Defect- and oxygen-rich nanocarbon derived from solution plasma for bifunctional catalytic activity of oxygen reduction and evolution reactions

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key for renewable energy systems, including metal-air batteries, fuel cells, and water electrolysis. In particular, metal-air batteries require multiple catalysts for the ORR and OER. Thus, bifunctional catalysts are required to improve efficiency and simplify catalytic systems. Hence, we developed defect- and oxygen-rich nanocarbons as bifunctional catalysts through a one-pot formation by applying plasma discharge in mixed solvents of benzene with crown ether. Raman and X-ray photoelectron spectroscopy results confirmed that oxygen was embedded and functionalized into the carbon matrix and abundant defects were formed, which highly affected the catalytic activity of the ORR and OER. The obtained CNP-CEs revealed a tuned electron transfer trend to a rapid four-electron pathway (n = 3.5) for the ORR, as well as a decreased onset potential and Tafel slope for the OER. Consequently, CNP-CE-50 exhibited an improved bifunctional catalytic characteristic with the narrowest potential gap between the ORR and OER. We believe that our findings suggest new models for carbon-based bifunctional catalysts and provide a prospective approach for a synthetic procedure of carbon nanomaterials. The embedded and functionalized oxygen with defects nano carbon structure ensured sufficient catalytic activity for the ORR and OER.

Automated summary

We developed defect- and oxygen-rich nanocarbons as bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through a one-pot formation method using plasma discharge in mixed solvents. The presence of embedded and functionalized oxygen with defects in the carbon matrix greatly influenced the catalytic activity of the ORR and OER. Our findings suggest new models for carbon-based bifunctional catalysts and provide a prospective approach for the synthesis of carbon nanomaterials.