Chemically coupled NiCoS/C nanocages as efficient electrocatalysts for nitrogen reduction reactions

Abstract

Ammonia (NH₃) as a significant industrial material as well as a clean energy carrier has become the center of attention. Using electrocatalysis to convert N₂ to NH₃ at ambient conditions is an attractive method among other sustainable methods. However, achieving high yields of NH₃ and high Faraday efficiency (FE) at a low overpotential is still a big challenge in electrocatalytic N₂ reduction reactions (NRRs). In this study, strongly chemically coupled NiCoS/C nanocages were first used for the conversion of N₂ to NH₃ in the electrocatalytic NRR. Benefiting from the unique structure and strong chemical coupling between C and NiCoS, the NiCoS/C nanocages exhibit superior NRR performance and selectivity in 0.1 M Li₂SO₄. It can achieve a high ammonia production rate of 26.0 μg h⁻¹ mg⁻¹ (2.60 μg h⁻¹ cm⁻²) and a high FE of 12.9% at 0 V (vs. RHE). Notably, with the increasing potential, the ammonia production rate could reach the highest value of about 58.5 μg h⁻¹ mg⁻¹ (5.85 μg h⁻¹ cm⁻²). The density functional theory reveals that the strong chemical coupling effect between NiCoS and C is of great importance in lowering the NRR overpotential and enhancing the electrochemical NRR activity and selectivity. This work provides a new avenue for designing the strongly chemically coupled NRR electrocatalysts to realize high NRR performance at a low overpotential.