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

Highlights

• TiO₂ nanoparticle over-layer accelerate reactive chlorine generation from Ir₇Ta₃O_y.

• Uniform doping of Bi on TiO₂ further elevate current and energy efficiency.

• Surface ·OH exclusively mediate the reactive chlorine generation.

• Ratio of ·OH to higher oxide primarily determine the current efficiency.

Abstract

This study reports enhanced current (CE_RCS) and energy efficiency (EE_RCS) of reactive chlorine species (RCS) generation on Ir₇Ta₃O_y 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 CE_RCS (~100%) and EE_RCS (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.