Bioinspired MXene nacre with mechanical robustness for highly flexible all-solid-state photothermo-supercapacitor

It remains a huge challenge to engineer MXene-based all-solid-state supercapacitors with high energy density, mechanical robustness, and geometrical flexibility to meet the increasing demand for the next generation of wearable and portable electronic devices because of serious restacking in the system and lacking of strong interactions in individual MXene nanosheets. In this work, inspired by mortar and brick structure of nacre, freestanding MXene nacre was developed via layer-by-layer assembly for mechanical robustness and geometrical flexibility, with its greatly improved photothermal conversion ability and the effectively suppressed restacking of MXene nanosheets. Specifically, 1D cellulose nanofibrils and 2D SnS2 were applied as building blocks for assembling structure-layered 3D architecture and effective intercalator for suppressing recalcitrant restacking of nanosheets. Additionally, the in situ grown SnS2 was also functioned as extra H+ transport paths and superior photothermal promotor. Thanks for the 3D hierarchy, the resulted MXene "nacre" showed excellent mechanical strength (78.3 MPa) without sacrificing flexibility, favorable specific capacitance (190F g(-1) in 1 M H2SO4 at scan rate of 10 mV/s), and a high capacitance retention (87.4% after 5000 cycles), which was higher than those in other reports. The nacre-inspired all-solid-state supercapacitor delivered a high energy density of 6.7 mu Wh cm(-2), 91.5% capacitance retention after 4000 cycles and superior cyclability (over 90% capacitance retention after 500 times of folding/unfolding). Benefiting from electrical transport ability of SnS2 under solar irradiation, the flexible MXene supercapacitor also showed outstanding solar-thermal conversion ability, with 60% increase in capacitance under solar intensity of 1 kW/m(2). This work provides a new strategy for the fabrication of mechanically robust multifunctional MXene electrodes of all-solid-state photothermo-supercapacitors for further applications in structural flexible energy storage devices.