Recycling the biowaste to produce nitrogen and sulfur self-doped porous carbon as an efficient catalyst for oxygen reduction reaction

Abstract

Fossil energy shortage will certainly force/motivate human beings to develop renewable energy technologies to alleviate the burden on already strained energy resources and solve other detrimental socioeconomic issues. Fuel cells and metal–air batteries are presumed upon to be promising for future automotive applications. For this to happen, low-cost, earth-abundant electrocatalysts of the oxygen reduction reaction (ORR) at the cathode are urgently desired to replace the precious noble metal (or noble metal-containing) ones to overcome the inherent sluggish kinetics of ORR. Sweet potato vines are harvested after the tubers are consumed and most of them have been ignored except for a limited use as an alternative supplement on feed intake of livestock and just released to the environment naturally or open incinerated even though they are typically rich in carbon, nitrogen, and sulfur (from threonine, lysine, and sulfur-containing amino acids). China is the leading producer of sweet potato and has an absolutely high proportion of the annual world׳s production. Herein, this work presents the cost-effective synthesis of carbon materials as highly durable ORR electrocatalyst, produced by carbonizing the wasted sweet potato vines. The absence of any activation, reasonable in-situ nitrogen and sulfur doping, porous graphitic structure along with a high surface area and excellent conductivity contribute to a superior electrocatalytic ORR activity, demonstrating a hopeful alternative for commercial Pt/C catalyst in fuel cells in terms of electrocatalytic activity, selectivity, and especially durability. Density functional theory calculations support this result. Furthermore, the specific capacitance of the as-prepared heteroatoms-doped porous carbon material is as high as 265Fg−1, with a superior cycling stability for electric double-layer supercapacitor at a current density of 1Ag−1 after 10,000 cycles, suggesting that it has a promising potential for wide applications in the field of energy storage devices. This smart transformation of organic-rich biowaste not only settles the handling issue, but also creates value-added carbon materials from the natural discard.