Interfacial engineering of cobalt sulfide/graphene hybrids for highly efficient ammonia electrosynthesis

Significance Ammonia is one of the most important chemical raw materials with an annual production exceeding 200 million tons. The Haber–Bosch process is still the dominant route for industrial ammonia synthesis, which consumes 1∼3% of global annual energy production and represents a significant contributor to climate change. Electrocatalytic N2 reduction reaction is an attractive alternative candidate for carbon-free and sustainable NH3 production, but often suffers from low efficiency. Here, we developed an interfacial engineering strategy for preparing a class of strongly coupled hybrid electrocatalysts for N2 fixation. The hybrids exhibit superior N2 reduction reaction activity with a high NH3 Faradaic efficiency of 25.9% under ambient conditions. This strategy provides an approach to design advanced materials for ammonia production. Electrocatalytic N2 reduction reaction (NRR) into ammonia (NH3), especially if driven by renewable energy, represents a potentially clean and sustainable strategy for replacing traditional Haber–Bosch process and dealing with climate change effect. However, electrocatalytic NRR process under ambient conditions often suffers from low Faradaic efficiency and high overpotential. Developing newly regulative methods for highly efficient NRR electrocatalysts is of great significance for NH3 synthesis. Here, we propose an interfacial engineering strategy for designing a class of strongly coupled hybrid materials as highly active electrocatalysts for catalytic N2 fixation. X-ray absorption near-edge spectroscopy (XANES) spectra confirm the successful construction of strong bridging bonds (Co–N/S–C) at the interface between CoSx nanoparticles and NS-G (nitrogen- and sulfur-doped reduced graphene). These bridging bonds can accelerate the reaction kinetics by acting as an electron transport channel, enabling electrocatalytic NRR at a low overpotential. As expected, CoS2/NS-G hybrids show superior NRR activity with a high NH3 Faradaic efficiency of 25.9% at −0.05 V versus reversible hydrogen electrode (RHE). Moreover, this strategy is general and can be extended to a series of other strongly coupled metal sulfide hybrids. This work provides an approach to design advanced materials for ammonia production.