Boosting Thermal Generation in Cation-Exchanged Transparent MXene Composite Films with Hierarchical Wrinkled Structure.

Efficient thermal generation from solar/electric energy in transparent films remains challenging due to the limited toolbox of high-performance thermal generation materials and methods for microstructure engineering. Here, we proposed a two-step strategy to introduce hierarchical wrinkles to the MXene composite films with high transparency, leading to upgraded photo/electrothermal conversion efficiency. Specifically, the thin film contains protic acid-treated MXene layers assembled with Ag nanowires (H-MXene/Ag NWs). The hydrogen-bonding interaction between MXene and Ag NWs in a MXene-based thin film forms the first-level wrinkles, while the cation-exchanged method is then developed to enhance conductivity and form the second-level wrinkles. The H-MXene/Ag NWs composite transparent film is observed to achieve a surface temperature rise of 40 °C relative to an ambient environment under 1.0 sun illumination and 70 °C at 1 V voltage in the dark, along with notable photo/electrothermal production stability under ambient conditions. Moreover, experimental and theoretical results show that the improved heat production capability is mainly due to low reflectivity led by the wrinkles and high conductivity led by the cation-exchange process. On the basis of the excellent photothermal generation capability of the H-MXene/Ag NWs composite transparent film, we applied it to biomimetic soft robots and flexible wearable devices. This work paves a novel strategy for the generation of thermal production devices that achieve high-performance photo/electroconversion.