Carbon Black Oxidized by Air Calcination for Enhanced HO Generation and Effective Organics Degradation.

Carbon black (CB) has a high conductivity and a large surface area, which are the basis of an excellent electrocatalyst. However, CB itself is usually less active or even inactive toward two-electron oxygen reduction reaction (2e ORR) due to the absence of highly active functional groups with low oxygen content. To activate commercial CB for 2e ORR, oxygen-containing functional groups were introduced onto the CB surface by a simple air calcination method. After the oxidation treatment at 600 °C (CB600), the oxygen content increased from the initial 1.17 ± 0.15 to 4.08 ± 0.60%, leading to a dramatic increase of the cathodic current from only -8.1 mA (CB) to -117.6 mA (CB600). The air cathode made of CB600 achieved the maximum HO production of 517.7 ± 2.4 mg L within 30 min, resulting in the removal of ∼91.1% rhodamine B in 2 min and an effective mineralization of ∼76.3% in an electro-Fenton reactor. This performance was much better than that obtained using the CB catalyst (65.3 ± 5.6 mg L HO production, and ∼20.3% mineralization). This excellent activity of CB600 toward 2e ORR was greatly improved by the introduction of O═C-OH and C-O-C groups. The successful improvement of the 2e ORR activity of CB using air calcination enables its practical application in electrochemical advanced oxidation processes.