°C for 2 h under Ar atmosphere and etching with HF followed by the calcination at 400 °C in air for 2 h [831]. The NPOMC delivered the gravimetric capacitance of 355 F g -1 at 0.5 A g -1 in 1 M H2SO4 which is relatively higher than NOMC (288 F g -1 ) and POMC (303 F g -1 )