Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

# Hydrogen Evolution on Nano-Structured CuO/Pd Electrode: Raman Scattering Study

Version 1 : Received: 9 November 2019 / Approved: 10 November 2019 / Online: 10 November 2019 (13:53:58 CET)

A peer-reviewed article of this Preprint also exists.

Juodkazytė, J.; Juodkazis, K.; Matulaitienė, I.; Šebeka, B.; Savickaja, I.; Balčytis, A.; Nishijima, Y.; Niaura, G.; Juodkazis, S. Hydrogen Evolution on Nano-StructuredCuO/Pd Electrode: Raman Scattering Study. Appl. Sci. 2019, 9, 5301. Juodkazytė, J.; Juodkazis, K.; Matulaitienė, I.; Šebeka, B.; Savickaja, I.; Balčytis, A.; Nishijima, Y.; Niaura, G.; Juodkazis, S. Hydrogen Evolution on Nano-StructuredCuO/Pd Electrode: Raman Scattering Study. Appl. Sci. 2019, 9, 5301.

Journal reference: Appl. Sci. 2019, 9, 5301
DOI: 10.3390/app9245301

## Abstract

In this study the processes taking place on the surfaces of nanostructurized 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 the surface enhanced Raman spectroscopy (SERS) and analysis of electrochemical reactions occurring under experimental conditions is presented. Bands of the SERS spectra of Cu/CuO/Pd electrode observed in the range of $E$ values from +0.3~V to 0 V~(SHE) at 1328 - 1569~cm$^{-1}$ are consistent with the existence of species which 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$^+$)$\rm{_{ad}}$, (H$_2^+$)$\rm{_{ab}}$ and (H$_2^+$)$\rm{_{ad}}$ ions as intermediates in reversible HER/HOR processes taking place on Cu/CuO/Pd electrode. There was no isotopic effect observed; this is consistent with a dipole nature of electron-ion pair formation of adsorbed (H$_3$O$^+$)$\rm{_{ad}}$ and (H$_2^+$)$\rm{_{ad}}$ or (D$_3$O$^+$)$\rm{_{ad}}$ and (D$_2^+$)$\rm{_{ad}}$. In accordance with literature data SERS bands at 125-146~cm$^{-1}$ and $\sim 520-565$~cm$^{-1}$ were assigned to Cu(I) and Cu(II) oxygen species. These findings corroborate the mechanism of cascading reduction of water.

## Keywords

nanostructured CuO; Pd electrode; hydrogen evolution; SERS

## Subject

ENGINEERING, Energy & Fuel Technology

Comment 1
Received: 16 September 2020
Commenter: Technos
The commenter has declared there is no conflict of interests.
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