Conversion of maize straw into nitrogen-doped porous graphitized carbon with ultra-high surface area as excellent oxygen reduction electrocatalyst for flexible zinc–air batteries

Rational design and preparation of waste biomass derived carbon as air electrode catalysts are pivotal for large-scale sustainable development of Zn–air battery, simultaneously promoting waste resource reuse. Herein, a three-dimensional nitrogen-doped porous graphitized carbon (MS-NPC) is designed by employing maize straw as carbon precursors. The N-doping can cause increased active sites for oxygen reduction reaction (ORR), and the FeCl3 activated porous graphitized structure provides an efficient O2 and electrolyte pathway toward easily access to active sites. The resultant N-doped porous graphitized maize straw carbon (MS-NPC) surprisingly exhibits high specific surface area (1483 m2 g−1), high nitrogen content (4.70%), a rather positive onset potential (0.985 V vs. RHE) and large limiting current density (5.8 mA cm−2), which is even better than most reported leading results based on biomass-derived carbon. Density-functional-theory computations confirm the synergetic effect between N-doping and FeCl3 activated porous graphitized structure are promising to accelerate ORR process which is the essential reason for high ORR catalytic performance of MS-NPC. Furthermore, a primary Zn–air battery (ZAB) designed with MS-NPC electrode displays a maximum power density (127.9 mW cm−2), super specific-discharge-capacity (794 mAh gZn−1 at 300 mA cm−2), longtime stability, ZnO immunity and flexible properties. Practical testing verifies that the home-made ZAB can easily power LEDs and electric fans, thereby presenting a promising strategy for the development of economical and highly active carbon as excellent ORR electrocatalyst from waste biomass.