Design of Thiazolo[5,4-d]thiazole-Bridged Ionic Covalent Organic Polymer for Highly Selective Oxygen Reduction to H₂O₂

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 O2 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.