Synthesis of amorphous metal oxides via a crystalline to amorphous phase transition strategy

Amorphous metal oxide (AMO) nanomaterials are attractive because of their unique short-range order structure, but controllable synthesis is still challenging. Here we report a Li+-assisted liquid-phase reduction method, which converts a series of crystalline metal oxides into amorphous structures (RuOx, PtOx, CuOx, NiOx, PdOx, MnOx and NiCoOx). Taking RuO2 as an example, in situ Raman and X-ray absorption spectroscopy indicate that the reduction of Ru–O coordination number and distortion of the medium-range structure of Ru–Ru during the amorphization process are caused by naphthalene radical anions and lithium ions. Theoretical calculations indicate that Li⁺ insertion in RuOx strengthens its electrostatic interaction with the naphthalene radical anion, accelerating the stripping of oxygen from Li⁺-inserted RuOx. The introduction of positive charge by Li⁺ insertion can disrupt the internal charge balance of crystal ruthenium oxide, and therefore reduce the formation energy of intermediates for producing amorphous RuOx. This strategy paves a way for achieving the controllable synthesis of AMOs. A Li⁺-assisted liquid-phase reduction method is reported, which converts crystalline metal oxides into amorphous metal oxides. The electrostatic interaction between the naphthalene radical anions and Li⁺-inserted metal oxides is found to promote the amorphization process.