Electrochemical Kinetics: a Surface Science-Supported Picture of Hydrogen Electrochemistry on Ru(0001) and Pt/Ru(0001)

Abstract

In this short review, we compare the kinetics of hydrogen desorption in vacuum to those involved in the electrochemical hydrogen evolution/oxidation reactions (HER/ HOR) at two types of atomically smooth model surfaces: bare Ru(0001) and the same surface covered by a 1.1 atomic layer thick Pt film. Low/high H 2 (D 2 ) desorption rates at room temperature in vacuum quantitatively correspond to low/high exchange current densities for the HOR/HER in electrochemistry. In view of the Bvolcano plot^concept, these represent two surfaces that adsorb hydrogen atoms, H ad , too strongly and too weakly, respectively. Atomically smooth, vacuum annealed model surfaces are the closest approximation to the idealized slab geometries typically studied by density functional theory (DFT). A predictive volcano plot based on DFT-based adsorption energies for the H ad intermediates agrees well with the experiments if two things are considered: (i) the steady-state coverage of H ad intermediates and (ii) local variations in film thickness. The sluggish HER/HOR kinetics of Ru(0001) allows for excellent visibility of cyclic voltammetry (CV) features even in H 2 -saturated solution. The CV switches between a H ad -and a OH ad -/O ad -dominated regime, but the presence of H 2 in the electrolyte increases the H ad -dominated potential window by a factor of two. Whereas in plain electrolyte two electrochemical adsorption processes compete in forming adlayers, it is one electrochemical and one chemical one in the case of H 2 -saturated electrolyte. We demonstrate and quantitatively explain that dissociative H 2 adsorption is more important than H + discharge for H ad formation in the low potential regime on Ru(0001).

Polycrystalline and Single‐Crystal Cu Electrodes: Influence of Experimental Conditions on the Electrochemical Properties in Alkaline Media

“…[44] Beyond Cu, such ap eak shift is observed in cyclic voltammogramso nR u(0 001) recorded in 0.1 m HClO 4 .A ccording to these results, the "Nernstian" shape of the peak at À0.15 VonC u(1 00)c ould be the formation of *OH in the negative going scan and the reoxidation to *O in the positive going scan. [45] Upon excursion to highero verpotentials (HER onset/region), *H is able adsorb on the surface by displacing *OH. This displacement of *H in turn leads to ap eak shift in the positive going scan due to kinetic limitations in *OH/*O formation on the surface.…”

Single-atom Pd-Ru pair on Pt surface for promoting hydrogen oxidation in alkaline media

“…5i). Moreover, downshift of the (d) band center reduces the filling of anti-bonding states resulting in a weaker adsorbate-surface bond and hence beneficial impact on improving the HOR kinetics of Pt in alkaline media 5,15 . Based on DFT, the (d) band center down shifts from -2.01 eV on the pristine Pt (111) surface to -2.09 eV on the Ru@Pt (111) surface, to -2.16 eV on the Pd@Pt (111), and to -2.23 eV on the Pd-Ru@Pt (111) surface.…”

Design, Synthesis and High HER Performances of 3D Ni/Mo Sulfide on Ni Foam

“…Thus, it is urgent to investigate high‐performance HER electrocatalysts with low costs. Molybdenum sulfide has been regarded as the most representative non‐precious alternative material to Pt due to its unique two‐dimensional layer structure . Its HER performance is far behind that of Pt‐based catalysts, however, because the poor conductivity and the fact that the active sites are mainly concentrated on Mo edges with only fewer ones on the plane.…”

“…Molybdenum sulfide has been regarded as the most representative non-precious alternative material to Pt due to its unique two-dimensional layer structure. [19][20][21] Its HER performance is far behind that of Pt-based catalysts, however, because the poor conductivity and the fact that the active sites are mainly concentrated on Mo edges with only fewer ones on the plane. Many approaches have been attempted to improve the catalytic activity of MoS 2 , such as morphology and structure regulation to expose more active sites, [22][23][24] introducing defects as active sites, and compositing with other materials to accelerate electron transport.…”