Extraction of Chloride\nfrom Borated Cooling Fluid\nby Selective Electrosorption with Bismuth- and Silver-Based Electrodes

Closed-loop industrial coolants used in engines and power\nplants\nare designed to be continuously recycled and reused under harsh conditions.\nBorated coolants are utilized in reactor cooling systems of nuclear\npower plants, wherein accidental contamination of the coolant with\nchloride salts can lead to equipment corrosion and an increased risk\nof operation stoppages. Selective extraction of chloride but not boron\ncompounds is required. Herein, we demonstrate Faradaic electrodes\nbased on bismuth (BiE) or silver (AgE) that can selectively store\nchloride ions by electrosorption. Electrode compositions resulting\nin high-stability electrodes operating in nuclear plant cooling fluid\nsimulant (NFS) containing 7000 mg/L sodium pentaborate (pH 8.1–8.4)\ninclude optimum content of redox-active fillers (Bi or Ag nanoparticles\nand polypyrrole-carbon black nanoparticles, PPy-CB) and two-part thermocurable\nepoxy adhesive. The developed BiE and AgE demonstrated a chloride\nremoval capacity of up to 220 mg (BiE) and 340 mg (AgE) chloride per\ngram of active layer components, which corresponded to the complete\nconversion of available bismuth or silver to BiOCl or AgCl, respectively,\nas well as stoichiometric doping of PPy. Selectivity of the electrodes\nfor chloride ions over boron-containing anions was observed in the\n40–70 and 30–60 ranges for BiE and AgE, respectively.\nHigh cycling and storage stability of BiE operating in NFS was demonstrated.\nThe developed electrodes exhibited 100% Faradaic efficiency in chloride\nelectrosorption and storage, making them promising components for\napplication in separation batteries for selective chloride removal\nfrom the borated coolant.