Edge-substituents and center metal optimization boosting oxygen electrocatalysis in porphyrin-based covalent organic polymers

[Display omitted] The promising non-noble electrocatalyst with well-defined structure is significant for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for the renewable energy devices like zinc-air batteries (ZABs). Herein, the four phenyl-linked cobaltporphyrin-based covalent organic polymers (COPs-1–4) with the different edge substituents (1 = −tBu, 2 = −Me, 3 = −F, and 4 = −CF3) are firstly designed and synthesized via a simple, efficient one-pot method. With the increase of electron donating capacity of the substituents, the highest occupied molecular orbital energy (EHOMO) gradually increases in the order of COP-4 COP-1 by modulating the adsorption energy of OOH* at rate-determining step (RDS) to promote ORR activity. Furthermore, introducing Ni (II) and Co (II) into porphyrin centers afford the bimetallic CoNi-COP-1 with both Co-N4, Ni-N4 active sites and edge substituted −tBu. The synergistic effect of Co, Ni bimetallic active sites and strong electron-donating −tBu substituents renders the CoNi-COP-1 the highest HOMO and smallest energy gap between the ELUMO and EF among the as-prepared five COPs, which leads to more filling electrons of its LUMO level, and thus exhibits the excellent ORR and OER bifunctional catalytic activities with an E1/2 as high as 0.85 V and an overpotential (η) of 0.34 V at 10 mA cm−2 in alkaline media, superior to monometallic Co-containing COPs-1–4. In particular, the assembled ZABs with bifunctional catalyst CoNi-COP-1 possesses high power density (94.10 mW cm−2), high specific capacity (841.71 mAh gZn−1) and long durability of over 160,000 s. This work exemplifies the rational design of pyrolysis-free non-noble metal COP-based electrocatalyst through optimizing the intrinsic metal center and its secondary coordination environment.