Revealing and modulating catalyst reconstruction for highly efficient electrosynthesis of ammonia.

Abstract

Electrocatalytic nitrate reduction (NO₃RR) is a promising route for sustainable ammonia synthesis under mild conditions. The widely studied Co-based catalysts undergo significant reconstruction due to nitrate oxidation and electric-field reduction during NO₃RR, leading to activity degradation. To address this issue, we develop a Co₆Ni₄ heterostructured catalyst that consists of interlaced metallic Co and Ni domains. Operando X-ray absorption spectroscopy and other in-situ characterization techniques, in conjunction with theoretical calculations, demonstrate that Ni domains function as electron reservoir, which transfer electrons to Co and prevent the accumulation of high-valence Co. Besides, the abundant Co/Ni interfaces also facilitate the NO₃RR process, thereby achieving a NH₃ Faraday efficiency of 99.21%, a NH₃ yield rate of 93.55 mg h^-1 cm^-2, and a NO₃RR stability of 120 h. Our analyses delve into the underlying causes of the observed stability of metallic Co in Co₆Ni₄ and provide compelling evidence that the discrepancy between the adsorption quantity of NO₃^- on catalyst surface and the corresponding electron supply is a pivotal factor influencing the reconstruction process.