Precise Modulation of Carbon Activity Sites in Metal‐Free Covalent Organic Frameworks for Enhanced Oxygen Reduction Electrocatalysis

Abstract

Metal‐free carbon‐based materials have gained recognition as potential electrocatalysts for the oxygen reduction reaction (ORR) in new environmentally‐friendly electrochemical energy conversion technologies. The presence of effective active centers is crucial for achieving productive ORR. In this study, we present the synthesis of two metal‐free dibenzo[a,c]phenazine‐based covalent organic frameworks (DBP‐COFs), specifically JUC‐650 and JUC‐651, which serve as ORR electrocatalysts. Among them, JUC‐650 demonstrates exceptional catalytic performance for ORR in alkaline electrolytes, exhibiting an onset potential of 0.90 V versus RHE and a half‐wave potential of 0.72 V versus RHE. Consequently, JUC‐650 stands out as one of the most outstanding metal‐free COF‐based ORR electrocatalysts report to date. Experimental investigations and density functional theory calculations confirm that modulation of the frameworks' electronic configuration allows for the reduction of adsorption energy at the Schiff‐base carbon active sites, leading to more efficient ORR processes. Moreover, the DBP‐COFs can be assembled as excellent air cathode catalysts for zinc‐air batteries (ZAB), rivaling the performance of commercial Pt/C. This study provides valuable insights for the development of efficient metal‐free organoelectrocatalysts through precise regulation of active site strategies.

Advancements and applications of three-dimensional covalent organic frameworks

“…In response to the rapid societal development, the human demand for energy is surging [193] , but this heightened need, coupled with the excessive utilization of fossil fuels, has led to severe environmental pollution and an impending energy crisis [194] . Addressing these issues necessitates an improvement in energy efficiency and the exploration of cleaner energy sources [195] .…”

Insights into the origin of Co-based bimetallic catalysts with a para-structure exhibiting ORR and OER bifunctional activities

“…Therefore, developing alternative catalysts without precious metals has been widely studied. 11–16 Carbon-based materials are often used to develop efficient electrocatalysts owing to their large specific surface area, easily adjustable electronic structure, and excellent electrical conductivity, 17–19 which mainly include non-metallic atoms 20–22 and metal atoms 23–28 doped with carbon. In addition, N atoms often form coordination bonds with them to present more unique electrocatalytic properties.…”

Scalable Synthesis and Electrocatalytic Performance of Highly Fluorinated Covalent Organic Frameworks for Oxygen Reduction

“…One promising alternative for developing ORR electrocatalysts are carbon‐based nanomaterials, where non‐pyrolyzed and metal‐free COFs stand out as promising candidates due to their high stability, low toxicity, high porosity, metal‐free composition and crystallinity [14] . The latter feature is very important since it may allow to stablish structural‐property relationships to further improve the properties of COF materials for ORR catalysis [15] …”