The research group led by Profs. FU Qiang and BAO Xinhe from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences revealed both the geometric constraint and confinement field in two-dimensional (2D) space between a graphene overlayer and Pt(111). The researchers demonstrated a new concept of confined catalysis under 2D materials, which they have named "catalysis under cover."
These findings were published in the latest issue of PNAS, in an article entitled "Confined catalysis under two-dimensional materials."
Small spaces in nanoreactors may have big implications for chemistry. The chemical nature of molecules and reactions within nanospaces can be changed significantly due to the nanoconfinement effect. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. 2D nanoreactors formed under 2D materials can provide a well-defined model for exploring confined catalysis.
The scientists chose a graphene/Pt (111) surface as a model for studying confined catalysis using density functional theory (DFT) calculations. They showed that the adsorption of atoms and molecules on the Pt(111) surface is weakened under graphene. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. Both the geometric constraint and confinement field imposed by the 2D cover are attributed to the observed confinement phenomena.
The general tendency for weakened surface adsorption under the confinement of a graphene overlayer enables feasible modulation of surface reactions by placement of a 2D cover. The concept "catalysis under cover" can be applied to reactions between two opposite 2D walls interacting with each other through van der Waals forces. The concept helps in the design of high-performance nanocatalysts interfacing with 2D material overlayers.
The research group demonstrated the confinement-induced modulation of surface reactivity in a Pt-catalyzed oxygen reduction reaction (ORR) under 2D covers. It is known that oxygen binding to Pt is relatively strong and all means of weakening this binding can be used to promote the reaction. When placing different 2D materials such as graphene and h-BN on the surface, oxygen binding with Pt weakens, thus effectively enhancing ORR activity.
Confined catalysis under 2D materials can be applied to supported nanocatalysts. Metal nanoparticles may be encapsulated by 2D materials, thus forming core-shell nanostructures. The active core structures are well protected by the outer shells and catalyst stability is improved. Furthermore, catalyst activity can be enhanced by the confinement of the outer shells.
This study was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, and the Collaborative Innovation Center of Chemistry for Energy Materials.