Metal free donor–acceptor covalent organic frameworks as efficient electrocatalysts for oxygen evolution reaction

Abstract

Donor–acceptor covalent organic frameworks (COFs) are gaining significant attention in electrochemical applications due to their capability to facilitate efficient charge transfer. The precise selection of donor and acceptor organic moieties might allow the customization of band structure and electronic or redox potentials, and tailoring of active catalytic sites for electrocatalysis, such as oxygen evolution reactions, where rapid electron movement reduces resistance and improves efficiency. Herein, we prepared a series of metal-free donor–acceptor COFs using pyrene, porphyrin, and diarylamine as organic building blocks. Pyrene works as a donor site, and the other organic units are acceptor sites in these π-conjugated COF systems. Redox-active porphyrin or diarylamine moieties enhance the redox properties of COF systems, and each COF has been investigated for electrocatalytic oxygen evolution reaction (OER). Among them, porphyrin-based COF catalyst demonstrates high OER activity, operating at a remarkably low overpotential of 398 mV to achieve 10 mA cm⁻² current density with a Tafel value of 89 mV dec⁻¹. The high OER activity of porphyrin-based COF can be ascribed to its high crystallinity, large surface area, and redox-active properties, in turn providing active catalytic sites for electrochemical reactions and enabling efficient ion transport for electrocatalysis. Notably, it displayed high stability in alkaline water electrolysis for up to 18 hours, realizing the high performance of the catalyst. The work highlights the strategic design of COFs for OER applications.