▎ 摘　　要

Herein, we develop a transient heating-quenching strategy triggered by Joule heating for the synthesis of single-atom cobalt- and nitrogen-doped graphene materials with three-dimensional porous monolithic architecture (denoted as CoNG-JH). The ultrafast Joule heating procedure simultaneously enables the reduction of graphene oxide and the incorporation of metal and nitrogen atoms into the graphene matrix within 2-second period. Meanwhile, the transient quenching avoids the extended heating-induced atom aggregation, ensuring the rapid and stable dispersion of atomic-scale CoNx active sites in graphene. Additionally, the interconnected macropores and nanopores formed by the self-assembly of graphene sheets facilitate the unimpeded ion and gas transport during the catalytic process. When used as an electrode for the hydrogen evolution reaction (HER), the fabricated freestanding CoNG-JH exhibits high catalytic activity and durability with a low overpotential of 106 mV at 10 mA.cm(-2) and a small Tafel slope of 66 mV.dec(-1) in 0.5 M H2SO4 electrolyte. The presented synthesis and design strategy open up a rapid and facile route for the manufacturing of single atom catalysts.