The effect of electrolyte pH on the Ni-Co mixed oxides coatings produced from citrate baths

Abstract

In this work, Ni-Co oxides coatings were produced using electrochemical techniques (chronopotentiometry and/or linear voltammetry) and solutions containing Ni2+ and Co2+ ions in the molar ratio 1: 2, sodium citrate as the ligand, and different pH values (7.5 and 10.5). Energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), Raman spectroscopy (LRS) and electrochemical impedance spectroscopy (EIS) were used to characterize these coatings. The results showed that both pH values favored the production of Ni-Co oxide phases, independent of the electrochemical technique used. The EDS analysis indicated that it was possible to produce of oxides coating presenting different Ni:Co ratios using electrodeposition process. However, the morphology, the microstructure and the electrocatalytic ability of the coatings depended on both the pH and on the electrochemical technique used to produce them. The coatings produced using pH 10.5 were suitable to be used as electrocatalysts for the oxygen evolution reaction (OER).