Oxygen Reduction Investigation on Sputtered ZnO Layers with Nano‐granular Structure

Abstract

Zinc oxide (ZnO) films with nano-granular structure were deposited by radio-frequency magnetron sputtering. The absence of preferred orientation was verified by XRD. HAADF-STEM images revealed a nanoporous structure with pore and grain sizes around 10 nm. The narrowness of the pores enabled to approximate that oxygen reduction takes place at the surface of the layers. During cathodic polarization, the surface of the electrodes became rougher due to the development of nodules on the surface. The ZnO electrodes exhibit a high activity towards oxygen reduction in KOH solution (pH = 10). Rotating ring-disk electrode measurements coupled with reaction modelling allowed to quantitatively demonstrate that the direct reduction prevailed with the indirect pathway being active as well.[a] Dr.

Impedance Spectroscopy Analysis of Structural Defects in Sputtered ZnO Films

“…The consequence of the relatively fast mechanical instability of the columnar ZnO films is that in‐depth investigation of the oxygen reduction mechanism and kinetics using collection‐based techniques, such as rotating‐ring disk electrode (RRDE) or double channel flow cell, was not possible. A recent RRDE study of ORR on the more stable nanogranular ZnO is available elsewhere …”

“…(15)). This potential was chosen since it was also selected to investigate oxygen reduction with similar films in a recent RRDE study …”

“…The global in situ information provided by EIS was completed by the local ex situ structural data at the nanoscale and microscale obtained with top‐view and cross‐sectional electron microscopy images. In the past years, some reports have demonstrated the benefits of cross‐sectional analysis (with focus ion beam or scanning transmission electron microscopy) in order to gain valuable insight on the effect of the microstructure on the protective properties of ZnO …”

“…A negative polarization was applied to the sputtered ZnO electrodes since the present study was carried out in the context of the investigation of the cathodic properties of ZnO . The cathodic activity of ZnO is still debated in the literature, as reminded by Cole in a recent review on zinc corrosion . A previous work of our group presented the electrokinetic properties of sputtered ZnO layers towards oxygen reduction …”

“…The cathodic activity of ZnO is still debated in the literature, as reminded by Cole in a recent review on zinc corrosion . A previous work of our group presented the electrokinetic properties of sputtered ZnO layers towards oxygen reduction …”