(558bp) Suppressing the HER for the Electrochemical Synthesis of Ammonia By Using a Cu-Ag Bi-Metallic Catalyst.

Apart from storing the renewable energy in batteries, it can stored as a fuel such as hydrogen. But hydrogen storage is extremely cost intensive at present, for mobile applications. Alternatively, ammonia can be used as a hydrogen storage medium as it has a higher hydrogen storage capacity (17.65 %) than water (11.11 %). Storing ammonia is convenient and durable than hydrogen and it can be easily oxidized electrochemically to hydrogen by using renewable energy, whenever required.

The ammonia is synthesized electrochemically at ambient conditions from nitrogen and water in an alkaline medium (pH – 13.5). Along with the nitrogen reduction reaction (N₂RR), Hydrogen Evolution Reaction (HER) which is an undesired side reaction occurs. This study investigates ways of suppressing HER. An effective electrochemical cell is designed, and 3D printed for our experiments. Gas diffusion electrode (GDE) is used to improve the contact of nitrogen and the electrolyte at the catalyst interface. Copper and Silver tend to suppress HER and they are chosen for the study by electrodeposition on the GDE. Experiments were performed by varying the weight fractions of copper and silver. The resulting ammonia is quantified by UV-Visible Spectroscopy by adding Nessler’s reagent and Indo-phenol blue separately. Hydrogen is also measured using Gas Chromatography to get a qualitative understanding of the processes occurring in the system. The supplied electrolyte is recycled whereas nitrogen is continuously fed. Experiments were performed over a set of high over potentials and a set of low over potentials. The key parameters considered for the investigation are Faradaic efficiency, production rate and partial current density of ammonia. Studies were also done by recycling the resulting hydrogen produced and an increase in the Faradaic efficiency of ammonia is observed. Faradaic efficiency greater than 10% was observed when the bimetallic combinations of copper and silver are used as a catalyst.