“…Atom trapping method is a newly developed strategy to synthesize SAECs. At high temperatures, metal nanoparticles (Pt, Pd, Au, Rh, and Ni nanoparticles) [ 88 , 97 , 98 ], metal bulks (Pt net, Au foil, Pd bulk, Nb bulk, Cu foam, Co foam, and Ni foam) [ 99 – 101 ], metal oxides (Fe 2 O 3 , Co 2 O 3 , Cu 2 O, SnO 2 , and MoO 3 ) [ 87 ], and metal salts (CoCl 2 , H 2 PtCl 6 , H 2 PdCl 4 , HAuCl 4 , and H 2 IrCl 6 ) [ 89 , 102 ] could release metal atom vapor, which could be trapped by various substrates placed in the downstream and form corresponding SAECs. For example, Nb atom vapor released by arc discharge of Nb bulk could be trapped by carbon and formed the single-atom Nb-in-C catalyst [ 99 ].…”