Amorphous Metal Metaphosphate for Oxygen Reduction

Efficient and cost-effective catalysts for oxygen reduction reaction (ORR) are crucial for the commercialization of metal-air batteries. In this study, we utilized theoretical calculations to guide the material synthesis strategy for preparing catalysts. Using density functional theory (DFT) calculations, we systematically explored the ORR performance of metal metaphosphates (A-M(PO₃)₂, B-M(PO₃)₂, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) with both amorphous and crystalline structures. Amorphous A-Mn(PO₃)₂ showed optimal adsorption energy and the lowest ORR overpotential of 0.32 eV. Phytic acid was employed as a phosphorus source, and the chelating structure of phytic acid molecules and metal ions was broken through the “metal ion pre-adsorption and spatial confinement strategy” of carbon materials with electron-rich centers. Following high-temperature calcination, we successfully prepared a series of amorphous metal metaphosphate composite catalysts for the first time. In 0.1 M KOH electrolyte, both amorphous Mn(PO₃)₂-C/C₃N₄/CQDs (carbon quantum dots) and Mn(PO₃)₂-C/C₃N₄/CNTs (carbon nanotubes) exhibited excellent ORR catalytic activity, with half-wave potentials of 0.85 V and 0.80 V, respectively. A linear correlation between theoretical overpotentials and experimental half-wave potentials was discovered through comparison. This work could open a new avenue to the discovery of highly efficient non-precious metal-based catalysts with amorphous structures.