Wet oxidative functionalization of carbon nanotube cloth to boost its performance as a flexible supercapacitor electrode

•CNT cloth affords flexible binder-free electrode with resistivity as low as 9 µΩ m.•Wet oxidative functionalization pushes the cloth capacitance from 48 up to 71 F g−1.•Carboxylic and phenolic surface groups mostly contribute to the pseudocapacitance.•CNT cloth cyclic stability exceeds 98% over 30,000 cycles at 200 mV s−1 scan rate.•Flexible supercapacitor with CNT cloth electrodes shows excellent performance.