The Impact of the Alkali Cation on the Oscillatory Electro-Oxidation of Ethylene Glycol on Platinum

The presence of hydrated alkaline cations in the supporting electrolyte has showed to play a significant role in electrocatalysis. Differently from the specific adsorption of anions, which blocks active sites and/or drive the reaction through different pathways, alkaline cations interact with adsorbed oxygenated species by non-covalent interactions. In this direction, our contribution relies on the understanding of the impact of alkaline cations in the electro-oxidation of ethylene glycol in conventional and oscillatory electrochemical conditions. We were able to extract mechanistic information of the blocking intermediates generated on the surface by the calculation of poisoning reaction rate constant (k_p) in oscillatory regime, and additionally, compared with the overall current densities in the voltammetric profiles. Paradoxically, as long as the cation hydration energy decreases (Li⁺ > Na⁺ > K⁺), larger k_p values were obtained concomitantly with higher electro-catalytic activities. Although the cation also has a blocking effect by the prevention of the reaction between adsorbed carbonaceous and oxygenated species, numerical simulations suggest that k_p is mainly related to the formation of reaction intermediates by C-C bond breaking, while the inhibition of the faradaic current comes from alkaline cations with smaller radius.