Donor-Site-Acceptor Covalent Organic Frameworks Enable Spontaneous Nitrogen Dissociation for Boosted Photoelectrochemical Ammonia Synthesis

Photoelectrochemical (PEC) technology offers new opportunities for pushing the renewable energy-driven ammonia synthesis toward a practical level, while still facing unsatisfactory efficiency due to the obstacle of dissociating inert nitrogen triple-bonds. Herein, a novel donor-site-acceptor system is constructed in covalent organic frameworks to tackle this challenge for highly efficient PEC ammonia synthesis. Highly active boron site is elaborately embedded between the donor and acceptor units, which can be effectively activated with continuous electron flow upon photoexcitation. With the assistance of solar irradiation, the stubborn nitrogen dissociation is successfully changed from a passive endothermic reaction to a spontaneous exothermic process, completely eliminating the energy barrier of the rate-determining step and facilitating the overall reaction kinetics. The proof-of-concept system achieved an excellent PEC NRR performance with a remarkable Faradaic efficiency of 91.6%, reaching the target set by the U.S. Department of Energy (90%).