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 2 insertion and H 2 activation. However, electrocatalysts comprising a main-group element active site have not yet been widely developed for activating CO 2 or producing H 2 . 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 2 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 2 evolution reaction (HER) and on how their mechanisms resemble those of transition-metal-based electrocatalysts. Moreover, we discuss the CO 2 reduction reaction (CO 2 RR), another promising fuel-forming reaction, and emphasize the recent progress in including the main-group elements in the CO 2 RR. 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 CO 2 RR. However, the main-group elements assist the CO 2 RR by acting as co-catalysts. For example, alkali and alkaline earth metal ions ( e.g. , Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , and Ba 2+ ) are known for their Lewis acidities, which influence the thermodynamic landscape of the CO 2 RR 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 CO 2 RR.