RESUMEN
Anthropogenic activities have disrupted the natural nitrogen cycle, increasing the level of nitrogen contaminants in water. Nitrogen contaminants are harmful to humans and the environment. This motivates research on advanced and decarbonized treatment technologies that are capable of removing or valorizing nitrogen waste found in water. In this context, the electrocatalytic conversion of inorganic- and organic-based nitrogen compounds has emerged as an important approach that is capable of upconverting waste nitrogen into valuable compounds. This approach differs from state-of-the-art wastewater treatment, which primarily converts inorganic nitrogen to dinitrogen, and organic nitrogen is sent to landfills. Here, we review recent efforts related to electrocatalytic conversion of inorganic- and organic-based nitrogen waste. Specifically, we detail the role that electrocatalyst design (alloys, defects, morphology, and faceting) plays in the promotion of high-activity and high-selectivity electrocatalysts. We also discuss the impact of wastewater constituents. Finally, we discuss the critical product analyses required to ensure that the reported performance is accurate.
RESUMEN
Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 µg s-1 cm-2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm-2 geo and 10 mA cm-2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.
RESUMEN
Ammonia synthesis by electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the Haber-Bosch process. Accurate measurement of produced ammonia requires rigorous criteria, which rely on a deeper understanding of ammonia characteristics. Herein, we systematically investigated the interaction of ammonia with Nafion membrane and electrolyte to reveal factors that may induce deviation in ammonia measurements. We demonstrated desirable characteristics of Nafion membrane as a separator in view of the low adsorption rate and low diffusion rate for ammonia. But one should be aware of the possible contaminants pre-existing in the membrane. It was also observed that the acid electrolyte had a much greater affinity for ammonia compared with base electrolyte. Specifically, the acid electrolyte is more vulnerable to potential ammonia contaminant in the feeding gas, whereas base electrolyte is inclined to lose produced ammonia under a continuous nitrogen flow. The findings provide a deeper understanding of ammonia's behavior in NRR test and help obtain accurate and credible ammonia measurements.