Magnetically Aligned Ultrafine Cobalt Embedded 3D Porous Carbon Metamaterial by One‐Step Ultrafast Laser Direct Writing

Spatial manipulation of nanoparticles (NPs) in a controlled manner is critical for the fabrication of 3D hybrid materials with unique functions. However, traditional fabrication methods such as electron‐beam lithography and stereolithography are usually costly and time‐consuming, precluding their production on a large scale. Herein, for the first time the ultrafast laser direct writing is combined with external magnetic field (MF) to massively produce graphene‐coated ultrafine cobalt nanoparticles supported on 3D porous carbon using metal–organic framework crystals as precursors (5 × 5 cm(2) with 10 s). The MF‐confined picosecond laser scribing not only reduces the metal ions rapidly but also aligns the NPs in ultrafine and evenly distributed order (from 7.82 ± 2.37 to 3.80 ± 0.84 nm). ≈400% increment of N‐Q species within N compositionis also found as the result of the special MF‐induced laser plasma plume. (). The importance of MF is further exmined by electrochemical water‐splitting tests. Significant overpotential improvements of 90 and 150 mV for oxygen evolution reaction and hydrogen evolution reaction are observed, respectively, owing to the MF‐induced alignment of the NPs and controlled elemental compositions. This work provides a general bottom‐up approach for the synthesis of metamaterials with high outputs yet a simple setup.