Fig. 2: Crystal structures and electronic states of α-NiMoO₄ and P-β-NiMoO₄.

a Schematic of crystal structure evolution during phosphate substitution. b XPS spectra of Ni 2p in P-β-NiMoO₄ and α-NiMoO₄. c Schematic illustration of the generation of active electric states in different phase NiMoO₄.