Insights into transition metal encapsulated N-doped CNTs cathode for self-sufficient electrocatalytic degradation

Abstract

In electrochemical advanced oxidation processes (EAOPs), a series of transition metal encapsulated nitrogen-doped carbon nanotubes (M@N-C, M=Fe, Co, Ni, Cu) as bifunctional cathodes were synthesized to compare and uncover their activity trends, fulfilling the self-sufficient electrocatalytic degradation. The sulfamethazine (SMT) degradation activity trends were follows: Co@N-C>Fe@N-C>Ni@N-C>Cu@N-C cathode at pH≤ 7, while the Fe@N-C cathode exhibited the highest activity at pH 9 due to the more 1O2 and atomic H*. In-situ Fourier transformed infrared (FTIR) spectroscopy and density functional theory (DFT) calculation suggested that the atomic H* was easier to generate under the action of pyridinic N on Fe@N-C cathode. Overall, various pollutants degradation on Fe@N-C cathode performed with good stability with low leaching iron (0.12 mg L−1) and low energy consumption (<0.3 kWh∙log−1∙m−3). This study sheds light on different mechanisms of reactive species production on M@N-C cathode, thus providing guidance for the selectivity between M@N-C via active species and pollutants.