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Abstract We demonstrate shear‐printed layered photonic films with vivid structural coloration from bio‐derived cellulose nanocrystals and highly aligned Ti₃C₂T_xMXene nanoflakes. These ultrathin films (700–1500 nm) show high light transmittance above 40% in the visible range. In reflectance mode, however, the films appear vividly colored and iridescent due to the multiple distinct photonic bandgaps in the visible and near‐infrared ranges, which are rarely observed in CNC composites. The structural coloration is controlled by the stacking of MXene nanoscale‐thin layers separated by the thicker cellulose nanocrystals matrix, as confirmed by photonic simulations. The unique combination of distinctly different optical appearances in transmittance and reflectance modes occurs in films printed with just a few layers. This is because of the molecularly smooth interfaces and the high refractive contrast between bio‐based and inorganic phases, which result in a concurrence of constructive and destructive interference. These lamellar biophotonic films open the possibilities for advanced radiative cooling, camouflaging, multifunctional capacitors, and optical filtration applications, while the cellulose nanocrystals matrix strengthens their flexibility, robustness, and facilitates sustainability. 

Stacking atomically thin two-dimensional (2D) nanosheet materials leads to unique synergy in their inherent properties due to an intimate combination and matching that is not possible via separate individual components and phases. However, traditional synthesis and assembly methods result in poor architectural control and restricted surface chemistry, thereby limiting their prospective potentials. This brief overview provides consideration of different synthesis and assembly methods for fabrication of diverse novel heterostructures. The advantages and challenges of existing methods are discussed. Finally, future perspectives regarding crafting of heterostructures with highly controllable architectures and interfacial/surface chemistry, and advanced characterization methods are highlighted. 

Abstract Shape‐persistent, conductive ionogels where both mechanical strength and ionic conductivity are enhanced are developed using multiphase materials composed of cellulose nanocrystals and hyperbranched polymeric ionic liquids (PILs) as a mechanically strong supporting network matrix for ionic liquids with an interrupted ion‐conducting pathway. The integration of needlelike nanocrystals and PIL promotes the formation of multiple hydrogen bonding and electrostatic ionic interaction capacitance, resulting in the formation of interconnected networks capable of confining a high amount of ionic liquid (≈95 wt%) without losing its self‐sustained shape. The resulting nanoporous and robust ionogels possess outstanding mechanical strength with a high compressive elastic modulus (≈5.6 MPa), comparable to that of tough, rubbery materials. Surprisingly, these rigid materials preserve the high ionic conductivity of original ionic liquids (≈7.8 mS cm⁻¹), which are distributed within and supported by the nanocrystal network‐like rigid frame. On the one hand, such stable materials possess superior ionic conductivities in comparison to traditional solid electrolytes; on the other hand, the high compression resistance and shape‐persistence allow for easy handling in comparison to traditional fluidic electrolytes. The synergistic enhancement in ion transport and solid‐like mechanical properties afforded by these ionogel materials make them intriguing candidates for sustainable electrodeless energy storage and harvesting matrices.