A Reflection on Sustainable Anode Materials for Electrochemical Chloride Oxidation

Abstract

Chloride oxidation is a key industrial electrochemical process in chlorine‐based chemical production and water treatment. Over the past few decades, dimensionally stable anodes (DSAs) consisting of RuO2‐ and IrO2‐based mixed‐metal oxides have been successfully commercialized in the electrochemical chloride oxidation industry. For a sustainable supply of anode materials, considerable efforts both from the scientific and industrial aspects for developing earth‐abundant–metal‐based electrocatalysts have been made. This review first describes the history of commercial DSA fabrication and strategies to improve their efficiency and stability. Important features related to the electrocatalytic performance for chloride oxidation and reaction mechanism are then summarized. From the perspective of sustainability, recent progress in the design and fabrication of noble‐metal‐free anode materials, as well as methods for evaluating the industrialization of novel electrocatalysts, are highlighted. Finally, future directions for developing highly efficient and stable electrocatalysts for industrial chloride oxidation are proposed.

Atomic Single-Layer Ir Clusters Enabling 100% Selective Chlorine Evolution Reaction

“…31 Under industrial conditions, pH values are usually ≥2 due to the limited stability of the membrane, which limits the CER selectivity of DSAs. 16 tions. 32−34 SACs can adsorb target reactants on the metal sites, 35 thereby breaking the limitation of the scaling relationship.…”

“…It is worth mentioning that the CER selectivity depends on the pH value and chloride concentration. ,, DSAs exhibit high selectivity (almost 100%) toward CER for pH < 2, particularly when the ionic strength of the electrolyte is high . Under industrial conditions, pH values are usually ≥2 due to the limited stability of the membrane, which limits the CER selectivity of DSAs . Single-atom catalysts (SACs) have exhibited impressive selectivity in many competing reactions. − SACs can adsorb target reactants on the metal sites, thereby breaking the limitation of the scaling relationship.…”

“…Bulk catalysts, like metal or metal oxide nanoparticles, usually have multiple types of adsorption sites on the surface, and it is difficult to have all active sites adsorb the target intermediates only, which provides opportunity for side reactions . The above problems are especially evident in the anode catalysts of the chlor-alkali industry. − …”

“…Chlor-alkali process is the major means to produce chlorine and caustic soda. ,− Its key reaction, chlorine evolution reaction (CER), is accompanied by oxygen evolution reaction (OER) due to the electrolysis of water, which not only causes energy waste, but also brings additional costs for gas purification. , The well-established industrial anodes, so-called dimensionally stable anodes (DSAs), , are mixtures of Ir/Ru oxides with the addition of TiO 2 as well as other dopants, such as SnO 2 and HfO 2 . ,,− OER and CER share the same oxygen sites (O site ) on noble metal oxides for reactions. According to Sabatier’s principle, the two reaction intermediates *OCl (for CER) and *OOH (for OER) have linear scaling relationship, which limits the selective catalysis of CER .…”

Thermal reconstruction engineered titanium-based gas diffusion electrodes for robust and energy-saving hydrogen hydrometallurgy

“…18,19 The thermal reconstruction method with calcination involving oxygen can make mixed metal oxides, such as RuO x , IrO x , TiO x , TaO x , etc., compact on the Ti substrates, which can stabilize the electrode at the high potentials of the harsh operation environment. [20][21][22][23][24] Based on this convenient and universal industrial approach, a new-concept Ti-based GDE is developed in this work, for which we constructed sufficient and stable metallic Pt active sites by the component regulation of the Pt, Sn, and Ti precursors (hexachloroplatinic acid, stannous chloride, and tetrabutyl titanate, respectively) on the Ti felt substrates. Aer thermal treatment at 500 °C, the metallic Pt and SnTiO x oxides were reconstructed on Ti felt (Fig.…”