Bimetallic Nanoparticles Embedded in P,N,Br-Codoped Carbon Matrices Derived from Heterometallic-Organophosphine Frameworks as Electrode Materials for Asymmetric Supercapacitors

An unprecedented method has been developed to obtain heterometallic-organophosphine frameworks (HMOPFs) through a solvent-free, three-component mechanochemical process. In a ball mill, mixing copper (I) bromide with zinc (II), nickel (II) or copper (II) acetates, in the presence of (PTA-CH₂-C₆H₄-p-COOH) Br (PTA is 1,3,5-triaza-7-phosphaadamantane) as an organic linker, has produced the corresponding HMOPFs based on Cu⁺-Zn²⁺, Cu⁺-Ni²⁺ and Cu⁺-Cu²⁺, respectively. The pyrolysis of HMOPFs resulted in bimetallic nanoparticles of transition metal phosphide and phosphate embedded in multi-P,N,Br-codoped carbon matrices (Cu−M@C). Due to the utilization of an aminophosphine organic linker, this HMOPFs-derived approach typifies an eco-friendly synthesis of carbon confined transition metal phosphides or phosphates. It avoids the common conventional methods that involves phosphorylation using large amounts of additional P sources, which leads to an intensive release of the flammable and poisonous phosphine gas. Also, the presence of Br at the organic linker eliminates the need for using bromine vapours to obtain halogen-doped carbon matrices. The Cu−M@C nanocomposites were tested as negative electrode materials for asymmetric supercapacitors. Electrochemical tests included cyclic voltammetry and galvanostatic charge-discharge experiments, which revealed the Cu−Zn@C electrode with a higher potential window as compared to Cu−Ni@C and Cu−Cu@C electrodes, achieving a rate performance of 60 % and high coulombic efficiency.