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Ruthenium is a good catalyst for ammonia synthesis in the Haber–Bosch process and a promising electrocatalyst for electrochemical N2 reduction reaction (NRR). However, the NRR pathway on Ru is unclear because of the lack of information on reaction intermediates. Surface-enhanced infrared absorption spectroscopy combined with electrochemical measurements is employed to study the NRR mechanisms on Ru thin film. During the nitrogen reduction, the *N2Hx (0 ≤ x ≤ 2) was detected with the band of N=N stretching (∼1940 cm–1) at potentials below 0.2 V in an N2-satureated HClO4 solution. The coverage of *N2Hx on the Ru surface was significantly increased with the potential decreasing from 0.2 to −0.4 V. The formed *N2Hx species could be oxidized at potentials higher than −0.1 V. In an N2-satureated KOH solution, no N-related infrared absorption band was observed on Ru surfaces, indicating that the adsorption of nitrogen molecules on Ru surfaces is very weak.
Yao et al. (Thu,) studied this question.