Effect of the Interfacial Water Structure on the Hydrogen Evolution Reaction on Pt(111) Modified with Different Nickel Hydroxide Coverages in Alkaline Media.

The hydrogen evolution reaction (HER) constitutes one of the most important reactions in electrochemistry because of the value of hydrogen as a vector for energy storage and transport. Therefore, understanding the mechanism of this reaction in relation to its pH dependence is of crucial importance. While the HER on Pt(111) works efficiently in acid media, in alkaline media, the reaction is impeded and considerably larger applied overpotentials are necessary. The presence of Ni(OH)2 adsorbed on Pt(111) has been demonstrated to highly improve the rate of hydrogen evolution, decreasing the overpotential of this reaction in comparison to acid media. The way low coverages of Ni(OH)2 on the Pt surface improve HER is still under discussion. In this work, we have prepared different Ni(OH)2 coverages on Pt(111) to check how Ni(OH)2 deposited on Pt(111) influences the HER rate. To this end, the Ni(OH)2-Pt(111)|0.1 M NaOH interface was characterized with cyclic voltammetry, CO displacement technique, and Fourier transform infrared-reflection absorption spectroscopy. On the basis of the proposal made by Ledezma-Yanez et al. [ Nature Energy 2017, 2, 17031] to explain the HER in alkaline media, we also studied the effect of the different Ni(OH)2 coverages on the electric field using the laser-induced temperature jump technique. This technique revealed that introduction of nickel adlayers on the surface decreases the ordering of the water network at the interphase, a fact that has relevant implications for the HER mechanism.