Group VI transition
metal chalcogenides are the subject of increasing
research interest for various electrochemical applications such as
low-temperature water electrolysis, batteries, and supercapacitors
due to their high activity, chemical stability, and the strong correlation
between structure and electrochemical properties. Particularly appealing
is their utilization as electrocatalysts for the synthesis of energy
vectors and value-added chemicals such as C-based chemicals from the
CO2 reduction reaction (CO2R) or ammonia from
the nitrogen fixation reaction (NRR). This review discusses the role
of structural and electronic properties of transition metal chalcogenides
in enhancing selectivity and activity toward these two key reduction
reactions. First, we discuss the morphological and electronic structure
of these compounds, outlining design strategies to control and fine-tune
them. Then, we discuss the role of the active sites and the strategies
developed to enhance the activity of transition metal chalcogenide-based
catalysts in the framework of CO2R and NRR against the
parasitic hydrogen evolution reaction (HER); leveraging on the design
rules applied for HER applications, we discuss their future perspective
for the applications in CO2R and NRR. For these two reactions,
we comprehensively review recent progress in unveiling reaction mechanisms
at different sites and the most effective strategies for fabricating
catalysts that, by exploiting the structural and electronic peculiarities
of transition metal chalcogenides, can outperform many metallic compounds.
Transition metal chalcogenides outperform state-of-the-art catalysts
for CO2 to CO reduction in ionic liquids due to the favorable
CO2 adsorption on the metal edge sites, whereas the basal
sites, due to their conformation, represent an appealing design space
for reduction of CO2 to complex carbon products. For the
NRR instead, the resemblance of transition metal chalcogenides to
the active centers of nitrogenase enzymes represents a powerful nature-mimicking
approach for the design of catalysts with enhanced performance, although
strategies to hinder the HER must be integrated in the catalytic architecture.