of Ti₃C₂T_x/Bi₂Se₃ surpasses that of several previously reported works [Supplementary Table 2], such as ReS₂/Bi₂Se₃, Bi₄O₅Br₂/Bi₂S₃, m-MXene/nHAp, and PANi/TiO₂/Ti₃C₂T_x^[38-41], showing great promise in photothermal applications. Cyclic photothermal measurements evaluate the photothermal stability of the Ti₃C₂T_x/Bi₂Se₃ hybrid. As depicted in Figure 3F, irradiation with the 808 nm laser for 9 min raises the temperature to 47.14 °C. When the laser is switched off, the dispersion cools gradually to room temperature. Over a five-cycle heating-cooling process, the maximum temperature varies only marginally. Besides, the photothermal performance of Ti₃C₂T_x/Bi₂Se₃ samples prepared in different batches is evaluated in Supplementary Figure 14. As shown, the maximum temperature-rise difference among samples is just 1.2 °C. These results evidence excellent photothermal stability and reproducibility of Ti₃C₂T_x/Bi₂Se₃.

Photothermal conversion performance under 980 nm irradiation is also evaluated. Supplementary Figure 15A displays the temperature-time profiles of H₂O, Ti₃C₂T_x MXene, Bi₂Se_3, and Ti₃C₂T_x/Bi₂Se₃ under a 980 nm laser at 1.0 W cm^-2. After 7 min of irradiation, the temperature of the Ti₃C₂T_x MXene sample increases by 10.74 °C, while that of the Bi₂Se₃ rises by 8.27 °C. In contrast, the Ti₃C₂T_x/Bi₂Se₃ hybrid exhibited a higher temperature rise of 11.16 °C, surpassing both individual components. It can be found that the temperature increase of the Ti₃C₂T_x/Bi₂Se₃ hybrid under 980 nm laser excitation is slightly lower than that under 808 nm. This phenomenon may be attributed to the fact that 980 nm lies farther from the extinction peak of the hybrid, leading to reduced absorption efficiency and diminished photothermal conversion. Supplementary Figure 15B displays the corresponding infrared thermal images of the tested samples, and the temperature distribution shows good consistency with the temperature-time curves. Similarly, the heating and cooling curves of bare Bi₂Se₃ and Ti₃C₂T_x/Bi₂Se₃ hybrid are recorded. As shown in Supplementary Figure 16, the time constants obtained from fitting the cooling curves are 459.5 s for bare Bi₂Se₃ and 456.9 s for Ti₃C₂T_x/Bi₂Se₃ hybrid. In Supplementary Figure 17A, we tested the temperature variation of Ti₃C₂T_x/Bi₂Se₃ under different laser power densities. It indicates that the temperature rise of the hybrid increases progressively with increasing laser power density. Moreover, the hybrid sample exhibits excellent cyclic stability and reproducibility over five laser on-off cycles at 980 nm [Supplementary Figure 17B]. Collectively, these results demonstrate that Ti₃C₂T_x/Bi₂Se₃ exhibits enhanced photothermal conversion performance and excellent photothermal stability at both 808 and 980 nm, underscoring its significant potential for photothermal-related applications and providing a solid foundation for further utilization.

As previously reported, efficient charge separation in hybrids can significantly prolong the lifetime of carriers and thereby enhance photothermal conversion efficiency^[42,43]. Guided by this, we suppose that effective charge transfer between Ti₃C₂T_x and Bi₂Se₃ constitutes one of the key mechanisms underlying the enhanced photothermal performance of the hybrid. A three-electrode system was employed to experimentally verify the anticipated charge transfer. As shown in Supplementary Figure 18A, Ti₃C₂T_x/Bi₂Se₃ exhibits a significantly higher photocurrent density than bare Bi₂Se₃, evidencing efficient charge transfer and an elevated photogenerated-carrier concentration in the hybrid. In Supplementary Figure 18B, the electrochemical impedance spectroscopy (EIS) of Ti₃C₂T_x/Bi₂Se₃ displays the smallest EIS radius, further confirming its superior carrier generation and charge-separation capability. To further illustrate the charge-transfer pathway within the hybrid, the band structures of Ti₃C₂T_x and Bi₂Se₃ were investigated by ultraviolet photoelectron spectroscopy (UPS) and diffuse-reflectance spectroscopy (DRS). According to Figure 4A-C, the energy maximum of the valence band with respect to the Fermi level of Bi₂Se₃ is 0.40 eV. And its band gap, calculated from the Tauc plot, is 0.44 eV. The measured secondary electron cutoff energies are 16.79 eV for Ti₃C₂T_x and 17.15 eV for Bi₂Se₃, yielding work functions of 4.43 and 4.07 eV (vs. vacuum), respectively. Thus, the positions of the conduction band and valence band of Bi₂Se₃ are calculated to be -4.03 and -4.47 eV, with respect to the vacuum level, respectively. Based on the above results, the energy band structures of the Ti₃C₂T_x and Bi₂Se₃ are illustrated in Figure 4D. As it shows, the Fermi level of Ti₃C₂T_x is lower than that of Bi₂Se₃. Therefore, the electrons will flow from Bi₂Se₃ into Ti₃C₂T_x until a common Fermi level is established at equilibrium. Consequently, Bi₂Se₃ becomes electron-deficient and positively charged, inducing upward band bending, whereas Ti₃C₂T_x accumulates excess electrons and acquires a negative charge, leading to downward band bending. This charge redistribution establishes a built-in electric field that points from Bi₂Se₃ to Ti₃C₂T_x, which is fully consistent with the XPS data. Under illumination, the field drives photogenerated electrons in Bi₂Se₃ toward Ti₃C₂T_x and spatially separates the carriers. This suppression of carrier recombination thereby promotes photothermal conversion.

Figure 4. (A) Valence band with respect to the Fermi level of Bi₂Se_3. (B)The secondary electron cutoff of Ti₃C₂T_x and Bi₂Se₃. (C) Tauc plot of Bi₂Se_3. (D)Band structures of Ti₃C₂T_x and Bi₂Se₃.

Active infrared thermal stealth property

Conventional stealth materials minimize the apparent contrast between an object and its background by suppressing the thermal emissivity of the object. Guided by this principle, we consider whether the same contrast can instead be eliminated by actively raising the emissivity of the surrounding environment, allowing the target to conceal in the thermal background. Motivated by this concept, the exceptional photothermal conversion efficiency and robust stability demonstrated by the Ti₃C₂T_x/Bi₂Se₃ hybrid offer an ideal platform for exploring such an inverse infrared stealth strategy. We constructed a simplified infrared-detection scenario [Supplementary Figure 19] to demonstrate the proposed thermal-stealth concept. In the scene, a bear model around the temperature of 30 °C serves as the genuine target on the left, while a decoy object fabricated from the Ti₃C₂T_x/Bi₂Se₃ hybrid is positioned on the right under identical surrounding conditions. Drawing on the preceding photothermal results, the Ti₃C₂T_x/Bi₂Se₃ solution is selected as the test sample, and the 808 nm laser is employed as the excitation source. Besides, a water control is included to highlight the infrared thermal stealth capability enabled by the photothermal conversion of Ti₃C₂T_x/Bi₂Se₃. As illustrated in Figure 5A, in the initial state, the bear target can be clearly identified in both the H₂O and Ti₃C₂T_x/Bi₂Se₃ systems due to the inherent temperature of the bear target is higher than that of the background. However, the weak photothermal conversion capability of H₂O results in negligible temperature changes within the entire testing time. Therefore, the bear target remains distinctly visible in the detection area even after 10 min of irradiation. In contrast, based on the excellent photothermal response of Ti₃C₂T_x/Bi₂Se₃, it efficiently absorbs the incident light energy and converts it into thermal during irradiation. As the irradiation time increases, the temperature gradually rises and eventually becomes the dominant heat source in the detection environment. Under this circumstance, the temperature of the bear target is gradually lower than that of the heat source environment formed by Ti₃C₂T_x/Bi₂Se₃. As observed in Figure 5A, the bear target gradually becomes concealed in the background with the increase in time. The corresponding video is provided in the Supplementary Movie. Supplementary Figure 20 compares the surface temperatures of the different objects in the scene when H₂O or Ti₃C₂T_x/Bi₂Se₃ is employed as the decoy at the indicated measurement times. As shown, the maximum temperature difference among background, real target, and decoy is only 9.5 °C, and the real target remains the warmest spot, making it readily detectable by infrared detectors when H₂O serves as the decoy. In contrast, the Ti₃C₂T_x/Bi₂Se₃ decoy enlarges the temperature span to 35.6 °C and becomes the hottest object in the scene, furnishing a conspicuously elevated thermal background that may mask the genuine target. Figures 5B and C further present the time-dependent temperature curves of the three objects and the corresponding temperature difference recorded during the 10-min test. The temperature-difference comparison in the figure also underscores the strong photothermal-conversion capability of Ti₃C₂T_x/Bi₂Se₃ and its potential for achieving infrared thermal stealth through photothermal heating. This experiment strongly validates the great potential of photothermal materials for infrared thermal stealth via photothermal conversion. It can be noted that this work offers only a proof-of-concept demonstration of infrared thermal stealth enabled by photothermal materials, as prepared Ti₃C₂T_x/Bi₂Se₃. We are confident that further materials design and optimization, or the exploration of alternative material systems, will enable even more effective infrared thermal stealth through photothermal conversion.

Figure 5. (A) Schematic illustration of infrared thermal stealth. (B) Temperature-time curves in the infrared stealth test progress and (C) corresponding temperature difference of three objects.