Electrocatalytic Reduction of Nitrogen to Ammonia Using Tiara‐like Phenylethanethiolated Nickel Cluster

Abstract

The fixing of N 2 to NH 3 is challenging due to the inertness of the N�N bond. Commercially, ammonia production depends on the energy-consuming Haber-Bosch (HÀ B) process, which emits CO 2 while using fossil fuels as the sources of hydrogen and energy. An alternative method for NH 3 production is the electrochemical nitrogen reduction reaction (NRR) process as it is powered by renewable energy sources. Here, we report a tiara-like nickel-thiolate cluster, [Ni 6 (PET) 12 ] (where, PET = 2-phenylethanethiol)] as an efficient electro-catalyst for the electrochemical NRR at ambient conditions. Ammonia (NH 3 : 16.2 � 0.8 μg h À 1 cm À 2 ) was the only nitrogenous product over the potential of À 2.3 V vs. F c + /F c with a Faradaic efficiency of 25% � 1.7. Based on theoretical calculations, NRR by [Ni 6 -(PET) 12 ] proceeds through both the distal and alternating pathways with an onset potential of À 1.84 V vs. RHE (i.e., À 2.46 V vs. F c + /F c ) which corroborates with the experimental findings.

Electrochemical dinitrogen to ammonia reduction at a nickel(ii) site: an easy access to an air-stable catalyst

“…It can be utilised as an electrocatalyst in the eNRR, which shows a FE of 26.5% with an NH 3 production rate of 36 mg h −1 cm −2 at −2.3 V vs. Fc/Fc + in a non-aqueous medium (THF), which is highest among purely Ni-based eNRR catalysts to date. 40,45 The active catalyst is a tricoordinated monomeric Ni…”

“…40,44 However, hard O 2 N donors stabilised Ni complexes are uncommon in electrochemical N 2 xation. 40,45 To our knowledge, no such system was explored for electrochemical N 2 xation. 1 can dissociate in an organic solvent to its desired monomeric form under electrochemical conditions, forming a Ni(I) intermediate.…”

“…This shows the highest FE (26.5%) in non-aqueous media for the electrochemical NRR (eNRR) to NH 3 by a Ni-based molecular cluster. 45 Using other metal centres however, a FE of over 92.5% has been reported. 27 Schiff bases are known as an inhibitor for preventing the hydrogen evolution reaction (HER) on metallic substrates.…”