Hydrogen Evolution on Nano-StructuredCuO/Pd Electrode: Raman Scattering Study

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.

Improvement and stabilization of optical hydrogen sensing ability of Au-Pd alloys

“…2 + e for positive potentials, and facilitate a more thermodynamically favorable release H + 2 + e →H 2 (to gas) at the negative potentials; here interface reactions are considered, where the gas phase H 2 is outside of the electrode/interface while e is the electron supplied from/to the electrode. Furthermore, this reaction is reversible which is favorable for the long term stability of the sensor surface [18], and alloy function diminished due to aging can be reconstituted through annealing. The outlined methods are expected to be instrumental for improvement of all-optical detection of hydrogen aiming to enable the most sensitive and responsive monitoring of hydrogen concentration in real time.…”

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

“…In fact, formation of H ad as intermediate in the reduction of H + could be hypothesized only in the cathodic range vs E 0 2H + /H 2 = 0 V (SHE), i.e., at E < 0 V. It is noteworthy that the formation of surface hydrides (denoted as H hydr in Figure 1) can also depolarize the discharge of hydrogen ions (for details, see Appendix A in ref. [40]).…”