摘要
Electrochemical H2O2 production via two-electron (2e(-)) oxygen reduction is a green onsite alternative to the current anthraquinone process. However, searching for cost-effective, metal-free electrocatalysts with high activity and selectivity toward the 2e(-) route still remains challenging. Herein we report an ionic covalent organic polymer (BPyTTz-COP:Br) that was made from the conjugation of viologen with electron-withdrawing thiazolo[5,4-d]thiazole (TTz). The polymer facilitates the adsorption of O-2 and exhibits a high H2O2 selectivity (92%) in the electrocatalytic oxygen reduction reaction. Moreover, the H2O2 selectivity of BPyTTz-COP:Br could be tuned by halide counteranion (F-, Cl-, or I-) exchange, resulting in BPyTTz-COP:X (X= F, Cl, or I). BPyTTz-COP:F showed the highest H2O2 selectivity (98.5%) among the four polymers, together with an exceptional current efficiency (97.2%) and a good durability (>10 h). Density functional theory calculations demonstrated that the H2O2 selectivity of BPyTTz-COP:X (X= F, Cl, Br and I) is correlated to the electronegativity of the corresponding halide counteranion (F > Br > Cl > I). Our work provides a strategy for designing highly efficient metal-free electrocatalysts for oxygen reduction and carbon dioxide reduction.
