Nitric oxide (NO) is an air pollutant, e.g., in car exhaust gas. Converting it into the relatively inert N₂ or even valuable products such as ammonia is, thus, useful. Green and sustainable electrochemical alternatives to the energy-intensive process for industrial ammonia production are attractive research targets. The electrochemical reduction of N₂ is one approach, but the chemical inertness of N₂ makes this challenging. The electrocatalytic reduction of NO could be promising for the synthesis of NH₃ due to the easier activation of NO.

Chen Chen, Shuangyin Wang, Hunan University, Changsha, China, Chandra Veer Singh, University of Toronto, Canada, and colleagues have prepared hexagonal-close-packed cobalt (hcp-Co) nanosheets to be used as catalysts for NO electroreduction. The team synthesized hcp-Co sheets from cobalt(II)chloride via a hydrothermal method. Scanning electron microscopy (SEM) showed that the hcp-Co catalyst has a nanoflower morphology composed of many small nanosheets.

The researchers evaluated the electrochemical NO reduction performance of hcp-Co in an aqueous solution of Na₂SO₄, with the catalyst powder loaded onto carbon paper and used as the working electrode. The catalyst showed a high ammonia yield of 439.50 μmol cm^–2 h^–1 and a Faraday efficiency of 72.58 %. Co nanosheets with the face-centered cubic phase (fcc-Co) showed significantly lower performance than hcp-Co. The team performed density functional theory (DFT) calculations and desorption experiments to gain further insights. Based on the results, they propose that the higher activity of hcp-Co compared with fcc-Co can be attributed to enhanced NO adsorption and improved proton diffusion.

• Hexagonal Cobalt Nanosheets for High-Performance Electrocatalytic NO Reduction to NH₃,
  Dongdong Wang, Zhi-Wen Chen, Kaizhi Gu, Chen Chen, Yingying Liu, Xiaoxiao Wei, Chandra Veer Singh, Shuangyin Wang,
  J. Am. Chem. Soc. 2023.
  https://doi.org/10.1021/jacs.3c00276