Main group elements in electrochemical hydrogen evolution and carbon dioxide reduction.

Main-group elements are renowned for their versatile reactivities in organometallic chemistry, including CO insertion and H activation. However, electrocatalysts comprising a main-group element active site have not yet been widely developed for activating CO or producing H. Recently, research has focused on main-group element-based electrocatalysts that are active in redox systems related to fuel-forming reactions. These studies have determined that the catalytic performances of heavier main-group element-based electrocatalysts are often similar to those of transition-metal-based electrocatalysts. Our group has recently reported the scope of including the main-group elements in the design of molecular catalysts and explored their applications in redox catalysis, such as the generation of H upon coupling of two protons (H) and two electrons (e). This feature article summarizes our research efforts in developing molecular electrocatalysts comprising main-group elements at their active sites. Furthermore, we highlight their influence on the rate-determining step, thereby enhancing the reaction rate and product selectivity for multi-H/multi-e transfer catalysis. Particularly, we focus on the performance of our recently reported molecular Sn- or Sb-centered macrocycles for electrocatalytic H evolution reaction (HER) and on how their mechanisms resemble those of transition-metal-based electrocatalysts. Moreover, we discuss the CO reduction reaction (CORR), another promising fuel-forming reaction, and emphasize the recent progress in including the main-group elements in the CORR. Although the main-group elements are found at the active sites of the molecular catalysts and are embedded in the electrode materials for studying the HER, molecular catalysts bearing main-group elements are not commonly used for CORR. However, the main-group elements assist the CORR by acting as co-catalysts. For example, alkali and alkaline earth metal ions (, Li, Na, K, Rb, Cs, Mg, Ca, and Ba) are known for their Lewis acidities, which influence the thermodynamic landscape of the CORR and product selectivity. In contrast, the elements in groups 13, 14, and 15 are primarily used as dopants in the preparation of catalytic materials. Overall, this article identifies main-group element-based molecular electrocatalysts and materials for HER and CORR.