Electronic Environment Tuning of Single-Atom Catalysts in CO2rr through Template- and Axial Ligand-Doping Methods

As achieving progress of meeting our climate target goals becomes more urgent, we must look to explore and further develop alternative methods of reducing not only our carbon footprint, but also the existing abundance of carbon in our atmosphere. Electrochemical CO₂ reduction (CO₂RR) has gained significant traction as a prospective method for reducing this carbon abundance. Single-atom catalysts (SACs) are very selective towards the CO₂-to-CO pathway; however, systematic studies need to be conducted to understand the mechanisms of CO₂RR on SACs if we are to achieve conversion to higher-order carbon products.

SACs are comprised of individual metal atoms coordinated to local dopant atoms embedded in a supporting template (commonly carbon-based, such as graphene), where the coordinated dopants establish a unique electronic environment around the metal, allowing the metal to act as the active site for catalysis. SACs have garnered significant interest within the research space due to both their tunable catalytic properties and their efficient use of limited metal resources. These catalyst systems can be further doped to enhance their catalytic activity and selectivity towards CO₂RR through two methods: 1) Template-doping methods, which aim to incorporate dopant atoms into the carbon template matrix for further electronic modification, and 2) Axial ligand-doping methods, which aim to coordinate ligand dopants directly to the metal active site to accomplish similar electronic tuning.

Numerous studies have investigated various template- and axial ligand-doping strategies, but very few studies have gone on to directly compare these doping strategies and resulting SAC moieties across one another, leading to difficulties in discerning which SAC moieties are the most effective for CO₂RR. Both template- and axial ligand-doping strategies are explored for two metal systems (Fe-N-C and Ni-N-C) as a starting basis. Combining electronic and structural characterization with electrochemical performance studies, we seek to understand how SACs are affected by the addition of various dopants to create a broader library for guiding the rational design of efficient CO₂RR catalysts.