Cobalt phosphate nanorod bundles for efficient supercapacitor and oxygen evolution reaction applications and their temperature dependence

Abstract

Developing highly stable, low-cost, and efficient electrode materials for supercapacitor and oxygen evolution reactions is a challenging issue in energy storage and generation technology to meet the demand for sustainable and clean energy. Herein, cobalt phosphates in comparison with cobalt oxides were synthesized using a successive ionic layer adsorption and reaction (SILAR) method on a nickel foam substrate with different crystallization temperatures, and their supercapacitor and oxygen evolution reaction performances were studied. The nanorod bundles of cobalt phosphate electrodes prepared at 150 °C delivered an excellent specific charge storage capacity of 1512 F g⁻¹ (681 C g⁻¹) at a current density of 5 mA cm⁻², which is higher than that of cobalt oxide (1103.9 F g⁻¹ (496 C g⁻¹)). They are highly stable for more than 2000 charge–discharge cycles with a coulombic efficiency of 93%. Furthermore, the same electrodes exhibited enhanced electrocatalytic behaviour for the oxygen evolution reaction (OER) with an overpotential of 359 mV at a current density of 30 mA cm⁻², lowest Tafel slope of 60 mV dec⁻¹ and stability of 20 hours. Enhanced reaction kinetics are attributed to the high electrochemical surface area with a C_dl of 594 μF and improved electronic conductivity. The above results indicated that cobalt phosphate is one of the most efficient electrode materials for the OER and supercapacitors.