(532cb) Spinel Cobalt Oxide As an Inexpensive, Stable and Selective Chloride Evolution Electrocatalyst in Acidic Chloride Solution

The importance of electrochemical chlorine evolution reaction (CER) lies in the fact that it produces molecular chlorine which has widespread usage in production of polymers, pesticides, insecticides, water treatment and bleaching etc. CER in acidic chloride solution, is accompanied by parasitic oxygen evolution reaction (OER) which reduces CER selectivity. In general, the expensive Ru-based electrocatalysts are used as a CER-selective electrocatalyst in acidic medium for industrial production thereby increasing the cost of the process.¹ We suggest that Ru-based electrocatalysts can be substituted by inexpensive spinel Co₃O₄ in acidic medium without compromising on CER selectivity, activity and stability. A CER selectivity of ~ 99% is achieved at low anodic potential regime (1.5 V vs RHE) at a concentration of 0.6 M NaCl in acidic medium. However, the CER selectivity reduces with the increase of electrochemical potential (>1.7 V vs RHE) suggesting the onset of OER. The CER activity and the CER selectivity increases with the increase in the concentration of NaCl. Additionally, Co₃O₄ exhibits increased stability with increase in concentration of NaCl in acidic conditions with a loss of only ~6 mV potential at a current density of 10 mA cm^-2 after a 10 h hold-test at 1.7 V vs RHE. We have correlated the increased stability of Co₃O₄ with the increased chloride adsorption layer coverage on electrocatalyst surface which inhibits both cation dissolution and formation of oxygen vacancies in the Co₃O₄ lattice structure which is supported by DFT simulation studies. Furthermore, the increase of surface coverage of chloride with the increase of brine concentration leads to the greater CER activity and increased CER selectivity and higher stability. We hope that our work will help in designing superior and inexpensive CER-selective electrocatalyst for chlor-alkali industries.

References:

1. K. B. Karlsson and A. Cornell, Chem. Rev. 116, 2982-3028, (2016)