Abstract
The interface between the Pt(111) surface and several MeF/HClO4 (Me+ = Li+, Na+, or Cs+) aqueous electrolytes is investigated by means of cyclic voltammetry and laser-induced temperature jump experiments. Results point out that the effect of the electrolyte on the interfacial water structure is different depending on the nature of the metal alkali cation, with the values of the potential of maximum entropy (pme) following the order pme (Li+) < pme (Na+) < pme (Cs+). In addition, the hydrogen peroxide reduction reaction is studied under these conditions. This reaction is inhibited at low potentials as a consequence of the build up of negative charges on the electrode surface. The potential where this inhibition takes place (E inhibition) follows the same trend as the pme. These results evidence that the activity of an electrocatalytic reaction can depend to great extent on the structure of the interfacial water adlayer and that the latter can be modulated by the nature of the alkali metal cation.
Highlights
The properties of the metal|aqueous solution interphase have a key influence on the rate of electrocatalytic reactions.[1]
A reversible broad peak can be observed in the double-layer region between the hydrogen and OH adsorption/desorption regions. This feature was already observed for HClO4 + KClO4 solutions with pH values up to 3,9,10,60 and it was attributed to the reorientation of the interfacial water molecules.[9,60−62] the maximum of this peak is close to the pme for Pt(111) as determined by laser-induced temperature jump (LITJ) experiments in the mentioned conditions.[10]
It only has been noticed that in the absence or very low concentrations of alkali metal cations this feature disappears, and under these conditions, a Gouy− Chapman capacitance minimum can be observed at pH 3.63 Double-layer models including attracting ion−surface interactions site effect are under the scope to tune Gouy−Chapman capacitance within the framework of the Stern model of the interface.[64]
Summary
The properties of the metal|aqueous solution interphase have a key influence on the rate of electrocatalytic reactions.[1]. LITJ measurements in these conditions, it was demonstrated that the pme is nearly constant in the SHE scale in the whole studied pH range, with a value of 0.320 ± 0.030 V.19 These results agree with the obtained pzec values from CO displacement experiments[6] and with the estimated pzfc values from PDS reduction measurements in the same buffer conditions.[8,20] These studies allowed establishing relationships between surface charge and interfacial water structure, as well as the activity of some important electrocatalytic reactions, including the oxygen reduction reaction (ORR) and the hydrogen peroxide reduction reaction (HPRR),[21−23] hydrogen evolution and oxidation reactions (HER/HOR),[24,25] and methanol oxidation reaction (MOR).[26]. The possible differences in reactivity for the HPRR, especially on the current inhibition at low potentials, induced by changes in the interfacial water molecules as a consequence of the different present cations are investigated
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