One‐Step Pickering Emulsion Strategy for Flexible Aramid Nanofiber‐Based Composite Phase Change Film With Enhanced Photothermal Conversion and Mechanical Robustness

Shape‐stabilized composite phase change materials are attractive for solar‐thermal energy storage but are often limited by leakage, weak mechanical strength, and insufficient photothermal responsiveness. Herein, we report a one‐step Pickering emulsion strategy to fabricate a flexible aramid nanofiber (ANFs)‐based composite phase change film (APCMF) incorporating 10 wt% CoFe ₂ O ₄ nanoparticles. ANFs simultaneously function as Pickering emulsifiers and structural skeletons, enabling uniform encapsulation of eicosane within a robust aerogel network. The resulting APCMF achieves a high latent heat storage of 143.2 J/g, retaining an impressive 141.3 J/g (98.7% retention) after 200 thermal cycles. Furthermore, its unique mortar–concrete‐like framework ensures remarkable mechanical robustness, exhibiting a tensile strength of 1.22 MPa and sustaining over 1000 bending cycles without structural failure. Moreover, the incorporation of CoFe ₂ O ₄ endows the film with strong solar absorption and efficient photothermal response, allowing a rapid temperature rise to 75.6°C under simulated sunlight, far surpassing pure eicosane. This scalable methodology integrates leakage resistance, thermal reliability, mechanical flexibility, and solar‐thermal conversion into a single material platform, demonstrating significant potential for flexible thermal management, wearable electronics, and solar energy harvesting applications.