Supercritical CO₂‐Synthesis of Amorphous Nickel Oxalate Dihydrate for both Enhanced Catalytic Oxygen Evolution and Urea Oxidation Performance

Abstract Amorphous nanomaterials exhibit significant potential in electrocatalysis, photothermal conversion, and device applications owing to their abundant dangling bonds, unsaturated sites, and isotropy. However, current research still faces challenges such as complex synthesis methods, poor controllability of amorphization, and structural stability. In this work, amorphous transition metal oxalates nickel oxalate dihydrate (NiC₂O₄·2H₂O) nanoparticles are synthesized via a one‐pot method with the assistance of supercritical carbon dioxide (SC CO₂). Notably, for the first time, it is found that the sample prepared at 20 MPa (SC‐20) not only demonstrates exceptional oxygen evolution reaction catalytic activity under alkaline conditions, achieving an overpotential of only 299 mV at a current density of 20 mA·cm⁻², but also exhibits superior urea oxidation reaction performance, achieving a low potential of 1.346 V at 10 mA cm⁻². The outstanding catalytic performance in two typical catalysis reactions originates from the typical amorphous structure led by SC CO₂, which facilitates the formation and stabilization of Ni³⁺ active sites coupled with accelerated Ni²⁺ oxidation kinetics. Therefore this work not only expands the application of SC CO₂ in the synthesis of amorphous materials but also provides novel insights for designing high‐performance amorphous catalytic materials, precisely realizing “killing two birds with one stone.”