Ultrathick Interlayer Coupled Reduced Graphene Oxide Films for Multidirectional Heat Transport and Electrothermal Energy Conversion

ABSTRACT Efficient thermal management remains a key challenge for high‐power electronics due to the limited availability of materials capable of withstanding extreme heat fluxes (>1000 W·cm −2 ). Although individual graphene sheets exhibit exceptional intrinsic thermal conductivities, stacked graphene films suffer from severe thermal anisotropy and poor through‐plane heat transport because of the weak van der Waals interactions. Here, we report a scalable strategy to construct interlayer‐coupled reduced graphene oxide (rGO) films with covalent carbon bonding across stacking layers. Partially oxidized GO films with controlled hydroxyl densities are first connected by aryl ether bridges via nucleophilic aromatic substitution, which transform into robust carbon linkages upon graphitization. A representative 200 µm‐thick film simultaneously exhibits high in‐plane and through‐plane thermal conductivities of 1465 ± 63 and 14.0 ± 1.2 W·m −1 ·K −1 , respectively. Comparable performance is retained at a thickness of 300 µm and temperatures up to 250°C. Under an extreme heat flux of 1200 W·cm −2 , the film lowers its temperature by 110°C within 20 s and shows excellent cycling stability. The high thermal and electrical conductivities also enable fast, uniform, and durable electrothermal heating. This work provides a practical route to overcoming the intrinsic anisotropy of graphene assemblies for advanced thermal management applications.