Red onions waste-derived biocarbons with remarkably high catalytic activity for the oxygen reduction reaction and high capacitance

Red onion rubbishes, otherwise, potentially abundant wastes, have been identified as source of heteroatoms containing carbon structures. In this work, novel red onion waste-derived self-doped porous biocarbons were successfully obtained by a simple thermochemical process. The effect of increasing temperature during thermal treatment on their structural features, porous complexity, and surface chemistry was analyzed. In addition, these properties were correlated with the catalytic activity for the oxygen reduction reaction (ORR) and specific capacitance of the biocarbons, both evaluated in alkaline media. The most active metal-free biocarbon electrocatalyst, heat treated at 800 °C and labelled as RWB800, showed a remarkable high catalytic activity for the ORR, with an onset potential of 0.97 V vs. RHE, an electron transfer number ( n ) of 3.95 and a percentage of hydrogen peroxide species ( % HO 2 - ) produced between 1.2 and 12%. Moreover, RWB800 demonstrated a high specific capacitance of 309 F g −1 . It can be highlighted that the process to produce the biocarbons shown in this work can be easily scalable, thus offering an alternative for the sustainable use of onion wastes in large-scale production of electrodes for clean energy generation and storage electrochemical devices, such as anion exchange membrane fuel cells and supercapacitors. Graphical abstract