Electron and proton storage on separate Ru and BaO domains mediated by conductive low-work-function carbon to accelerate ammonia synthesis

Abstract

Ammonia (NH3) has gained attention as a carbon-free fuel and hydrogen carrier, making its energy-efficient production increasingly important. Here we demonstrate that Ru and BaO, connected by conductive carbon, can separately store e− and H+, like a chemical capacitor under NH3 synthesis conditions. H atoms generated on the Ru surface by H2 activation polarize into H+/e− pairs. Subsequently, H+ migrates over the carbon surfaces to neutralize basic BaO, while e− accumulates in conductive Ru/carbon. As the work function of carbon decreases, Ru gradually becomes enriched with e−, facilitating N2 activation via π-backdonation and alleviating H2 poisoning. Thus, an optimized catalyst synthesized using N-doped MWNT with the lowest work function, exhibited 7.4 times higher activity than a reference Ba–Ru/MgO catalyst. The results show that charge distribution within catalysts can be markedly altered under reaction conditions, and its rational control can enable the design of active NH3 synthesis catalysts. Ru and Ba are common partners within ammonia synthesis catalysts, but the mechanism by which the base promotes the metal is not fully understood. Here the use of conductive carbon supports reveals intriguing mechanistic aspects of this promotion effect and enables the generation of an advanced ammonia synthesis catalyst.