Extraction of Chloride from Borated Cooling Fluid by Selective Electrosorption with Bismuth- and Silver-Based Electrodes

Closed-loop industrial coolants used in engines and power plants are designed to be continuously recycled and reused under harsh conditions. Borated coolants are utilized in reactor cooling systems of nuclear power plants, wherein accidental contamination of the coolant with chloride salts can lead to equipment corrosion and an increased risk of operation stoppages. Selective extraction of chloride but not boron compounds is required. Herein, we demonstrate Faradaic electrodes based on bismuth (BiE) or silver (AgE) that can selectively store chloride ions by electrosorption. Electrode compositions resulting in high-stability electrodes operating in nuclear plant cooling fluid simulant (NFS) containing 7000 mg/L sodium pentaborate (pH 8.1–8.4) include optimum content of redox-active fillers (Bi or Ag nanoparticles and polypyrrole-carbon black nanoparticles, PPy-CB) and two-part thermocurable epoxy adhesive. The developed BiE and AgE demonstrated a chloride removal capacity of up to 220 mg (BiE) and 340 mg (AgE) chloride per gram of active layer components, which corresponded to the complete conversion of available bismuth or silver to BiOCl or AgCl, respectively, as well as stoichiometric doping of PPy. Selectivity of the electrodes for chloride ions over boron-containing anions was observed in the 40–70 and 30–60 ranges for BiE and AgE, respectively. High cycling and storage stability of BiE operating in NFS was demonstrated. The developed electrodes exhibited 100% Faradaic efficiency in chloride electrosorption and storage, making them promising components for application in separation batteries for selective chloride removal from the borated coolant.