Searching for superior air-cathodes is a long-term goal for practical applications of Zn-air batteries (ZABs). The sluggish process of oxygen reduction reaction (ORR) in air cathodes can be accelerated by introducing heteroatoms into carbon networks, due, most probably, to the improved electron and spin densities of carbon atoms, thus leading to the urgent demand of carbonaceous electrocatalysts. Here, N, S-codoped porous carbon materials are successfully prepared via the self-activation pyrolysis of garlic stems, and exhibit promising ORR activities and improved ZABs performances. GSC-900 shows onset and half-wave potentials of 0.89 and 0.80 V vs. reversible hydrogen electrode, and efficient 4 electrons pathway, resistance to methanol crossover effect and CO poison, as well as robust durability after 30,000 s tests in alkaline electrolyte solution. GSC-900 as air cathode in a primary ZABs illustrates 1.19 V discharge voltage at 10 mA cm(-2), and power density of 95 mW cm(-2), higher stability than commercial Pt/C. GSC-900 combined with FeCoOx served as bifunctional ORR/OER air-cathode illustrated robust stability in rechargeable ZABs. Turning the biowastes into value-added products not only contributes to the environmental sustainability, but also provides a rational yet low-cost route for the generation of ORR electrocatalysts for metal-air batteries or fuel cells. (C) 2017 Elsevier Ltd. All rights reserved.