(653f) Improvement of Nitrogen Reduction Reaction Via the Proton Transfer on Metal Oxide Catalysts

Ammonia is of significant chemical for human beings as it plays an essential role in chemical industries as a sustainable fertilizer. However, most NH₃ heavily depends on the Haber-Bosch process taking place under high pressure and temperature. To handle this issue, an electrochemical nitrogen reduction reaction (eNRR) under mild conditions has been a promising candidate for replacing the Haber-Bosch. However, the eNRR is well-known to be hindered by the competing hydrogen evolution reaction (HER) where many protons transform into H₂ after capturing electrons rather than reacting with nitrogen species. Hence, many researchers have focused on suppressing HER to accelerate NRR activity without H activation despite a low faradaic efficiency and NH₃ yield rate.

However, in this study, we have proposed a new mechanism that can improve NRR performance by inducing proton transfer to reactive N species, which can address the hydrogen poisoning on the surface resulting in reduced NRR activity. In other words, it means that the competitive relation between HER and NRR can be weakened by deriving the complementary relation between them. To achieve this goal, we designed diverse transition metal oxides that can promote proton migration, reducing H-poisoning on the surface during the NRR process, and suggested a unique candidate that surpasses the conventional Ru. Furthermore, to get a theoretical insight into the NRR performance from the thermodynamic and kinetic viewpoints, we newly combined density functional theory (DFT) and kinetic Monte Carlo (kMC), and successfully considered realistic reaction conditions by adding an explicit water bilayer on the surface. More specifically, first using DFT, we investigated the possibility of proton transfer for all designed structures and their overpotentials based on the thermodynamic analysis. Secondly, utilizing reaction rates available from kMC, we calculated absorbent localization, surface coverage, turnover frequency, and I-V curve according to time, temperature, and pressure.