Effect of thermal annealing on electrochemical and morphological properties of printed NiO electrodes for flexible asymmetric micro-supercapacitor applications

We report the effects of thermal annealing on screen-printed NiO electrodes for asymmetric battery-type supercapacitors on flexible substrates. Ni(OH)2 was synthesized and annealed at 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C and 800 degrees C to obtain six morphologically diverse NiO samples. FE-SEM, XRD, BET, and four-probe measurements were used to investigate their morphology, crystallinity, surface area, and conductivity, respec-tively. Six symmetric supercapacitors were screen-printed on a PET substrate with 1 M H2SO4 electrolyte to probe their electrochemical properties. NiO annealed at 400 degrees C (NiO-400) demonstrated the highest areal capacitance of 19.54 mF/cm2 coupled with reduced charge-transfer resistance, consistent with the highly porous yet continuous structure observed via FE-SEM and BET surface analysis. With this, an inter-digital asymmetric supercapacitor with NiO-400 cathode and graphene anode was fabricated to demonstrate high areal capacitance of 26.42 mF/cm2, a wide potential window of 1.5 V (at 97.3% coulombic efficiency) and excellent flexibility with 96.4% retention (180 degrees) after 1000 cycles.

Automated summary

The effects of thermal annealing on screen-printed NiO electrodes for asymmetric battery-type supercapacitors on flexible substrates were investigated. Six morphologically diverse NiO samples were obtained by synthesizing and annealing Ni(OH)2 at different temperatures. The NiO annealed at 400 degrees C demonstrated the highest areal capacitance of 19.54 mF/cm2 and reduced charge-transfer resistance, which was consistent with its highly porous yet continuous structure. An inter-digital asymmetric supercapacitor with NiO-400 cathode and graphene anode exhibited high areal capacitance of 26.42 mF/cm2, a wide potential window of 1.5 V (at 97.3% coulombic efficiency), and excellent flexibility with 96.4% retention (180 degrees) after 1000 cycles.