46 before the analysis) and when employing catalysts containing nitrogen. In the present paper, we devised and optimized an analytical method based on ammonia ion selective electrode (ISEE, for the details see the Methods section) to determine the produced ammonia, thus the efficiency of the nitrogen reduction reaction. The ammonia ISE method was preferred to the colorimetric ones (Nessler's reagent method and indophenol blue method) as it is highly sensitive and selective in controlled experimental conditions (temperature, stirring rate, pH, ionic strength, equilibration time) and not affected by the sacrificial agents and/or byproducts.