Fig. 1: Synthesis route and theory prediction.

a Schematic illustration of the fabrication of HEOs hollow nanocube. b The pKsp and ionic radius of different metal ions. c A periodic table of elements highlighting those that can form hollow nanocube HEOs in this study. d, e Total and partial density of states for NiCoFeCdCr-O and NiCoFe-O. f The d-band centers of NiCoFeCdCr-O (blue), NiCoFeCr-O (pink), NiCoFeCd-O (yellow), and NiCoFe-O (purple).