The Promotion of Nitrite and Nitrate Conversion into Ammonia by Improving *H Utilization via the Construction of Dual Active Centers

Abstract

Although the research on electrochemical reduction of nitrite and nitrate to ammonia (NO3RR/NO2RR) catalysts has made significant progress, the process of economical and sustainable neutral electrolytes is still scarce. The high energy barriers associated with hydrogenation steps in neutral electrolyte results in insufficient generation and suboptimal utilization of active hydrogen (*H), which will be electrostatically repelled by the positively charged Lewis acid (LA) sites of the electrocatalysts, thereby significantly hindering the Faradaic efficiency (FE) and ammonia (NH3) selectivity in NO2RR/NO3RR. In this paper, we proposed a kind of specifically designed dual active sites, which perform their own functions and enable effective mitigation of the adsorption and storage issues of *H. As a prototype, W18O49 nanowires modified with Cu nanoparticles were constructed as electrocatalyst via pulsed laser irradiation (PLI) assembly (W-Cu-L). The W atoms near oxygen vacancies serve as highly acidic LA sites, promoting adsorption of NO3− and NO2− and Cu nanoparticles (NPs) act as *H generation centers, favoring electron transfer from W18O49 via the Schottky junction. Meanwhile, the low free energy barrier for *H generation at Cu sites, coupled with the high energy barrier for the transition of *H → H2, underscores the *H storage capability of Cu sites. Accordingly, the well-built junction of W-Cu-L exhibited Faradaic efficiency of 99.5 ± 3.7% at – 0.8 V versus RHE (91.4 ± 1.3 % at –1.1V vs RHE), along with NH3 yield of 1.5 ± 0.16 mmol h−1 mgcat.−1 (0.93 ± 0.04 mmol h−1 mgcat.−1) in NO2RR (NO3RR) for neutral electrolyte. This work paves a new way to design multiple sites for NO2RR/NO3RR of neutral environment.