Abstract
In this study, the processes taking place on the surfaces of nanostructured Cu/CuO and Cu/CuO/Pd electrodes at different potential, E, values in the solutions of 0.1 M KOH in H 2 O and D 2 O (heavy water) were probed by surface enhanced Raman spectroscopy (SERS), and the analysis of electrochemical reactions occurring under experimental conditions is presented. The bands of the SERS spectra of the Cu/CuO/Pd electrode observed in the range of E values from +0.3 V to 0 V (standard hydrogen electrode (SHE)) at 1328–1569 cm − 1 are consistent with the existence of species that are adsorbed or weakly bound to the surface with the energy of interaction close to 15–21 kJ mol − 1 . These bands can be attributed to the ad(ab)sorbed (H 3 O + ) ad , (H 2 + ) ab , and (H 2 + ) ad ions as intermediates in reversible hydrogen evolution and oxidation reactions (HER/HOR) taking place on the Cu/CuO/Pd electrode. There was no isotopic effect observed; this is consistent with the dipole nature of the electron-ion pair formation of adsorbed (H 3 O + ) ad and (H 2 + ) ad or (D 3 O + ) ad and (D 2 + ) ad . In accordance with the literature data, SERS bands at 125–146 cm − 1 and ∼520–565 cm − 1 were assigned to Cu(I) and Cu(II) oxygen species. These findings corroborate the quantitative stepwise mechanism of water reduction.
Highlights
IntroductionThe mechanisms of electrochemical hydrogen evolution and oxidation reactions (HER and HOR) are becoming a topic of interest again as hydrogen is expected to become the environmentally friendly fuel of the future
Thermodynamics of Hydrogen Evolution ReactionThe mechanisms of electrochemical hydrogen evolution and oxidation reactions (HER and HOR) are becoming a topic of interest again as hydrogen is expected to become the environmentally friendly fuel of the future.Appl
The first minor one at E = 0.7 V was situated in the range where reduction of CuO to Cu2 O was thermodynamically possible; the amount of charge was very low
Summary
The mechanisms of electrochemical hydrogen evolution and oxidation reactions (HER and HOR) are becoming a topic of interest again as hydrogen is expected to become the environmentally friendly fuel of the future. In [1], it was suggested that in the range of low potential values, adsorbed Had atoms are formed through a dissociative adsorption of H2 rather than the discharge of H+ ions It is defined by thermodynamics [10] that under the standard conditions, the processes of HER and HOR are described by the equation: 2H+ + 2e− H2 ,. Reaction (7) is the reduction of (H3 O+ )ad leading to the formation of the adsorbed (H2 + )ad ion and corresponds to the second reversible Langmuir-type adsorption peak, whereas Equation (8) represents the actual hydrogen evolution step on the Pt electrode, which determines the value of equilibrium potential. The correlation of the E dependence of the SERS response with the electrochemical processes taking place on the electrode surface is presented and discussed in view of the possible mechanism
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