Selective phosphidation of NiGa-Layered double hydroxide for hybrid supercapacitors

Layered double hydroxides (LDHs) materials are ideal electrode materials for supercapacitors (SCs) due to their high capacitance, large surface area and fast redox reaction. However, the limited reaction site of LDHs is one of the main obstacles to increasing the capacitance of SCs. Here, NiGa-LDH grown on nickel foam (NF) by one-step hydrothermal method is derived into Ni2P/NiGa2O4/NiGa-LDH/NF by partial phosphating method induced by NaH2PO2. Ni0.5Ga0.5-LDH/NF has good electrochemical performance, and the capacitance can reach 295 mAh g-1 (2124F g-1) when the current density is 1 A g-1. Significantly, Ni2P/NiGa2O4/NiGa-LDH/NF well preserves the layered structure of LDHs, inherits the low transfer impedance of interlayer ions, and can greatly reduce the thickness of the nanosheets, exposing more active sites and speeding up the electron transfer speed. According to the first principle calculation, Ni2P and NiGa2O4 formed by phosphating helps to increase the free electron ratio in Ni2P/NiGa2O4/NiGa-LDH/NF, thus improving the charge transfer behavior in electrochemical reactions. The material can provide an ultra-high electrochemical capacity of 454.7 mAh g-1 (3274F g-1) at 1 A g-1. In addition, a hybrid supercapacitors (HSCs) is prepared by coupling the Co3O4-C as negative electrode with the high capacitance Ni2P/NiGa2O4/NiGa-LDH/NF as positive electrode. Ni2P/NiGa2O4/NiGa-LDH/NF // Co3O4-C HSCs provides the energy density of 72 Wh kg-1 at the power density of 800 W kg-1 with excellent long-term stability up to 8000 cycles, and is expected to be used in next-generation energy storage systems.

Automated summary

By inducing partial phosphating on NiGa-LDH, the derived Ni2P/NiGa2O4/NiGa-LDH structure effectively improves the capacitance and charge/discharge speed of supercapacitors, while preserving the layered structure of LDHs and reducing the charge transfer impedance. Additionally, the hybrid supercapacitor (HSCs) composed of Co3O4-C negative electrode and Ni2P/NiGa2O4/NiGa-LDH positive electrode demonstrates excellent energy density and long-term stability under high power density.