Effect of the interfacial electric field on the HER on Pt(111) modified with iron adatoms in alkaline media

The study of the hydrogen evolution reaction (HER) aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy. In previous works, laser-induced temperature jump (LITJ) experiments on Pt(111) modified with Ni(OH)2 in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER. It was hypothesised that small amounts of Ni(OH)2 cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution. In this work, to test the validity of this hypothesis, the study has been extended to Pt(111) surfaces modified with Fe(OH)2. The modified surfaces have been studied voltammetrically, and the voltammetric charges have been analysed. The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II) to Fe(0). In agreement with the coulometric analysis, the voltammetric features in the OH adsorption region would be related with the oxidation to the +3 valence state. The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules, shifting the potential of maximum entropy away from the onset of the HER. Hence, the most catalytic surface is the one with the lowest Fe coverage.