Potassium-Promoted Formic Acid Dehydrogenation on Cu(111): Visualizing HCOO^--K⁺ Intermediates

Alkali metals play an important role in formic acid (FA) decomposition. However, the atomic-scale mechanism of how alkali metals modify FA dehydrogenation and interact with formate ions remains unclear. Here, we observed the promoting effect of potassium (K) in FA decomposition on Cu(111), using scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and temperature-programmed desorption (TPD). The presence of K can significantly promote the deprotonation of FA into protons and formate ions. The formate ions can directly coordinate with K with a maximum HCOO^--K⁺ ratio of 5:1. The HCOO^--K⁺ mixtures could further assemble into larger clusters that can remain stable at room temperature in which the K⁺ ions are bridged by formate ions. The formation of HCOO^--K⁺ mixtures could enhance the adsorption of formate ions on copper, thus facilitating the dissociation of formate ions into H₂ and CO₂ at elevated temperatures. Furthermore, we demonstrated that K⁺ plays a dominant role in promoting FA dehydrogenation compared to water due to superior ability of K⁺ to stabilize the reaction intermediate, formate. This work provides atomic-scale insights into K⁺-mediated formate stabilization on metal surfaces, offering new insights into catalytic processes involving formate species.