The production of ammonia (NH₃) via the Haber-Bosch process is considered energy-intensive and carbon-emissive. Electrocatalytic nitrate reduction (NO₃^-RR) powered by renewable electricity has attracted great attentions. However, it involves complex multistep deoxygenation/hydrogenation, suffers from sluggish kinetics and competing hydrogen evolution, and faces challenges in NH₃ isolation and fixation for scalable deployment.

In a study published in Angew. Chem. Int. Ed, a team led by Prof. ZHANG Linjie and Prof. HAN Lili from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a surface-reconstructed NiFe hydroxide (NiFe-LDH-R) that drives high-rate NO₃^--to-NH₃ conversion, and a membrane-free bipolar electrosynthesis configuration that delivers Faradaic efficiency exceeding 100%.

Researchers synthesized nanosheet superstructures of NiFe layered double hydroxide (NiFe-LDH) that were grown directly on a Fe foam substrate through a one-step in situ self-corrosion process at room temperature. The as-prepared NiFe-LDH was then cathodically reconstructed to form NiFe-LDH-R, in which oxygen-vacancy (Ov) clusters preferentially localized around low-valence Ni sites.

The resultant restructured NiFe-LDH (NiFe-LDH-R) demonstrated excellent concentration-universal NH₃ electrosynthesis activity in 1 M KOH, notably sustaining high Faradaic efficiencies (88.5%-95%) across a broad range and attaining an ampere-level current density as well as a remarkable yield rate.

In-situ spectroscopic analyses revealed boosted hydrogenation kinetics and a thermodynamically favorable NOH pathway for NiFe-LDH-R. Theoretical calculations indicated that synergized Ov/Fe and low-valence Ni sites respectively enhanced NO₃^- adsorption and directional active hydrogen (*H) supply, thus streamlining overall energy barriers.

Moreover, researchers established a new-style membrane-free bipolar electrosynthesis system, which enabled unprecedent NH₃ Faradaic efficiencies exceeding 100% and scalable NH₃ valorization into 4.1 g of methenamine.