Promotion of nitrite and nitrate conversion into ammonia by improving *H utilization via the construction of dual active centers

Abstract

Although there has been significant progress in the research on catalysts for electrochemical reduction of nitrite and nitrate to ammonia (NO₃RR and NO₂RR, respectively), studies on economical and sustainable neutral electrolytes are still scarce. The high energy barriers associated with hydrogenation steps in neutral electrolytes result in insufficient generation and suboptimal utilization of active hydrogen (*H), which will be electrostatically repelled by the positively charged Lewis acid (LA) sites of electrocatalysts, thereby significantly lowering the faradaic efficiency (FE) and ammonia (NH₃) selectivity in the NO₂RR/NO₃RR. In this study, we proposed a specifically designed electrocatalyst with dual active sites, which performs its own functions and enables effective mitigation of the adsorption and storage issues of *H. As a prototype, W₁₈O₄₉ nanowires modified with Cu nanoparticles were constructed as electrocatalysts via pulsed laser irradiation (PLI) assembly (W–Cu–L). W atoms near oxygen vacancies serve as highly acidic LA sites, promoting the 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 a faradaic efficiency of 99.5 ± 3.7% at −0.8 V versus RHE (91.4 ± 1.3% at −1.1 V vs. RHE), along with an NH₃ yield of 1.5 ± 0.16 mmol h⁻¹ mg_cat.⁻¹ (0.93 ± 0.04 mmol h⁻¹ mg_cat.⁻¹) in the NO₂RR (NO₃RR) for neutral electrolytes. This work paves a new way for the design of multiple sites for the NO₂RR/NO₃RR in a neutral environment.