Graphene has shown great potential in microwave absorption (MA) owing to its high surface area, low density, tunable electrical conductivity and good chemical stability. To fully realize grapheneʼs MA ability, the microstructure of graphene should be carefully addressed. Here we prepared graphene microflowers (Gmfs) with highly porous structure for high-performance MA filler material. The efficient absorption bandwidth (reflection loss ≤ −10 dB) reaches 5.59 GHz and the minimum reflection loss is up to −42.9 dB, showing significant increment compared with stacked graphene. Such performance is higher than most graphene-based materials in the literature. Besides, the low filling content (10 wt%) and low density (40–50 mg cm−3) are beneficial for the practical applications. Without compounding with magnetic materials or conductive polymers, Gmfs show outstanding MA performance with the aid of rational microstructure design. Furthermore, Gmfs exhibit advantages in facile processibility and large-scale production compared with other porous graphene materials including aerogels and foams. Electronic supplementary materialThe online version of this article (10.1007/s40820-017-0179-8) contains supplementary material, which is available to authorized users.

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As promising carbonaceous films, graphene films (GF) have exhibited many remarkable mechanical and electrical/thermal properties of great potential for wide functional applications. However, the electrical conductivity of GF still needs to be improved and the limitation lies in the low carrier density of pure graphene. Here, we presented a post-doping method for large-area potassium doped graphene films (GF-K) and promoted the electrical conductivity of GF approaching benchmark metals. The macroscopic-assembled GF-K shows a similar color to graphite intercalation compounds. The potassium doping increased the carrier density of the GF without undermining the electronic quality of the graphene unit. The doping concentration was optimized to prepare stage-2 GF-K (CK) with the highest electrical conductivity (1.49 × 10 S m), holding merits of low density (1.63 g cm), and high flexibility. Doped GF with better specific electrical conductivity than copper showed outstanding electromagnetic interference shielding performance. Shielding effectiveness (SE) increased from 70-85 dB for graphene film (GF) to over 130 dB for GF-K only at 31 μm thickness, which is among the best SEs in previous reports. The combination of high specific conductivity, mechanical flexibility, high EMI SE, light weight, and facile productivity enables GF-K to be promising in many high-end EMI applications such as aerospace and wearable devices.