In-situ Raman spectroscopic studies on electrochemical oxidation behavior of chromium in alkaline solution

The electrochemical oxidation mechanism of Cr in alkaline solution was deduced by combining electrochemistry with in-situ Raman spectroscopy. • Combined electrochemistry and in-situ Raman spectroscopy to study the electrochemical oxidation behavior of chromium in the alkaline condition. • A method for the determination of chromate by chromium electrode was presented. • The method can be applied to the determination of chromate in the electroplating solution. Chromium is a metal with high hardness, and strong oxidation resistance, doping chromium in the alloy will improve the alloy's oxidation resistance and corrosion resistance. However, the mechanisms of chromium electrodeposition, electrochemical oxidation, and corrosion are still controversial and only stay in the field of electrochemical research and lack in-situ data support. Therefore, we combine electrochemistry and in-situ Raman spectroscopy to study the electrochemical oxidation behavior of Cr in 0.5 M NaOH solution. The results show that the electrochemical oxidation behavior of Cr in the alkaline solution includes two steps. The first step is that the Cr layer loses six electrons and combines with OH − oxidized to CrO 4 2− , the second step is CrO 4 2− enriched on the Cr layer, and the Cr layer loses six electrons again oxidized to Cr 2 O 7 2− . We develop an electrochemical method for CrO 4 2− concentration detection in the chromium plating solution based on this mechanism. We obtain the linear correlation curve between CrO 4 2− concentration (0.1∼2.0 mol·L −1 ) and peak current density, which has simple, fast, and broad linear range characteristics.