Tuning Electrocatalytic and Charge Storage Properties of NiO Via Fluorine Doping and Thermal Engineering

Fluorine-doped nickel oxides (NiO) samples were synthesized with varying fluorine concentrations and calcinated at different temperatures to investigate their electrocatalytic and energy storage performance. Among the prepared samples, the electrode incorporating 0.02 M NH₄F and calcinated at 500°C (NF52) exhibited superior electrocatalytic activity and charge storage capability. For instance, the NF52 demonstrated excellent oxygen evolution reaction (OER) performance, delivering a low overpotential of 289 mV at the current density of 10 mA cm^-2 and outstanding operational stability for 150 h. A 1.6 V hybrid supercapacitor was further assembled using activated carbon (AC) as the negative electrode and NF50 or NF52 as the positive electrode with a PVA-KOH gel electrolyte. The AC||PVA-KOH||NF52 device delivered a maximum energy density of 24.17 Wh kg^-1 at a power density of 1515.78 W kg^-1. Long-term cycling stability was confirmed over 30,000 galvanostatic charge-discharge (GCD) cycles at a current density of 1 A g^-1, retaining ∼80% of its initial capacitance and maintaining a coulombic efficiency >99%. These results clearly demonstrate that F-doped NiO calcinated at 500°C is a promising bifunctional electrode material for high-performance energy storage and alkaline water electrolysis applications.