Is molybdenum disulfide modified with molybdenum metal catalytically active for the nitrogen reduction reaction?

Inspired by the previously published theoretical findings, the present work aims to assess the electrocatalytic activity of molybdenum(IV) sulfide modified with metallic molybdenum for the nitrogen reduction reaction in aqueous electrolyte solution (0.1 M Li₂SO₄; pH 3) and in aprotic [C₄mpyr][eFAP] ionic liquid electrolyte at ambient temperature. The material of interest was synthesized via a high-temperature partial reduction of MoS₂, while electrocatalytic tests followed a previously established robust protocol, which in particular involves strict control over any NH₃ and NO₃⁻/NO₂⁻ contamination at every key step. As expected, no activity was found in aqueous solutions. In aprotic medium, the formation of small amounts of ammonia at low rates was observed and was found to strongly depend on the water concentration and applied potential. However, the amount of electrochemically generated NH₃ always reached a particular limit and did not increase further, even when the N₂ pressure was increased from 1 to 16 bar. The results suggest rapid blockage of the surface of the investigated electromaterial with NH₃, which prevents its operation as a catalyst for the ammonia electrosynthesis.