A comparative study of RuO2 and Ru reveals the role of oxygen vacancies in electrocatalytic nitrogen reduction to ammonia under ambient conditions

Abstract

Nitrogen molecule reduction to ammonia requires adsorption and hydrogenation sites. In this study, the nitrogen reduction reaction (NRR) activity of RuO2 and metallic Ru catalysts was studied to explore the role of oxides and metallic dual active sites. Ruthenium oxide nanoparticles displayed an ammonia production rate of 16.5 & mu;g h-1 cm- 2 with a Faradaic efficiency (FE) of 0.26% at - 0.15 V vs. RHE in N2-saturated 0.1 M KOH which is 58% higher compared to Ru black (6.8 & mu;g h-1 cm- 2 with 0.19% FE at -0.15 Vvs.RHE). This is attributed to the formation of oxygen vacancies (Vo) on the RuO2 surface during cathodic potential polarization, which provides a facile adsorption site for N2 in addition to the Ru4+ active site while the proton supplied via hydrogen spillover from the metal hydride site to the adsorbed Vo-N2 site. This assumption was validated by detailed XPS, XRD, and N2 TPD analysis.Nitrogen molecule reduction to ammonia requires adsorption and hydrogenation sites. In this study, the nitrogen reduction reaction (NRR) activity of RuO2 and metallic Ru catalysts was studied to explore the role of oxides and metallic dual active sites. Ruthenium oxide nanoparticles displayed an ammonia production rate of 16.5 & mu;g h-1 cm- 2 with a Faradaic efficiency (FE) of 0.26% at - 0.15 V vs. RHE in N2-saturated 0.1 M KOH which is 58% higher compared to Ru black (6.8 & mu;g h-1 cm- 2 with 0.19% FE at -0.15 Vvs.RHE). This is attributed to the formation of oxygen vacancies (Vo) on the RuO2 surface during cathodic potential polarization, which provides a facile adsorption site for N2 in addition to the Ru4+ active site while the proton supplied via hydrogen spillover from the metal hydride site to the adsorbed Vo-N2 site. This assumption was validated by detailed XPS, XRD, and N2 TPD analysis.