Ammonia photosynthesis via an association pathway using a plasmonic photoanode and a zirconium cathode

Abstract

Most conventional photoelectrochemical-based methods for synthesizing NH₃ show low selectivity due to the generation of H₂ as a by-product. In principle, two types of reaction mechanisms can occur in the reduction of N₂ to NH₃. One is an associative pathway in which N₂ molecules on the catalyst are hydrogenated. The other is a dissociative pathway in which nitrogen and hydrogen react after the cleavage of the strong N₂ triple bond. Understanding the mechanism of NH₃ formation on the electrode will facilitate the development of selective and efficient NH₃ synthesis techniques. In this study, we constructed a two-electrode system composed of a strontium titanate photocatalytic anode in which the plasmon effect is expressed by plasmonic gold nanoparticles and a zirconium cathode, which was connected to the external circuit to investigate the reaction by electrochemical analysis in addition to analysis of the product. The bias and pH dependences of the reaction were then systematically investigated, and the plasmon-induced synthesis of NH₃ on Zr was proposed to proceed via an associative pathway.