In our present work

a typical biomass

maize straw was used as precursor to prepare porous biochar under high temperature followed with etching by KOH solution. The prepared biochar was characterized by powder X-ray diffraction (XRD)

scanning electron microscopy (SEM)

Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy (Raman). The specific surface area of as-prepared biochar was calculated by the Brunauer-Emmett-Teller (BET) method. Under the optimal conditions

the specific surface area can reach 1228 m2·g-1. Then the as-prepared biochar was employed as electrode materials to fabricate the flexible supercapacitor cooperating with the H2SO4/PVA gel as electrolyte. The electrochemical capacitance properties of the obtained supercapacitors were tested by cyclic voltammetry (CV) constant current charge-discharge (CD) and AC impedance spectroscopy (EIS) measurements in a two-electrode system. The results showed that the specific capacity reaches 125 F·g-1 when the current density is 1.0 A·g-1. Noteworthily

the fabricated supercapacitor demonstrates the perfectly flexibility and stability that the capacitance retention kept at 93.5% under different bending angles (from 0° to 180°) at a constant current density of 1.0 A·g-1. Furthermore

the flexible supercapacitor also exhibits a satisfied long-term stability performance of 95.6% capacitance retention and 94.9% coulombic efficiency under 180° bending angle through 500 cycles. These very attractive mechanical properties and electrochemical performances enable this flexible supercapacitor to present a great potential for wearable devices as energy storage equipment and open up new avenues to high-value materials from waste maize straw.