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.

Although graphene-based thermal interface materials (TIMs) have great potentials in removing excess heat generated during highly efficient running of electronic devices, their practical applications are usually limited by their unsatisfactory thermal conductions, which are mainly caused by unsatisfactory dispersion and distribution, low loading, and low quality of graphene sheets, as well as the thermal interfacial resistance between graphene sheets and polymer matrix. Herein, we develop vertically aligned graphene hybrid foams (GHFs) with high densities by hydrothermal reduction of graphene oxide in the presence of high-quality graphene nanoplatelets (GNPs) followed by air-drying. The reduced graphene oxide sheets play an important role in constructing a vertically aligned interconnection network for accommodating GNPs during the hydrothermal reduction process, while the incorporated GNPs not only make the thermal conductance network denser but also prevent excessive shrinkage of the foams during air-drying. More critically, graphitization of GHF at 2800 °C removes the residual oxygen-containing groups and heals the defects of their reduced graphene oxide component, leading to high-quality graphene foams. The resultant vertically aligned high-quality graphene porous architecture with high density as an ideal thermal conductance network of TIMs is highly efficient in improving the thermal conductivity of its epoxy composite, which exhibits an ultrahigh through-plane thermal conductivity of 35.5 W m K at a graphene loading of 19.0 vol %. The excellent thermally conductive performance makes the annealed GHF/epoxy composites suitable for the thermal management.

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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.