Electrocatalytic simultaneous water denitrification and green ammonia production on a commercial MoS2 catalyst

Ammonia (NH3) stands as the cornerstone of all nitrogen-based fertilizers and modern societies would be impossible without mass-scale production of this chemical. Moreover, its high energy content and density have propelled it as an alternative fuel in the pursuit of decarbonization. Yet, ammonia is currently produced via the energy-intensive Haber-Bosch process reliant on fossil fuels and so the exploration of greener synthesis techniques to meet future demands is pivotal. On the other hand, groundwater contamination by nitrate (NO3-) is a growing global concern due to its detrimental effects on the environment and human health. Addressing this challenge requires the development of novel efficient methods for nitrate removal. For this purpose electrochemical nitrate reduction reaction (E-NO3RR) has emerged as a promising technology. In this study, commercial MoS2 was evaluated for its efficacy in E-NO3RR. The experiments were conducted employing a flow cell equipped with a gas diffusion electrode (GDE), with MoS2 immobilized using an air-brushing technique. The design of experiments (DoE) and surface response methodology (RSM) were employed to explore the influence of three operational variables—operating potential, catalyst loading, and salt concentration in the electrolyte—on the Faradaic efficiency and NH3 yield of the NO3RR, as well as their potential interactions. Specifically, a 3-factors Doehlert design with three replicates of the central point was utilized. Screening experiments were initially conducted to determine the appropriate range for each variable. The results elucidate that operational potential and salt concentration in the electrolyte are the primary parameters influencing the efficacy of the E-NO3RR process. Finally, long-term stability tests were performed at the condition showing the best results.