Abstract A combined anode, Ti/IrO 2 (0–3.5 h)–Ti/RuO 2 (3.5–7 h) is designed to promote the removal of high concentration of nitrate by a stepwise method. During the electrolysis process, Ti/IrO 2 is used as anode at the first stage to promote the generation of ammonia-N and then Ti/RuO 2 is switched as anode at the next stage to enhance the chlorine evolution. The generated Cl 2 will further react with H 2 O to produce ClO − , which will oxidize ammonia-N to N 2 , therefore improve the nitrate removal efficiency. Results shown that both of the reduction of nitrate and oxidation of the by-product of ammonia-N are enhanced and the total nitrogen removal efficiency is 85% when the initial nitrate concentration is 500 mg L −1 . The avoid using cation exchange membrane not only efficiently reduces the operation cost but also simplifies the operation and maintain procedure. Graphical Abstract
The chlor-alkali process is critical to the modern chemical industry because of the wide utilization of chlorine gas (Cl 2 ). More than 95 % of global Cl 2 production relies on electrocatalytic chlorine evolution reaction (CER) through chlor-alkali electrolysis. The RuO 2 electrocatalyst serves as the main active component widely used in commercial applications. However, oxygen evolution reaction (OER) generally competes with CER electrocatalysts at RuO 2 electrocatalyst owing to the intrinsically scaling reaction energy barrier of *OCl and *OOH intermediates, leading to decreased CER selectivity, high energy consumption, and increased cost. Here, the effect of Ag doping on selective CER over RuO 2 electrocatalysts prepared by a sol–gel method has been systematically studied. We found that Ag-doping can effectively improve the Faradaic efficiency of RuO 2 electrocatalyst for CER. Furthermore, the improved CER selectivity of Ag-doped RuO 2 electrocatalysts is highly dependent on the Ag-doping concentration. The optimized Ag 0.15 Ru 0.85 O 2 electrocatalyst displays an overpotential of 105 mV along with a selectivity of 84.64 ± 1.84 % in 5.0 M NaCl electrolyte (pH = 2.0 ± 0.05), significantly outperforming undoped one (142 mV, 72.75 ± 1.52 %). Our experiments and density functional theory (DFT) calculations show electron transfer from Ag + to Ru 4+ suppresses *OOH intermediates desorption on Ag-doped RuO 2 , enabling improved CER selectivity. Such designs of Ag-doped RuO 2 electrocatalysts are expected to be favorable for practical chlor-alkali applications.
Xuefeng Zhang,Qin Yang,Zixiao Li,Wenjing Tang,Asmaa Farouk,Mohamed S. Hamdy,Yingchun Yang,Xuping Sun
The electrochemical chlorine evolution reaction (CER) is an essential and valuable technology for converting Cl − to Cl 2 in industrial-scale applications. However, under the background of freshwater scarcity, seawater electrolysis for Cl 2 generation becoming highly demanded. Meanwhile, pollutant degradation in the ocean is still challenging, especially in coastal and offshore seawaters. Herein, we provide a facile approach for constructing a highly efficient system for simultaneous Cl 2 evolution and organic contaminant abatement utilizing Co 3 O 4 nanosheet arrays decorated carbon cloth (Co 3 O 4 /CC) anode in the marine environment. The fabricated Co 3 O 4 /CC electrode achieved a considerably low potential of 1.55 V to reach a current density ( j ) of 10 mA cm −2 and long-term stability of 12 h at 100 mA cm −2 in seawater (pH = 2). Meanwhile, the practical environmental remediation results attested that the Co 3 O 4 nanosheet arrays possess an outstanding Carbamazepine (CBZ) degradation efficiency of 100 % within 6 min accompanied with a k value of 0.358 min −1 in real seawater, demonstrating the integrity and reusability. The overall findings offer new insight into designing highly active CER catalysts with efficient pollutant degradation in the marine environment.
Underwater optical instruments are subjecting marine biofouling, which leads to inaccuracy of data acquisition. In order to solve the biofouling of the optical instrument, a specific electrochemical chlorination device with highly efficient chlorine evolution reaction (CER) catalyst prepared by potentiostatic electrodeposition was designed and utilized. The catalytic activity, CER selectivity , and durability of the as-prepared CER catalyst are better than the noble metal catalysts in near-neutral seawater . Compared with the common optical glass , the application of the chlorination instrument effectively inhibits the bacterial settlement, and helps to maintain high light transmittance of the optical window. This work offers a useful strategy for the antifouling of marine optical equipment .
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