Tuning Electrochemical Nitrogen Reduction on Metallic, 2D-MoS2 through Covalent Functionalization

Abstract

Nitrogen reduction to ammonia is one of the most energy intense reactions, requiring a dedicated, localized infrastructure. Thus, the need for a delocalized and sustainable ammonia manufacturing infrastructure is of great importance. In this regard, electrochemical nitrogen reduction to ammonia under ambient conditions would provide the opportunity to employ sustainable energy resources and make delocalized ammonia a reality. The bottleneck in implementing this technology is the unavailability of electrode materials with good activity, selectivity, and stability. A fundamental understanding on the electrode processes occurring during the nitrogen reduction reaction is of paramount importance in developing electrocatalysts. Theory has suggested edge sites, vacancy sites and phase engineered 2D MoS2 to have the ability to reduce nitrogen to ammonia. In this study, we show that covalent functionalization of metallic, 2D MoS2 to improve the catalytic activity for the reaction while suppressing the competing hydrogen evolution reaction. Using rigorous experimental protocols, we show that it is possible to record ~30% Faradaic efficiency at yield rates exceeding 20 mg/(hr mgcat) for the generation of ammonia at -50 mV vs RHE. A series of covalent molecules with varying degrees of electronegativities were employed to functionalize the metallic MoS2 surface. We show through suppressing the hydrogen evolution reaction and tuning the electronic structure of metallic MoS2 it is possible to enhance ammonia generation via heterogeneous electrocatalysis.