Fig. 1: Preparation scheme and microstructure of nanoporous FeCo/CeO_2−xN_x electrodes.

a Schematic diagram to illustrate fabrication procedure of lamellar nanoporous (NP) FeCo/CeO_2−xN_x composite electrode, during which precursor Fe₁₅Co₅Ce₅Al₇₅ eutectic alloy composed of lamella-nanostructured Al₁₁Ce₃ and Al₁₃(FeCo)₄ intermetallic compounds are prepared by solidification eutectic reaction and then chemically dealloyed in N₂-purged KOH solution to remove less-noble Al, followed by a thermal nitrification process at 600 °C in Ar/NH₃ atmosphere. b Top-view SEM image of NP FeCo/CeO_2−xN_x composite electrode, displaying an architecture composed of periodically alternating hierarchical nanoporous FeCo alloy and nanoporous CeO_2−xN_x lamellas. Scale bar, 200 nm. c XRD patterns of NP FeCo/CeO_2−xN_x composite electrode (pink), as well as its corresponding NP FeCo alloy (blue) and NP CeO_2−xN_x individuals (grey). The line patterns show reference cards 04-0593 and 01-1262 for face-centered cubic CeO₂ and body-centered cubic Fe metal according to JCPDS. d Representative HRTEM image of heterostructured FeCo/CeO_2−xN_x interface. Scale bar, 1 nm. Inset: SAED patterns of FeCo/CeO_2−xN_x heterostructure. Scale bar, 5 1/nm. e, f FFT patterns of FeCo alloy (e) and CeO_2−xN_x (f) in the selected areas in FeCo/CeO_2−xN_x heterostructure in (d). g Typical SEM image and the corresponding EDS elemental mapping images of NP FeCo/CeO_2−xN_x electrode for Fe, Co, Ce, O, and N elements. Scale bar, 200 nm. h High-resolution XPS spectra of Ce 3d, Co 2p, Fe 2p, O 1 s, and N 1 s on the surface of NP FeCo/CeO_2−xN_x electrode.