Dual-ligand modulation approach for improving supercapacitive performance of hierarchical zinc–nickel–iron phosphide nanosheet-based electrode

Mixed nanostructured transition metal-based complex materials with hierarchical and porous architectures, built from interconnected nano-building blocks, are considered as high-performance positive electrode materials in supercapacitors (SCs). Herein, zinc–nickel–iron phosphide (ZnNiFe–P) and Zn–Ni–Fe–hydroxide precursors (ZnNiFe–OH) were combined in a 3D hierarchical and porous structure (ZnNiFe–(P/OH)) to improve their durability and electrochemical activity by incorporating a dual-ligand synergistic modulation strategy. The 3D ZnNiFe–(P/OH) architectures, comprising perfectly aligned nanosheet arrays (NSA), were successfully grown on Ni foam using a facile hydrothermal process followed by partial phosphorization. The dual-ligand ZnNiFe–(P/OH) electrode exhibited excellent specific capacitance/areal capacitance (1708 F g⁻¹/5.64 F cm⁻² for 1 A g⁻¹), high rate performance (62% upto 15 A g⁻¹) and good cycle life. Moreover, the ZnNiFe–(P/OH) NSA positive electrode was coupled with an activated carbon negative electrode to design an asymmetric supercapacitor device. The device delivered an excellent capacitance of ∼187 F g⁻¹ at 0.8 A g⁻¹, a superior energy density of ∼58.4 W h kg⁻¹ at 600 W kg⁻¹, and an excellent power density of 11250 W kg⁻¹ at 34.4 W h kg⁻¹ while maintaining good cycling performance (88% after 5000 cycles).