(509w) Self-Assembled Monolayers for Electrocatalysis: A Theoretical Study of CO2 Reduction Reaction to CO over Ag

Self-assembled monolayers (SAMs) have been used in many applications, including sensing, nanofabrication, and catalysis. 4-Mercaptobenzonitrile (4-MBN) attracts increasing interests to understand key electrochemical characteristics via the Stark effect. The delocalized electrons in 4-MBN can show stabilization effects via non-local interaction and modified electronic properties over metal surfaces, where the heterogeneous catalysis occurs. Despite the potential catalytic ability of 4-MBN SAMs, few works explore catalytic properties of 4-MBN SAMs. The catalytical electroreduction of CO₂ (CO₂RR) into valuable products provides a sustainable/carbon-neutral approach to store the renewable energy. Ag exhibits good CO₂-to-CO selectivity compared to other metallic catalysts. However, the major limitations of CO₂-to-CO over Ag are: (1)high overpotential of the initial CO₂ activation; (2) low stability of surface under-coordinated active site under high-overpotential condition. One approach is the surface modification by catalytic SAMs.

First-principles density functional theory (DFT) calculations were performed on 4-MBN/Ag systems. DFT calculations show that the presence of 4-MBN SAMs stabilized the Ag(211) facet, a high-catalytic active facet during CO₂RR-to-CO reaction (Figure 1(a)). A local high electric field near Ag induced by 4-MBN SAMs was observed and found linearly proportional to 4-MBN coverages (Figure 1(b)). The induced local electric field was able to alter electronic properties of Ag surfaces and, thus, might change thermodynamics and kinetics of the initial CO₂ activation under electrocatalytic conditions (i.e., external electric fields at the electrode/electrolyte interface). We then applied an external electric field to the CO product adsorption. With 4-MBN SAMs, dipole moment and polarizability of the CO adsorption over Ag surfaces were notably influenced as shown in Figure 1(c). Additionally, we observed that 4-MBN SAMs exhibited new organic active sites to activate CO₂ and stabilize OCOH^*. The surface stabilization effect and electronic surface modification via 4-MBN SAMs provide a new strategy for catalyst design with high efficiency and activity.