(439f) High Resolution Atomic Force Microscopy Study of an Immobilized Molecular CO2 Reduction Electrocatalyst

Recently, Wang et al. [1,2] have found a promising class of catalysts for CO₂ conversion to methanol based on immobilized cobalt phthalocyanine (CoPc) derivatives. It was found that both the support and the CoPc functionalization strongly impacted both activity and selectivity to methanol. Carbon monoxide adsorption strength is considered the key descriptor in methanol selectivity and thus it has been posited that the support and functionalization allow the CO adsorption to be tuned for an optimal balance between activity and selectivity towards the desired methanol product. To investigate this possibility at the single molecule level, we have begun applying non-contact atomic force microscopy (NC-AFM) to CO interactions with CoPc derivatives adsorbed on different surfaces; this talk focuses on CoPc on Ag(111). It was found that all of the CoPc molecules adsorb in equivalent configurations on the Ag surface. By tethering a CO molecule to the end of the tip, the molecular structure of the catalyst could be imaged. Moreover, the three-dimensional AFM method was applied with the CO functionalized tip to obtain quantitative force and potential energy maps of the interaction between the tethered CO molecule and CoPC. From this data, maps of equilibrium distances and potential energies at these distances could be generated. In addition, by simultaneously measuring the tunneling current decay, variations in the work function were imaged which provide insight into the charge transfer and distribution around the molecule. Continuing work is focusing on how these interactions are influenced by CoPc substituents, the supporting surface and proximity to defects, e.g. steps.

[1] Y. Wu, Z. Jiang, X. Lu, Y. Liang, and H. Wang, Nature, 2019, 575, 639.

[2] X. Zhang et al., Nature Communications, 2017, 8, 14675.