| Summary: | The electrochemical advanced oxidation process is a promising technology for tackling wastewater pollution, but it suffers from poor pH adaptability and slow catalytic kinetics in a neutral and alkaline environment in a homogeneous system, as well as fast release of metal ions in a heterogeneous system. Herein, a boron- and nitrogen-codoped carbon nanotube-encapsulated transition metal (M@BN-C, M–Co, Cu) cathode with a similar structure was synthesized to explore activity trends and mechanisms. Characteristics of Co@BN-C and Cu@BN-C cathodes were examined and compared with the previously synthesized Fe@BN-C bifunctional cathode. The activity of sulfamethazine (SMT) degradation by the Co@BN-C cathode was higher than both Fe@BN-C and Cu@BN-C at pH = 3 and pH = 7, respectively. However, the activity of Co@BN-C was also higher than that of Cu@BN-C and lower than that of Fe@BN-C at pH = 9. It was observed that <sup>•</sup>OH and <sup>1</sup>O<sub>2</sub> were the main reactive oxygen species (ROS) using Co@BN-C and Cu@BN-C cathodes. The Co@BN-C generated the highest <sup>•</sup>OH for efficient SMT degradation through abundant H<sub>2</sub>O<sub>2</sub> generation, exhibiting the highest catalytic activity compared with the Cu@BN-C cathode. Overall, SMT degradation on the Co@BN-C cathode demonstrated better catalytic performance in real wastewater. This study provided insights into the fundamental catalytic trends and mechanisms of ROS production via the M@BN-C cathode, thus contributing to the development of the M@BN-C cathode for catalytic organic pollutant degradation.
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