Creating electrocatalysts for efficient CO₂ reduction to value-added products is crucial for carbon neutrality. Nanoconfinement is a promising strategy for improving the performance of these catalysts. Unlocking the factors causing it can lead to a better understanding and characterization of nanoconfinement- the first step towards smarter nanoconfined catalyst design.
A nanoconfined microenvironment is a characteristic feature of the activated silver nanoparticle/ordered ligand interlayer (Ag-NOLI) catalyst. It is created at highly negative potentials, where the repulsion faced by the ligand from the surface causes it to detach from the surface, resulting in a nanoconfined region in the metal/ligand interface. This nanoconfined region facilitates CO₂ electrochemical reduction to CO at selectivities as high as 98% compared to H₂. In this work, we use density functional theory to model the microenvironment of the Ag-NOLI catalyst and calculate the Gibbs free energies for the various reaction intermediates- *COOH and *CO. To isolate the effects of two features of nanoconfinement- the confinement distance and the chemical nature of the confining species, we used three model systems- a) a single pristine Ag surface representing the base case, b) two Ag surfaces with confinement in between, and c) the activated Ag-NOLI system with confinement between the surface and the ligand. We observed that systems containing nanoconfinement stabilize the reaction intermediates more than the single pristine Ag surface, confirming that nanoconfinement results in better performance. However, the enhancement in the Ag-NOLI system was stronger than the two Ag surfaces system, despite the nanoconfinement distance being comparable in the two cases. We attribute the difference to stronger chemical interactions in the form of hydrogen bonds in the Ag-NOLI system compared to weaker van der Waals interactions in the two Ag surfaces system. Thus, while the nanoconfinement distance plays a key role, the strength of the chemical interactions with the nanoconfining species is crucial as well. This work constitutes a first step in the systematic evaluation of the factors associated with nanoconfinement. Such characterizing studies will aid our understanding and help us design better electrocatalysts in the future.

Ethan Crumlin

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