Magnesium ammonium phosphate nanosheets: Synthesis, characterization, and electrochemical performance for high-capacity supercapacitors

Abstract

Magnesium ammonium phosphate (MAP) nanosheets are emerging as a promising material for next-generation energy storage systems due to their unique physicochemical properties. Here, we report a straightforward and facile chemical synthesis of MAP nanosheets using different molar concentrations of urea. X-ray diffraction analysis confirmed the crystalline structure and formation of the MAP phase while scanning, and transmission electron microscopy revealed triangular nanosheets with a typical thickness of 30–70 nm. Among the synthesized samples, the MAP electrode prepared using M − 2 sample exhibited a high specific capacitance of 330 F g⁻¹ and specific capacity of 198 C g⁻¹ at 5 mV s⁻¹ scan rate. In addition, galvanostatic charge-discharge measurements revealed a specific capacitance of 175 F g⁻¹ and a specific capacity of 105 C g⁻¹ at 1 A g⁻¹ current density. Furthermore, the electrochemical performance was evaluated using a two-electrode system, where the M − 2 sample served as the positive electrode and reduced graphene oxide (rGO) as the negative electrode. The M − 2//rGO assembled supercapacitor device delivered an energy density of 24.25 Wh.kg⁻¹ and a power density of 3600 W kg⁻¹ at a high current density of 4 A g⁻¹, along with superior cyclic stability retaining ∼78 % of its capacity and achieving 99 % coulombic efficiency. The constructed MAP electrode highlights its potential in portable and bendable energy storage devices due to its high capacitive performance for supercapacitors. Furthermore, its high conductivity, large surface area and biocompatibility open opportunities for applications in energy conversion technologies such as fuel cells, electrolyzers for hydrogen production, and biomedical energy devices.