Estudo nanogravimétrico da influência dos cátions de metais alcalinos Li+ e K+ em processos eletrocatalíticos

Electrochemical quartz crystal nanobalance (EQCN) is anin situ, low cost techniquethat has great sensibility to detect small mass changesat the electrode surface during electrochemical processes.1For a long time only covalent interactions between anions2and the electrode, that are located at the inner Helmholtz plane, were consideredas blocking the surface sitesfor electrocatalytic reactions. However, non-covalent interactions betweenhydrated alkali metal cations, atthe outer Helmholtz plane, must be consideredsincethey decrease the charge transfer rate for reactions such asthe electro-oxidation ofmethanol3,ethylene glycol4andformate5. In this work we study the interaction between lithium(Li+) or potassium (K+) and platinum surfaces by means of nanogravimetry. The results suggest Li+is a stronger inhibitor than K+for the onset of the Pt oxide formation as well as for the oxide reduction reaction (Fig. 1a). This isreflectedin a slightly larger frequency change by the adsorption ofLi+than byK+(Fig. 1b) and a minor charge transferred (Fig. 1c) in this potentialregion. Withthe interpretation of Fig. 1b we could evaluate that Li+ presents about 1.15 times more in mass than K+at the electrode surface due the stronger interaction. Besides this initial characterization, the effect of the dissolved cation was also investigated towards the electro-oxidation of small organic molecules.