A Spectroscopic Study of Electrochemical Nitrogen and Nitrate Reduction on Rhodium Surfaces

Rh is a promising electrocatalyst for the nitrogen reduction reaction (NRR) given its suitable nitrogen-adsorption energy and low overpotential. However, the NRR pathway on Rh surfaces remains unknown. In this study, we employ surface-enhanced infrared-absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanism of NRR on Rh. N₂ H_x (0≤x≤2) is detected with a N=N stretching mode at ≈2020 cm^-1 by SEIRAS and a signal at m/z=29 by DEMS. A new two-step reaction pathway on Rh surfaces is proposed that involves an electrochemical process with a two-electron transfer to form N₂ H₂ and its subsequent decomposition in the electrolyte producing NH₃ . Our results also indicate that nitrate reduction and the NRR share the same reaction intermediate N₂ H_x .