Synergistic Enhancement of Plasma-Driven Ammonia Synthesis Using a AuCu3/Cu Composite Catalyst

Abstract

Green ammonia synthesis using fluctuating renewable energy supply in decentralized process is a goal that has been long sought after. Ammonia synthesis with non-thermal plasma under mild conditions is a promising technology, but it faces the critical challenge of low energy efficiency. Herein, we develop an easily-scalable AuCu3/Cu catalyst, which consists of a decimeter-scale metallic Cu antenna and nano-scale AuCu3 catalytic sites on metallic Cu surface, significantly enhancing the energy efficiency and ammonia yield in a radio-frequency (RF) plasma system. Compared to plasma alone, the single-pass ammonia yield over AuCu3/Cu increases by a factor of 20, approaching 10%. Mechanistic studies indicate that Cu antenna can amplify the millimeter-scale local electric field, thereby facilitating the generation of active nitrogen species, including nitrogen radicals and vibration-excited nitrogen molecules. Due to the downshifted d-band center and unique Cu-Au interface structure, the AuCu3 nanoalloy modified on Cu antenna surface significantly reduces hydrogenation barriers of active NHX (x=0,1,2) species (the rate-determining step) and facilitates ammonia desorption at lower temperature. The synergistic effect of Cu antenna and surface AuCu3 nanoalloy comprehensively enhances ammonia synthesis through both the nitrogen radical-mediated Eley-Rideal pathway and the vibration-excited nitrogen molecule-mediated Langmuir-Hinshelwood pathway.