Frustrated Lewis pairs on metal-cation vacancy catalysts enhanced the electroreduction of NO to NH3

Abstract

Electrocatalytic reduction of nitrogen oxide (NO_x) in the industrial flue gas to synthesize NH₃ can not only greatly improve the electrochemical efficiency of NH₃ production, but also realize the emission reduction and resource utilization of air pollutants. Purposeful structural optimization of catalysts is a key research challenge in this field. Density functional theory (DFT) calculations revealed that the formation of surface oxygen vacancies could be promoted by constructing metal cation vacancies on the catalyst surface, which in turn optimized the NO adsorption configuration and improved the catalytic activity. By this guidance, CoAl layered double hydroxide (CoAl-LDH) nanosheets containing Al atomic vacancies were prepared by alkali etching. Experimental results show that a suitable alkali etching time with aqueous NaOH can significantly enhance the electrocatalytic activity of the CoAl-LDH nanosheets for NO reduction to NH₃. Compared with pristine CoAl-LDH (0.097 mg cm⁻² h⁻¹), the NH₃ yield rate reached 0.310 mg cm⁻² h⁻¹ at −1.1 V vs. the reversible hydrogen electrode after alkali etching for 4 h, which increased by 2.2 times. Catalyst characterization and theoretical calculation results indicate that the abundant frustrated Lewis pairs (FLPs) on the surface of catalysts containing cation vacancies are the origin of the enhanced activity.