Mixed Metal Oxide Electrodes and the Chlorine Evolution Reaction

Abstract

The chlorine evolution reaction (CER) has practical applications in the chlor-alkali industry and electrochemical wastewater treatment. Efficient, stable, and cost-effective electrodes are critical for energy efficient chlorine production, water disinfection, and wastewater treatment. These practical applications require an in-depth understanding of the catalytic mechanism of chlorine evolution, the need for lower-cost electrode materials, and improvements in electrode design at the atomic scale. Herein, we examine factors controlling activity, selectivity, and stability of alternative CER electrodes and provide mechanistic insights for achieving improvements in performance and durability. Steric effects of crystal structure and intermetallic electron polarization provide insights for understanding and tuning the electrode activity and selectivity. Additional insight into electrode deactivation mechanisms was gained by employing model material systems under controlled conditions. Herein, we explore viable strategies for the development of more efficient noble-metal-free CER electrodes for use in a variety of practical applications.

Diamond electrode facilitated electrosynthesis of water and wastewater treatment oxidants

“…The electrochemical generation of RCS has been widely investigated using mixed metal oxide electrodes [45], as well as with BDD for the synthesis of chloramines [41], and the volatile chlorine species Cl2, ClO2, and Cl2O [40]. Chloramines were observed to be efficiently synthesized via electro-oxidation of chloride anions to chlorine radicals and the subsequent chlorination of ammonia.…”

Visualization of Electrochemically Accessible Sites in Flow-through Mode for Maximizing Available Active Area toward Superior Electrocatalytic Ammonia Oxidation

“…Many efforts have been done to improve the intrinsic properties of electrocatalysts to reduce the energy barrier of chlorine evolution reaction (CER) and accelerate the reaction kinetics to decrease their activation polarization . Among all the electrocatalysts, dimensionally stable anodes (DSAs), traditionally used in the chlor-alkali industry, are considered “state-of-the-art” for active chlorine species-mediated electrocatalytic oxidation because of their excellent selectivity and stability . Most of above research has been conducted in a conventional immersed parallel-plate configuration, in which extrinsic factors become primary restrictions for energy consumption .…”

“…6 Among all the electrocatalysts, dimensionally stable anodes (DSAs), traditionally used in the chlor-alkali industry, are considered "state-of-the-art" for active chlorine species-mediated electrocatalytic oxidation because of their excellent selectivity and stability. 7 Most of above research has been conducted in a conventional immersed parallel-plate configuration, in which extrinsic factors become primary restrictions for energy consumption. 8 On the one hand, the insufficient surface area of the planar electrode limits the exposure of electrochemically accessible sites; 9 on the other hand, the mass transport of Cl − ions is severely limited by diffusion through a thick (50− 200 μm) stagnant boundary layer.…”

Electrolysis energy efficiency of highly concentrated FeCl2 solutions for power-to-solid energy storage technology

“…The research and development of the chlorine evolution anodes started in the 1950s [30] and by today resulted in the development of dimensionally stable anodes (DSA De Nora trademark, hereafter DSA®) based on titanium with a rare metal oxide coating [31,32]. DSA® is characterized by a good performance at high current densities, a low overpotential for chlorine evolution, and good selectivity for the chlorine over oxygen evolution reaction [32][33][34]. Depending on the design and type, DSA® operates at current densities up to 4 kA m −2 [35].…”

“…Depending on the design and type, DSA® operates at current densities up to 4 kA m −2 [35]. Commercially available DSA® are mostly mixed metal oxide titanium anodes with an IrO 2 − RuO 2 -TiO 2 -type coating containing one or several dopant materials [33,34,36]. They operate at the potential of about 1.36 V vs. NHE [37].…”