Construction of Atomic Metal-N₂ Sites by Interlayers of Covalent Organic Frameworks for Electrochemical H₂O₂ Synthesis

Electrosynthesis of H₂O₂ is a promising alternative to the anthraquinone oxidation process because of its low energy utilization and cost-effectiveness. Heteroatom-doped carbons-based catalysts have been widely developed for H₂O₂ synthesis. However, their doping degree, defective degree, and location of active sites are difficult to be preciously controlled at molecular level. Herein, a dioxin-linked covalent organic framework (COF) is used as the template to preciously construct different metal-N₂ sites along the porous walls for H₂O₂ synthesis. By tuning the metal centers, the catalyst with Ca-N₂ sites enables to catalyze H₂O₂ production with selectivity over 95% from 0.2 to 0.6 V versus RHE, while the H₂O₂ yields for Co sites or Ni sites are 20% and 60% in the same potential range. In addition, the turnover frequency (TOF) values for Ca-N₂ sites are 11.63 e^–1 site^–1 s^–1, which are 58 and 20 times higher than those of Co and Ni sites (0.20 and 0.57 e^–1 site^–1 s^–1). The theoretical calculations further reveal that the OOH* desorption on Ca sites is easier than those on Co or Ni sites, and thus catalyzes the oxygen reduction reaction in the 2e^– pathway with high efficiency.