Transition Metal Chalcogenides: Perspectives on Their Applications for Nitrate Reduction

This review paper highlights the research on thrives for nitrate reduction by transition metal chalcogenides (TMCs) to produce ammonia. The exposure of humans to nitrate in the environment via public drinking water supplies is on the increase due to the elevated usage of inorganic fertilizers and animal manure in agricultural lands in various regions of the world. Many regions of the world has already set a permissible limit for nitrate in drinking water so as to prevent methemoglobinemia in children, birth defects, thyroid dysfunction and disease, various cancers, and cyanosis that culminates into asphyxia. Also, serious health disorders may occur due to ingestion of excess nitrate, such as cardiovascular disorder, genetic mutation, and diabetes. Recently, TMCs have attracted the keen interest of the scientists/researchers due to their unique tunable properties such as heterojunction formation with noble metals, morphological engineering through various synthesis techniques, elemental doping, and tunable edge active site and surface defects that induce active sites transformation at the basal planes. Irrespective of these unique surface properties, TMCs have the shortcomings of increasing surface hydrogen binding energy and Gibbs free energy change, which enhances charge-carrier separation and hydrogen evolution reaction (HER). Future research outlook should focus on the surface engineering of TMCs in terms of minimizing the formation of heterojunction, which will limit proton/electron-transfer kinetics, shifting the chemical equilibrium of HER through catalyst engineering that will mitigate the adsorption of hydrogen species, regulating the crystal phase, blocking the HER active sites, and introducing strain effects that will suppress HER and boost nitrogen reduction reaction (NRR). These strategies will suppress HER and increase the efficiency of NRR.