Synthesis of porous NiO using NaBH4 dissolved in ethylene glycol as precipitant for high-performance supercapacitor

A facile reflux method has been developed to prepare porous NiO samples using NaBH4-EG and NaOH-EG as alkaline precipitants, respectively. NaBH4-EG is used as alkaline precipitant for the first time. Precipitants influence the morphology and structure of NiO significantly, further affect their specific capacitances as supercapacitor electrodes. Compared with NaOH, NaBH4-EG as alkaline precipitant shows great superiority on morphology control. NiO synthesized by NaBH4-EG presents spherical spongy shape with high specific surface areas, whereas the sample synthesized by NaOH-EG exhibits agglomerated irregular structure. When being applied as supercapacitor electrodes, the former NiO could achieve an extremely high specific capacitance of 930 F g−1 at a current density of 15 A g−1, significantly higher than that of the latter one (510 F g−1). Moreover, the specific capacitance of the former is as high as 1396 F g−1 after 1000-cycle at 4 A g−1, revealing superb electrochemical characteristics. The impedance measurement discloses that the electrode prepared by the former NiO possesses lower charge-transfer resistance and ion-diffusion resistance, demonstrating the superiority of NaBH4-EG as alkaline precipitant. NaBH4-EG is an excellent precipitant for the synthesis of porous NiO as supercapacitor electrodes.