Experimental Proof of the Bifunctional Mechanism for the Hydrogen Oxidation in Alkaline Media

Abstract

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data, which provide convincing evidence for the presence of hydroxy groups on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.

Hydrogen Oxidation on Ni-Based Electrocatalysts: The Effect of Metal Doping

“…The positive effect of the surface pre-oxidation on theNi catalytic activity in HOR was also reported previously[52,63]. This observation might serve as a direct experimental evidence of the bifunctional mechanism of HOR[26,50,[64][65][66][67], when OHad species, pre-chemisorbed on the adjacent active sites, are required in order to remove Had chemisorbed on the free metallic surface of Ni, and to make the hydrogen oxidation reaction proceed.Thus, presumably a certain optimal ratio of Ni(OHad)/Ni(Had) sites is needed to retain the HOR activity of bare Ni electrocatalyst. Therefore, the theoretical estimations of HBE and OHBE, provided inFigure 1, (a)and (b), might shed some light on the understanding of the competitive co-adsorption of H and OH species (see section 2.1).…”

Improved hydrogen oxidation reaction under alkaline conditions by Au–Pt alloy nanoparticles

“…Thus, the synergistic ligand and strain effect of Au incorporation weakening hydrogen adsorption over Pt atom benefits the oxidative desorption of surface hydrogen (Volmer step: H ad + OH − → H 2 O + e − ) and consequently improves HOR activity in alkaline media [38] . Other than H adsorption on Pt sites, recent studies revealed that the adsorbed OH ads also plays an important role in HOR through the so-called bifunctional mechanism [28,39] . The CV for the adsorption/desorption of OH is shown in Fig.…”

“…E-mail addresses: huangxun@cqu.edu.cn (X. Huang), zdwei@cqu.edu.cn (Z. Wei). electrochemical reactions such as O 2 reduction reaction [25] , methanol oxidation [26] , hydrogen evolution [27] , organics oxidation reaction [28] and HOR [29] . However, the rationale for the expected improvement in both activity and kinetics with the AuPt materials in alkaline media is still a matter of controversy [30] .…”

Die Wasserstoffentwicklungsreaktion in alkalischer Lösung: Von der Theorie und Einkristallmodellen zu praktischen Elektrokatalysatoren

“…Andere Arbeitsgruppen zogen die gleiche Schlussfolgerung gestützt auf Pt‐Ru‐Nanopartikel und Pt‐Nanodrähte, die mit anderen Übergangsmetallen legiert sind . Eine Kombination elektrochemischer und In‐situ‐spektroskopischer Resultate zeigte allerdings, dass die Gegenwart von OH‐Gruppen an den Ru‐Oberflächenzentren von Ru/Pt‐Legierungen eine wesentliche Rolle bei der Förderung des geschwindigkeitsbestimmenden Volmer‐Schritts in der HOR besitzt …”