Self-Supported, Sulfate-Functionalized Nickel Hydroxide Nanoplates with Enhanced Wettability and Conductivity for Use...

Nickel hydroxide is promising for use in supercapacitor applications because of its low cost and tunable electrochemical properties, but its performance is usually restricted by insufficient conductivity and surface reactivity. In this work, sulfate-functionalized Ni(OH)₂ (SNO) nanoplates were grown in situ on nickel foam (NF) by a green and facile one-step hydrothermal treatment of NF without the need for an external Ni source or surfactant addition. The resulting material showed a 9.3 times higher areal capacity and 1.8 times higher rate capability than the sulfate-free control and retained 81.3 % capacity after 5000 cycles. If used as the positive electrode in a hybrid supercapacitor, the SNO/NF//activated carbon system achieved >95 % Coulombic efficiency, a maximum energy density of 3.59 Wh m^-2 , and a maximum power density of 44.63 Wm^-2 , which surpass those achievable by most known Ni-based supercapacitors. Detailed material characterization and DFT calculations revealed that the introduction of sulfate expanded the layer spacing of Ni(OH)₂ and improved the electrical conductivity and wettability to favor more efficient electrolyte diffusion, charge transfer, and reactant adsorption. The high loading of reactive components and inherited porous structure also contributed to the superior capacitive performance of the SNO/NF electrodes. Therefore, SNO/NF holds great potential for commercialized supercapacitor applications.