Phase-dependent Electrocatalytic Nitrate Reduction to Ammonia on Janus Cu@Ni Tandem Catalyst

Abstract

Electrosynthesis of NH 3 from nitrate anion (NO 3 − ) reduction (NO 3 − RR) is a cascade reaction, which is considered a great potential alternative to the Haber−Bosch route to reduce CO 2 emissions and alleviate the adverse effects of excessive NO 3 − contamination in the environment. Frequently, solid solution alloys (SSAs) with a single-phase active site may struggle to fully utilize their benefits during the entire process of nitrate (NO 3 − ) reduction, which involves multiple intermediate reactions. In this study, we showed that by separating Cu and Ni in a Janus Cu@Ni catalyst structure, we can achieve high performance in NO 3− RR, yielding a high Faradaic efficiency (92.5%) and a production rate of NH 3 (1127 mmol h −1 g −1 ) at −0.2 V versus RHE, compared to CuNi SSA (82.6%, 264 mmol h −1 g −1 ). Here, we demonstrate that a Janus Cu@Ni catalyst with shortrange ordered catalytic sites favors the adsorption of NO through a bridge-bond mode. Simultaneously, a hydrogen spillover process was observed, in which Ni dissociates H 2 O to generate *H which spontaneously migrates to adjacent catalytic sites to hydrogenate the *NO x intermediates. This facilitates N−O bond cleavage, resulting in the NH 3 production rate nearly 5 times higher than that of CuNi SSA, where NO was linearly bonded on its surface. The study of this catalytic effect, a cooperative tandem enhancement, provides insights into the design of multifunctional heterogeneous catalysts for electrochemical NH 3 synthesis.

CuCo2O4/CuO Heterostructure with Oxygen Vacancies Induced by Plasma for Electrocatalytic Nitrate Reduction to Ammonia

“…This optimization helps to promote selective nitrate reduction, thereby increasing the overall efficiency of the electrocatalytic process. By utilizing Cu-based materials, researchers aim to develop electrocatalysts that can efficiently convert nitrate ions into valuable ammonia while maintaining high selectivity and minimizing undesirable byproducts. − For instance, Wu and co-workers reported a Cu-based electrocatalyst with a low-coordinated Cu atom (Cu-LC-10) obtained by pulse laser ablation in air, which showed enhanced NO 3 RR activity. The low-coordinated Cu sites can upshift the d-band center of Cu, resulting in the enhanced adsorption of key intermediates (*NO 2 , *NO) in NO 3 RR process; meanwhile, the *NO 2 generation and hydrogenation processes were modulated, and the accumulation of NO 2 ̅ on the Cu-LC surface was also inhibited .…”

Dynamically Restructuring Nanoporous Cu–Co Electrocatalyst for Efficient Nitrate Electroreduction to Ammonia

“…Up to now, numerous nanostructured materials have been proposed as electrocatalysts for NITRR. In particular, three-dimensional nanoporous catalysts prepared by dealloying methods are characterized by their simplicity, large specific surface area, and high electrical conductivity. − Among those, cost-effective and abundant transition metals have attracted intensive attention. − The highly occupied d-orbitals in Cu have a similar energy level to the lowest unoccupied molecular π* orbital of NO 3 – , making Cu with excellent kinetics for the initial NO 3 – reduction toward nitrite (NO 2 – ) . However, the main problem is the accumulation of NO 2 – during NITRR, requiring prolonged electrolysis and high overpotential to further reduce NO 2 – to NH 3 .…”