ZnOx modified IrO2-Ta2O5 electrocatalyst with high electrochemical chlorine evolution selectivity in a wide range of pH and electrolyte concentration

Abstract

Chlorine evolution reaction (CER) is one of the most valuable electrochemical reactions in industrial application, mainly used in the chlor-alkali industry, electrochemical advanced oxidation process (EAOPs) and electrolytic antifouling technology (EAT). In these applications, the [Cl-] concentration and pH are different, so it is of great significance to develop electrode materials with high CER selectivity suitable for a wide range of pH and varying [Cl-] concentration. In this paper, ZnOx-modified IrO2-Ta2O5 (ZnOx@IrO2-Ta2O5) was prepared by the thermal decomposition combined with the oxygen-poor reactive sputtering method. By using the reactive sputtering technology, ZnOx can be successfully doped into the crystal cell of IrO2-Ta2O5, which enlarges the unit cell to a certain extent and significantly changes the electronic structure. Compared with those of IrO2-Ta2O5, the binding energy peaks of Ir4+ 4f orbitals of ZnOx@IrO2-Ta2O5 have obviously shifted negatively, which indicates that the electron has transferred to Ir. Whether in 4.0 M (pH=1.0) or 0.6 M (pH=6.88) NaCl solution, the CER activity and selectivity of ZnOx@IrO2-Ta2O5 electrode were obviously improved. In 4.0 M NaCl solution, the overpotential of 10 mA cm-2 (η10) of ZnOx@IrO2-Ta2O5 is only 60 mV with the current efficiency is 95.7%. Even in 0.6 M NaCl solution, the current efficiency can still reach 90.1%, which makes ZnOx@IrO2-Ta2O5 suitable for a wide range of pH and variable electrolyte concentration. In addition, in 4.0 M and 0.6 M NaCl solutions, their Tafel slopes are 41.75 and 49.74 mV dec-1, which indicates that their rate-determining steps (RDSs) are both the second electron transfer.