ZIF-67 derived porous core-shell nanocomposites for high-efficiency electromagnetic absorption

•A facile method to prepare Co@CNs with core-shell porous structure by heat treatment of Z@P nanocomposites.•The RLmin of Co@CN-60 is −59.08 dB at 17.66 GHz with a thickness of only 1.7 mm.•The effective absorption bandwidth is broadened ranging from 15.19 to 9.41 GHz (5.78 GHz) when the thickness is 2.3 mm.•The porous core-shell structure of Co@CN-60 not only consume the EMW, but also improve the impedance matching.