Engineering the Co(II)/Co(III) Redox Cycle and Co<sup>δ+</sup> Species Shuttle for Nitrate-to-Ammonia Conversion.

Bu, Yongguang; Yu, Wenjing; Zhang, Wenkai; Wang, Chao; Ding, Jie; Gao, Guandao · Nano Lett · 2024

basic_science · Level V

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Abstract

Electroreduction of waste nitrate to valuable ammonia offers a green solution for environmental restoration and energy storage. However, the electrochemical self-reconstruction of catalysts remains a huge challenge in terms of maintaining their stability, achieving the desired active sites, and managing metal leaching. Herein, we present an electrical pulse-driven Co surface reconstruction-coupled Co<sup>δ+</sup> shuttle strategy for the precise <i>in situ</i> regulation of the Co(II)/Co(III) redox cycle on the Co-based working electrode and guiding the dissolution and redeposition of Co-based particles on the counter electrode. As result, the ammonia synthesis performance and stability are significantly promoted while cathodic hydrogen evolution and anodic ammonia oxidation in a membrane-free configuration are effectively blocked. A high rate of ammonia production of 1.4 ± 0.03 mmol cm<sup>-2</sup> h<sup>-1</sup> is achieved at -0.8 V in a pulsed system, and the corresponding nitrate-to-ammonia Faraday efficiency is 91.7 ± 1.0%. This work holds promise for the regulation of catalyst reactivity and selectivity by engineering <i>in situ</i> controllable structural and chemical transformations.