Phase change materials (PCMs) have triggered considerable attention as candidates for solar‐thermal energy conversion. However, their intrinsic low thermal conductivity prevents the rapid spreading ...of heat into the interior of the PCM, causing low efficiencies in energy storage/release. Herein, anisotropic and lightweight high‐quality graphene aerogels are developed by directionally freezing aqueous suspensions of polyamic acid salt and graphene oxide to form vertically aligned monoliths, followed by freeze‐drying, imidization at 300 °C and graphitization at 2800 °C. After impregnating with paraffin wax, the resultant phase change composite (PCC) exhibits a high transversal thermal conductivity of 2.68 W m−1 K−1 and an even higher longitudinal thermal conductivity of 8.87 W m−1 K−1 with an exceptional latent heat retention of 98.7%. When subjected to solar radiation, solar energy is converted to heat at the exposed surface of the PCC. As a result of the PCC's high thermal conductivity in the thickness direction, heat can spread readily into the interior of the PCC enabling a small temperature gradient of <3.0 K cm−1 and a fast charging feature. These results demonstrate the potential for real‐time and fast‐charging solar‐thermal energy conversion using phase change materials with tailored anisotropy in their thermal properties.
Anisotropic and high‐quality graphene aerogels are fabricated by directional‐freezing of polyamic acid salt/graphene oxide slurries, followed by freeze‐drying, imidization, and graphitization. A phase change composite derived from the aerogel exhibits both high longitudinal thermal conductivity of ≈8.87 W m−1 K−1 and excellent latent heat retention of 98.7% with satisfactory stability, and is suitable for real‐time and fast solar‐thermal energy conversion.
2D transition metal carbides and nitrides (MXenes) have gained extensive attention recently due to their versatile surface chemistry, layered structure, and intriguing properties. The assembly of ...MXene sheets into macroscopic architectures is an important approach to harness their extraordinary properties. However, it is difficult to construct a freestanding, mechanically flexible, and 3D framework of MXene sheets owing to their weak intersheet interactions. Herein, an interfacial enhancement strategy to construct multifunctional, superelastic, and lightweight 3D MXene architectures by bridging individual MXene sheets with polyimide macromolecules is developed. The resulting lightweight aerogel exhibits superelasticity with large reversible compressibility, excellent fatigue resistance (1000 cycles at 50% strain), 20% reversible stretchability, and high electrical conductivity of ≈4.0 S m−1. The outstanding mechanical flexibility and electrical conductivity make the aerogel promising for damping, microwave absorption coating, and flexible strain sensor. More interestingly, an exceptional microwave absorption performance with a maximum reflection loss of −45.4 dB at 9.59 GHz and a wide effective absorption bandwidth of 5.1 GHz are achieved.
A 3D, electrically conductive, mechanically strong, and flexible MXene‐based aerogel reinforced with polyimide is fabricated for the first time. The conductive MXene/polyimide aerogel shows superelasticity, excellent resistance to fatigue for 1000 compression cycles under 50% strain, and thermal stability and fire retardancy, demonstrating its potential applications as multifunctional strain sensors and high‐performance microwave absorption coatings.
Although multifunctional, flexible, and wearable textiles with integrated smart electronics have attracted tremendous attention in recent years, it is still an issue to balance new functionalities ...with the inherent performances of the textile substrates. 2D early transition metal carbides/nitrides (MXenes) are considered as ideal nanosheets for fabricating multifunctional and flexible textiles on the basis of their superb intrinsic electrical conductivity, tunable surface chemistry, and layered structure. Herein, highly conductive and hydrophobic textiles with exceptional electromagnetic interference (EMI) shielding efficiency and excellent Joule heating performance are fabricated by depositing in situ polymerized polypyrrole (PPy) modified MXene sheets onto poly(ethylene terephthalate) textiles followed by a silicone coating. The resultant multifunctional textile exhibits high electrical conductivity of ≈1000 S m−1 in conjunction with an exceptional EMI shielding efficiency of ≈90 dB at a thickness of 1.3 mm. The thin silicone coating renders the hydrophilic PPy/MXene‐decorated textile hydrophobic, leading to an excellent water‐resistant feature while retaining a satisfactory air permeability of the textile. Interestingly, the multifunctional textile also exhibits an excellent moderate voltage‐driven Joule heating performance. Thus, the deposition of PPy‐modified MXene followed by silicone coating creates a multifunctional textile that holds great promise for wearable intelligent garments, EMI shielding, and personal heating applications.
An efficient and scalable dip‐coating approach for the fabrication of flexible multifunctional transition metal carbides/nitrides (MXenes)‐derived textiles by decorating polypyrrole‐modified MXene sheets onto polyethylene terephthalate textiles followed by silicone coating is reported. The highly conductive and hydrophobic textiles show exceptional electromagnetic interference shielding efficiency, outstanding water‐resistant feature, and excellent Joule heating performances.
Although flexible and multifunctional textiles are promising for wearable electronics and portable device applications, the main issue is to endow textiles with multifunctionalities while maintaining ...their innate flexible and porous features. Herein, a vacuum‐assisted layer‐by‐layer assembly technique is demonstrated to conformally deposit electrically conductive substances on textiles for developing multifunctional and flexible textiles with superb electromagnetic interference (EMI) shielding performances, superhydrophobicity, and highly sensitive humidity response. The formed leaf‐like nanostructure is composed of silver nanowires (AgNWs) as the highly conductive skeleton (vein) and transition metal carbide/carbonitride (MXene) nanosheets as the lamina. The presence of MXene protects AgNWs from oxidation and enhances the combination of AgNWs with the fabric substrate, and the transformation of its functional groups leads to self‐derived hydrophobicity. The flexible and multifunctional textile exhibits a low sheet resistance of 0.8 Ω sq−1, outstanding EMI shielding efficiency of 54 dB in the X‐band at a small thickness of 120 µm, and highly sensitive humidity responses, while retaining its satisfactory porosity and permeability. The self‐derived hydrophobicity with a large contact angle of >140° is achieved by aging the hydrophilic MXene coated silk. The wearable multifunctional textiles are highly promising for applications in intelligent garments, humidity sensors, actuators, and EMI shielding.
A biomimetic leaf‐like nanostructure composed of a 1D AgNWs skeleton (vein) and 2D MXene as the lamina is fabricated via vacuum‐assisted layer‐by‐layer assembly for electromagnetic interference (EMI) shielding, humidity monitoring, and self‐derived hydrophobicity. The (MA1)10 silk presents an exceptional EMI shielding effectiveness of ≈90 dB at 12.4 GHz at a thickness of 480 µm, and the MXene‐coated textile induces a hydrophilic‐to‐hydrophobic transition, generating a large contact angle of >140°.
Ultrathin, lightweight, and flexible electromagnetic‐interference (EMI) shielding materials are urgently required to manage increasingly serious radiation pollution. 2D transition‐metal carbides ...(MXenes) are considered promising alternatives to graphene for providing excellent EMI‐shielding performance due to their outstanding metallic electrical conductivity. However, the hydrophilicity of MXene films may affect their stability and reliability when applied in moist or wet environments. Herein, for the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine‐induced foaming process. In striking contrast to well‐known hydrophilic MXene materials, the MXene foams surprisingly exhibit hydrophobic surfaces and outstanding water resistance and durability. More interestingly, a much enhanced EMI‐shielding effectiveness of ≈70 dB is achieved for the lightweight MXene foam as compared to its unfoamed film counterpart (53 dB) due to the highly efficient wave attenuation in the favorable porous structure. Therefore, the hydrophobic, flexible, and lightweight MXene foam with an excellent EMI‐shielding performance is highly promising for applications in aerospace and portable and wearable smart electronics.
A hydrophobic, lightweight, and flexible MXene foam is fabricated for the first time by a hydrazine‐induced foaming process. The hydrophobic porous structure affords an extraordinary water tolerance, good durability, and strong absorption capacity. A much enhanced electromagnetic‐interference shielding effectiveness of 70 dB is achieved for the MXene foam as compared to the corresponding unfoamed film, due to the favorable porous structure.
Although many solar‐driven water evaporators are developed for solar steam generation, most solarthermal energy conversion materials cannot be used repeatedly for constructing solarthermal water ...evaporators with variable shapes and patternable surfaces. Herein, reshapable Ti3C2Tx MXene/graphene oxide (GO)/polyaniline (PANI) (MGP) hybrids with variable shapes and patternable surfaces are fabricated by PANI‐assisted assembly of GO and MXene for efficient solar‐driven purifications of both seawater and wastewater. The variable shapes, patternable surfaces, and reusability of the plastic MGP hybrids are attributed to the strong interactions of PANI with both GO and MXene. Benefiting from the excellent solarthermal energy conversion of hydrophilic GO and MXene, the variable shapes and patternable surfaces of the MGP, and the reduced water vaporization enthalpy, the patternable MGP evaporators with flat and concave pyramid surfaces exhibit average water evaporation rates of as high as 2.89 and 3.30 kg m−2 h−1 under 1‐sun irradiation, respectively. When the plastic MGP is molded to a flower‐shaped evaporator, an outstanding evaporation rate of ≈3.94 kg m−2 h−1 with an exceptional evaporation efficiency of ≈135.6% is achieved under 1‐sun irradiation. The reusable MGP evaporators are highly efficient in generating clean water from both seawater and wastewater with satisfactory ion rejection rates of nearly 100%.
Reshapable Ti3C2Tx MXene/graphene oxide (GO)/polyaniline (PANI) (MGP) hybrids with variable shapes and patternable surfaces are fabricated for efficient solar‐driven purifications of both seawater and wastewater by PANI‐assisted assembly of GO and MXene. The patternable MGP evaporators with a concave pyramid surface and a flower‐like shape exhibit outstanding water evaporation rates of 3.30 and 3.94 kg m−2 h−1 under 1‐sun irradiation, respectively.
The development of fully foldable energy storage devices is a major science and engineering challenge, but one that must be overcome if next‐generation foldable or wearable electronic devices are to ...be realized. To overcome this challenge, it is necessary to develop new electrically conductive materials that exhibit superflexibility and can be folded or crumpled without plastic deformation or damage. Herein, a graphene film with engineered microvoids is prepared by reduction (under confinement) of its precursor graphene oxide film. The resultant porous graphene film can be single folded, double folded, and even crumpled, but springs back to its original shape without yielding or plastic deformation akin to an elastomeric scaffold after the applied stress is removed. Even after thermal annealing at ≈1300 °C, the folding performance of the porous graphene film is not compromised and the thermally annealed film exhibits complete foldability even in liquid nitrogen. A solid‐state foldable supercapacitor is demonstrated with the porous graphene film as the device electrode. The capacitance performance is nearly identical after 2000 cycles of single‐folding followed by another 2000 cycles of double folding.
A graphene film with microvoids is prepared by reduction of graphene oxide film. It can be double folded and even crumpled, but springs back to its original shape without yielding or plastic deformation akin to an elastomeric scaffold. When used as the electrodes of a solid‐state supercapacitor, the capacitance performance is nearly identical after 2000 cycles of single folding, followed by another 2000 cycles of double folding.
Light‐weight and high‐performance electromagnetic interference (EMI)‐shielding epoxy nanocomposites are prepared by an infiltration method using a 3D carbon nanotube (CNT) sponge as the 3D ...reinforcement and conducting framework. The preformed, highly porous, and electrically conducting framework acts as a highway for electron transport and can resist a high external loading to protect the epoxy nanocomposite. Consequently, a remarkable conductivity of 148 S m−1 and an outstanding EMI shielding effectiveness of around 33 dB in the X‐band are achieved for the epoxy nanocomposite with 0.66 wt% of CNT sponge, which is higher than that achieved for epoxy nanocomposites with 20 wt% of conventional CNTs. More importantly, the CNT sponge provides a dual advantage over conventional CNTs in its prominent reinforcement and toughening of the epoxy composite. Only 0.66 wt% of CNT sponge significantly increases the flexural and tensile strengths by 102% and 64%, respectively, as compared to those of neat epoxy. Moreover, the nanocomposite shows a 250% increase in tensile toughness and a 97% increase in elongation at break. These results indicate that CNT sponge is an ideal functional component for mechanically strong and high‐performance EMI‐shielding nanocomposites.
High‐performance electromagnetic interference shielding epoxy nanocomposites are prepared using a preformed highly porous and electrically conductive CNT sponge. The CNT sponge acts as the three‐dimensional conducting framework and as effective reinforcement. Only 0.66 wt% of CNT sponge leads to an outstanding EMI shielding effectiveness of around 33 dB in the X‐band, and vast increments in the flexural strength and tensile toughness are achieved.
2D transition metal carbides and nitrides (MXenes), a class of emerging nanomaterials with intriguing properties, have attracted significant attention in recent years. However, owing to the highly ...hydrophilic nature of MXene nanosheets, assembly strategies of MXene at liquid–liquid interfaces have been very limited and challenging. Herein, through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface, we report the formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), which can significantly enhance the interfacial activity of MXene nanosheets. More importantly, this simple assembly strategy opens a new platform for the fabrication of functional MXene assemblies from mesoscale (e.g., structured liquids) to macroscale (e.g., aerogels), that can be used for a range of applications, including nanocomposites, electronic devices, and all‐liquid microfluidic devices.
We're jammin’: The formation, assembly, and jamming of a new type MXene‐based Janus‐like nanoparticle surfactants, termed MXene‐surfactants (MXSs), is reported through the cooperative assembly of MXene and amine‐functionalized polyhedral oligomeric silsesquioxane at the oil–water interface. The MXSs can significantly enhance the interfacial activity of MXene nanosheets.
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