Relation of the electrochemical interplay between H₂PtCl₆ and H₂O/H₃O⁺/H₂⁺ and the hydrogen‐evolution reaction

Abstract

The electrodeposition of platinum from hexachloroplatinic acid solutions, on glassy carbon, was studied by developing multiple cyclic voltammetry transients. The development of an isopotential point, only observed under hydrogenevolution conditions, is postulated to be associated with the reduction of [PtCl 4 ] 2− to Pt 0 and the oxidation of the adsorbed molecular hydrogen ion (H 2 + ) ads species to (H 3 O + ) ads . The adsorption of H 2 + inhibits the continued reduction of [PtCl 4 ] 2− and the 'cleansing' of the platinum surface, that is, the removal of H 2 + through hydrogen evolution, results in the opening up of active sites to allow for the continued reduction of [PtCl 4 ] 2− on the return sweep, which results in an isopotential point (IPP). This IPP is not observed in the absence of hydrogen evolution, due to saturation of the surface by (H 2 + ) ads , and correlates with a model that explains the interplay between platinum chloride species, hydrogen containing species (H 2 O/H 3 O + /H 2 + ), and the hydrogenevolution reaction.

Atoms vs. Ions: Intermediates in Reversible Electrochemical Hydrogen Evolution Reaction

“…The twice faster diffusion of H 3 O + compared to OH − in water [45] is consistent with the presented model of H 2 ER/H 2 OR and the experimentally observed 30 mV/dec slope. Presented analysis is further supported by recent experimental results of Pt electrodeposition [18] which are explained by the mechanism involving formation of H + 2 as intermediate in reversible hydrogen evolution on Pt.…”

“…This work presents counter arguments for the commonly accepted treatment of hydrogen evolution reaction as well as arguments supporting the alternative concept of this process [17], which provides the quantitative explanation of the simultaneous charge and mass changes occurring on Pt electrode under the hydrogen evolution conditions. This revisiting view is mandated by recent experimental study, which can only explain Pt deposition on a carbon electrode via H + 2 mediation [18]. Theoretical slopes of potential vs. lg(current) are derived and compared with the reported experimental results for electrocatalytic hydrogen evolution [19][20][21].…”

The Effect of Electrolytes on the Kinetics of the Hydrogen Evolution Reaction

“…This aligns with findings in the literature on the electrocatalytic hydrogen evolution, serving as evidence for the alternative mechanism described herein. Recent experimental results on Pt electrodeposition [25] align with the presented analysis, providing support for the mechanism, involving the formation of H 2 + as an intermediate in the reversible hydrogen evolution on Pt. As the transition to the irreversible hydrogen evolution occurs, a slowdown in the formation of H 2 + in the first electron transfer stage manifests, leading to an increased slope of 2.3 RT/0.5 F ≈ 120 mV (here, R, F, and T represent the universal gas constant, Faraday constant, and absolute temperature, respectively).…”

“…Contrary to the longstanding assumption involving H ad atoms as intermediates, the study proposed that the adsorbed molecular ion (H 2 + ) ad serves as the intermediate in both HER and HOR reactions, aligning better with contemporary experimental observations. Moreover, [24] analyzed experimentally reported data with models which provide a quantitative match [25]. The analysis suggests that the reversible electrochemical hydrogen evolution (H 2 ER) occurring in acidic, neutral, and alkaline aqueous solutions can be described by one common reaction (Equation ( 14)), which involves an intermediate stage of the adsorbed hydrogen molecular ion (H 2 + ) instead of H ad as postulated in the typical Volmer-Heyrovsky-Tafel mechanism.…”

Spontaneous Deposition of Single Platinum Atoms on Anatase TiO2 for Photocatalytic H2 Evolution

“…This affinity diminishes as pH surpasses 4. Moreover, at pH >7, increased hydroxide ions lead to water molecule deprotonation, fostering the formation and subsequent adsorption of hydroxo complexes (such as [PtCl 5 (OH)] 2– , [PtCl 4 (OH)­(H 2 O)] − , and [PtCl 4 (OH) 2 ] 2– ). ,− Consequently, the presence of Pt SAs and Pt SA assemblies becomes more pronounced at pH 8, which is in close proximity to the measured PZC of the TiNSs. This observation along with the HAADF-TEM and XPS results collectively highlight the significance of the pH-dependent Pt decoration process on TiNSs, elucidating the complex interaction between surface charge, Pt adsorption, and the formation of Pt SAs and Pt SA assemblies on the surface.…”