Enhanced chlorine evolution from dimensionally stable anode by heterojunction with Ti and Bi based mixed metal oxide layers prepared from nanoparticle slurry

Sukhwa Hong,Tai-Kyu Lee,Michael R Hoffmann,Kangwoo Cho

doi:10.1016/j.jcat.2020.04.009

Abstract

This study reports enhanced current (CERCS) and energy efficiency (EERCS) of reactive chlorine species (RCS) generation on Ir7Ta3Oy anode by Ti/Bi mixed metal oxide heterojunction layers despite reductions in pseudo-capacitance and film conductivity. In potentiostatic electrolysis of 50 mM NaCl solutions, dramatic improvement (0.61 mmol cm−2 hr−1 at 2.5 V NHE) was noted by simple coating of thin (~2 μm) TiO2 layer from ball-milled TiO2 nanoparticle (80–100 nm) suspension, even with moderate elevation in voltammetric wave. Decoration of Bi2O3 particles (1 – 2 μm) showed limited or adverse effects for RCS generation and stability. However, Bi-doped TiO2 layers prepared from polyol-mediated or co-precipitation methods marked the highest CERCS (~100%) and EERCS (8.16 mmol Wh−1 at 2.5 V NHE) by increased mixing level and effective shift in surface charge. Surface ·OH exclusively mediated the RCS generation whose further transformation to higher oxide could be restrained by the heterojunction layer.

Highlights

Chlorine (Cl2) is a widely utilized industrial reagent for polymer synthesis globally
This study prepared Ir7Ta3Oy Dimensionally stable anodes (DSAs) with outer heterojunction layers based on mixed bismuth citrate solution (Bi) and Ti oxide to compare the reactive chlorine species (RCS) generation efficiency during competitive OER and ClER in dilute (50 mM) NaCl solutions
Anatase dominant TiO2 layers prepared from ball-milled P60 nanoparticles brought about significantly enhanced SRRCS, CERCS, and EERCS, while TiO2-L even elevated the anodic current wave possibly owing to a tuned overall M-O bond strength

Summary

Introduction

Chlorine (Cl2) is a widely utilized industrial reagent for polymer synthesis globally. We previously proposed a heterojunction architecture with coating TiO2 layers with or without mixing Bi (BixTi1ÀxOz) on top of Ir7Ta3Oy DSA for an enhanced RCS generation in dilute aqueous solutions [11] In these configurations, conductor-like nature of IrTaOy could serve as an ohmic contact to Ti substrate [11,12], while surface hydrous TiO2 (>Ti(OH–)) provided elevated quasi-stationary concentration of >MOx(∙OH). In dilute (50 mM) NaCl solutions, the activity and selectivity for ClER were comparatively evaluated for the heterojunction anodes with variable outer layer loading (thickness) and mixing levels of Bi. In addition, the roles of >MOx(∙OH) and >MOx+1 on the RCS generation were interrogated by correlation with formate ion degradation

Preparation and characterization of the anodes

Results and discussion

Conclusions