Combining Voltammetry and Ion Chromatography: Application to the Selective Reduction of Nitrate on Pt and PtSn Electrodes

Abstract

To overcome the shortcomings of electro-analytical methods in analyzing the ionic reaction products that are either electrochemically inert or lack distinct electrochemical/spectroscopic fingerprints, we suggest combining voltammetry with ion chromatography by applying online sample collection to the electrochemical cell and offline ion chromatographic analysis. This combination allows a quantitative analysis including the potential dependence of the product distribution in a straightforward way. As a proof-of-concept example, we discuss the formation of ionic reaction products from nitrate reduction on Pt and Sn-modified Pt electrode in acid. On the Pt electrode, ammonia was the only identifiable product. After Sn modification of the Pt electrode, a change in selectivity was observed to hydroxylamine as the dominant product. Moreover, the rate determining step of nitrate reduction (reduction to nitrite) was enhanced by Sn modification of the Pt electrode, and a significant concentration of nitrite was evidenced on a Pt electrode with a high coverage of Sn species. The suggested combination of voltammetry and online ion chromatography hence proves very useful in the quantitative elucidation of electrocatalytic reactions with different ionic products.