Construction of Atomic Metal-N 2 Sites by Interlayers of Covalent Organic Frameworks for Electrochemical H 2 O 2 Synthesis.

Electrosynthesis of H 2 O 2 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 H 2 O 2 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-N 2 sites along the porous walls for H 2 O 2 synthesis. By tuning the metal centers, the catalyst with Ca-N 2 sites enables to catalyze H 2 O 2 production with selectivity over 95% from 0.2 to 0.6 V versus RHE, while the H 2 O 2 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-N 2 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.