Dimensionally Stable Anode Research Articles

The enhancement of biodegradability index of mature landfill leachate by electrochemical oxidation process using boron-doped diamond and dimensionally stable anode

Mature solid waste landfill produces stabilized leachate with extremely low biodegradability. It renders the leachate biologically untreatable. Therefore, a pretreatment aimed to increase leachate biodegradability deems necessary prior to biological treatment. The objective of this study is to investigate the effectiveness of electrochemical oxidation process in enhancing leachate's index of biodegradability, expressed as BOD5/COD ratio. Different types of anodes were employed, namely DSA (dimensionally stable anodes) and BDD (boron-doped diamond), to represent active and non-active anode, respectively. A 2, 1.5, and 1 L leachate samples were treated in a batch recirculation reactor using an 80 mL single compartment electrochemical cell where the initial pH was set to 3, and flow rate to 5 mL s−1. The reactor was operated under constant current, with current densities of 10, 30, and 50 mA cm−2. Both DSA anode and BDD anode were successfully reached the targeted BOD5/COD ratio above 0.5, as an indication of biological treatability of pretreated leachate. The highest BOD5/COD ratio of 0.5759 and 0.5999 was obtained using BDD and DSA after 15 and 120 min, respectively, under the current density of 30 mA cm−2. Under this current density, BDD and DSA capable of removing COD up to 72% and 67%, respectively, after 4-h electrochemical oxidation.

Enhanced mechanism of 2,4-dichlorophenoxyacetic acid degradation by electrochemical activation of persulfate on Blue-TiO2 nanotubes anode

Electrochemical activation of persulfate (PS) using Blue-TiO2 nanotubes (Blue-TNT) anode was first attempted for 2,4-dichlorophenoxyacetic acid (2,4-D) decomposition with a low energy consumption of 0.14 kWh m−3, obtaining the rate constant 2.57 and 6.32 times higher than that using boron-doped diamond (BDD) anode and dimensionally stable anode (DSA), respectively. The contribution of responsible radical to 2,4-D degradation on Blue-TNT was 95% from OH while only 2% from SO4−, differing from that on BDD anode which was ascribed to both OH and non-radical oxidation. The superiority of Blue-TNT anode in PS system was certified by the apparent rate constant which was 6.4, 4.6 and 1.9 times higher than that in the NaNO3, NaClO4 and Na2SO4 electrolyte. Increasing current density and PS concentration and decreasing initial pH accelerated the removal of 2,4-D. The addition of chloride ions (Cl−) enhanced 2,4-D decay, while the presence of bicarbonate (HCO3−) and humic acid (HA) had an inhibition effect on 2,4-D degradation. Overall, electrochemical activation of PS using Blue-TNT was an effective method for contaminants degradation.

Electro-Fenton treatment of real pharmaceutical wastewater paired with a BDD anode: Reaction mechanisms and respective contribution of homogeneous and heterogeneous [rad]OH

Even though there is increasing evidence on the benefits of combining electro-Fenton (EF) and anodic oxidation with boron doped diamond anodes (BDD) for the degradation of organic pollutants, the exact contribution of OH, BDD(OH) and their synergy in the paired EF-BDD process has still not been clearly established, taking into account i) the applied current/potential; ii) the reactivity of the pollutants and their intermediates formed during treatment and; iii) the matrix effect in real wastewater. In this paper, we address the above points by conducting the EF treatment of real pharmaceutical wastewater (COD0 = 1200 mg L−1 and BOD5/COD = 0.14). In-depth data analysis revealed a synergy between homogeneous and heterogeneous BDD(OH) that accelerated the mineralization of organics, with homogeneous OH dominating during the first treatment stages, while BDD prevailed in the last stages through electron transfer reactions. EF-BDD achieved the highest mineralization yield (97.1% of TOC removal at 4.17 mA cm−2 and 0.2 mM of Fe2+), as compared to EF with a dimensionally stable anode (DSA), a material not producing heterogeneous OH. However, EF-DSA proved equally effective at increasing the biodegradability of the effluent with lower operational costs (BOD5/COD = 0.68 at US$ 1.46 m−3 in 4 h). Hence, we point out the versatility of EF to reach different targets of water quality depending upon the anode materials: EF-DSA to increase the biodegradability of refractory wastewater vs. more powerful (though costlier) EF-BDD for quasi-complete mineralization.

Treatment of high-ammonia-nitrogen landfill leachate nanofiltration concentrate using an Fe-loaded Ni-foam-based electro-Fenton cathode

Abstract In order to treat high-ammonia-nitrogen (NH3-N) landfill leachate nanofiltration concentrate (LLNC), an Fe-loaded, activated C-based Ni-foam composite electrode was prepared via ferrous ion impregnation and calcination in a nitrogen atmosphere. The composite electrode was used as a cathode and combined with a dimensionally stable anode (DSA) to form the electro-Fenton system. On the basis of single-factor experiments, a response surface methodology (RSM) was applied to evaluate the influence factors. A second-order polynomial was then obtained, and the optimum treatment conditions for the LLNC were found to include an applied voltage of 10 V, initial pH of 2.81, electrode spacing of 1.53 cm, chemical oxygen demand (COD) removal rate of 77.24 % at 300 min, and an applied voltage of 9.02 V, initial pH of 3.90, electrode spacing of 1.04 cm, and an NH3-N removal rate of 74.62 %. Three-dimensional excitation-emission matrix fluorescence spectroscopy of the LLNC before and after the electro-Fenton reaction revealed that the fluvic and humic acid-like substances, as well as the soluble microbial byproducts, were effectively removed from the LLNC. These results indicate that the electro-Fenton system can both inhibit the consumption of Fe ions and efficiently reduce the pollution indices (e.g., COD, NH3-N, and color) of LLNC without the addition of a Fenton's reagent or the production of Fe-sludge.

Treatment of landfill leachate membrane filtration concentrate by synergistic effect of electrocatalysis and electro-Fenton

To address the issues caused by the external addition of Fe in the electro-Fenton reaction, activated carbon catalysts loaded with Fe were prepared by an impregnation method with which a novel Fe-activated carbon-titanium mesh composite air cathode (Fe/AC/Ti cathode) was prepared. The preparation conditions were investigated and determined in terms of chemical oxygen demand (COD) removal efficiency of the nanofiltration concentrate of landfill leachate (LLC). An electrochemical system constructed using the Fe/AC/Ti cathode and a dimensional stable anode (DSA) was developed to treat the LLC. The electrochemical reaction conditions were studied by single-factor experiments and orthogonal array analysis. The highest COD removal (97.06 %) was obtained at an applied voltage of 10 V, initial pH of 7, and electrode distance of 1 cm. The optimum conditions were applied voltage of 8 V, initial pH of 3, and electrode distance of 3 cm for 61.24 % total organic carbon removal. BOD5/COD ratios of all tests increased from 0.03 to between 0.23 and 0.51. The effluent after the reaction was either neutral or weakly alkaline. Neither hydrogen peroxide nor Fe ions were added to the reaction system, and almost no Fe precipitation was produced. The system realized the co-treatment of Cl-containing wastewater by anodic electrocatalytic oxidation and cathode electro-Fenton in the same reactor. We also address this common problem in the electro-Fenton reaction utilizing a simple low-cost method with abundant source-material.

Electrochemical oxidation of reverse osmosis concentrates using enhanced TiO2-NTA/SnO2-Sb anodes with/without PbO2 layer

The traditional dimensional stable anodes (Ti/SnO2-Sb, Ti/PbO2) have poor electrochemical properties for further practical application. In this study, we fabricated two types of anodes for the treatment of reverse osmosis concentrates (ROCs). These two anodes were fabricated based on the enhanced nanotube array (ENTA) as internal structure. One anode is only coated by SnO2-Sb layer on the ENTA (Ti-ENTA/SnO2-Sb), while the other one is coated by SnO2-Sb layer and plus PbO2 layer (Ti-ENTA/SnO2-Sb/PbO2). It was found that the ENTA improved the electrochemical properties (e.g., oxygen evolution potential, HO• production) of the anodes. The conversion service lifetime of novel anodes were enhanced greatly than the traditional one. Then, we found that Ti-ENTA/SnO2-Sb anode has superior electro-catalytic than Ti-ENTA/SnO2-Sb/PbO2. In the range of current density of 5–20 mA cm−2, the COD removal rate of ROCs for Ti-ENTA/SnO2-Sb anode and Ti-ENTA/SnO2-Sb/PbO2 anode were 0.12–0.23 mg min−1 and 0.11–0.19 mg min−1, respectively. Finally, we comprehensively compared the current efficiency and cost of ROCs degradation among various anodes. It was mentioned that novel anodes require lower energy cost (~6.1 $/kg COD) during electrochemical process. Overall, electrochemical process is a cost-effective process and a very promising technology for practical application.

Ultrathin multilayer Sb-SnO2/IrTaOx/TiO2 nanotube arrays as anodes for the selective oxidation of chloride ions

The oxidation of chloride ions (Cl − ) to oxidized chlorine species (chlorine/hypochlorous acid/hypochlorite) is emerging as a promising alternative to the oxygen evolution reaction because it has a lower overpotential than the latter, and can also produce value-added anodic products. Here, an ultrathin multilayer electrode (Sb-SnO 2 /IrTaO x /TiO 2 nanotube (TNT)) has been fabricated by simple dipping and electrodeposition methods for the production of hypochlorous acid by Cl − oxidation. The use of non-noble metal-based electrodes significantly reduced the use of noble metals and increased the selectivity for Cl − oxidation even at the neutral pH and low concentration of NaCl, resulting in the reduction of cost and energy consumption. The nanotube structure of Sb-SnO 2 /IrTaO x /TNT affords an increased active surface area and loading amounts of the catalysts compared to the structure of the flat electrodes, making the Sb-SnO 2 /IrTaO x /TNT more efficient than flat electrodes for Cl − oxidation. The Faradaic efficiency of Sb-SnO 2 /IrTaO x /TNT for Cl − oxidation was ∼95%, indicating that water oxidation was almost suppressed. Compared to the commercial dimensionally stable anode (DSA), the overpotential of Sb-SnO 2 /IrTaO x /TNT for water oxidation is much larger than for Cl − oxidation, therefore, the Sb-SnO 2 /IrTaO x /TNT could exhibit the high selectivity for Cl − oxidation by suppressing the competitive water oxidation. • Ultrathin multilayer electrode has been fabricated as an anode for Cl − oxidation. • Sb-SnO 2 /IrTaO x /TiO 2 nanotube reduced the use of noble metals. • Sb-SnO 2 catalyst layer increased the selectivity for Cl − oxidation at neutral pH. • The Faradaic efficiency for Cl − oxidation was ∼95% by suppressing water oxidation at neutral pH.

Degradation of thiocyanate by electrochemical oxidation process in coke oven wastewater: Role of operative parameters and mechanistic study

This study presents the removal of thiocyanate (SCN−) from coke oven wastewater by the electrooxidation (EO) process. Initially, the performances boron-doped diamond (BDD) and different DSA (Dimensionally stable anode) electrodes including Ti/IrO2, Ti/IrO2−RuO2, and Ti/IrO2−RuO2−TiO2 in SCN− removal were compared. BDD anode outperformed the Ti−based mixed metal oxide (MMO) anodes achieving 96.51% SCN− removal efficiency. The most favorable conditions for the removal of SCN− using BDD anode were determined as follows: pH = 9, current density = 43.10 A m−2, and the electrolyte concentration (Na2SO4) = 2.5 g L−1. The strong role of ⦁OH in the removal of SCN− was confirmed by the addition of radical quenching agents. The evolution of the intermediates as a result of the EO of SCN− was determined. Under the determined conditions, the EO process could remove 84.13% of SCN− and 94.67% of phenol from a real coke oven wastewater, which was comparable to that of the simulated solution. The electrical energy consumption cost of the process to remove 1 kg of SCN− was calculated as 0.208 US $. Overall, the study showed the EO using BDD anode is a cost-effective method for the removal of SCN− from a coke oven wastewater.

Effect of Flow Rate on Electrochemical Oxidation of Landfill Leachate Using DSA and BDD Anode

The leachate produced in municipal mixed waste landfill contains mostly organic pollutants in various forms. Biological treatment that popularly applied for the treatment only capable of removing biodegradable portion of the organics whilst the recalcitrant parts will leave the system untreated. Therefore, a pretreatment prior to biological process to increase biodegradability of leachate is essential. The physicochemical method such as electrochemical oxidation is an appropriate pretreatment alternative because it has high efficiency in degrading such pollutants. The purpose of this study was to examine the effect of flow rate (1.5 and 5 mL s−1) and anodes (boron-doped diamond (BDD) and dimensionally stable anode (DSA)) on the efficiency of electrochemical oxidation process to degrade leachate. The parameters analyzed were COD, BOD, ratio of BOD5/COD (biodegradability index, BI), TDS and pH. The results showed that the increase in BI when BDD and DSA used were 0.386 and 0.179, respectively. The best COD removal was achieved by BDD and DSA at current density of 30 mA cm−2 with the flow rate of 5 mL s−1. BDD could remove 83 % COD (1.56 g) while DSA 68 % (1.08 g) with specific energy consumption of 0.00268 kWh g−1 and 0.00186 kWh g−1, respectively.

Amorphous Iridium and Tantalum Oxide Layers Coated on Titanium Felt for Electrocatalytic Oxygen Evolution Reaction

The layer of electrocatalytic mixed oxides is known as a dimensionally stable anode (DSA) used in many industrial electrochemical processes. A layer of iridium oxide (IrO2) and tantalum oxide (Ta2O5) coated on a titanium (Ti) substrate electrode is active for oxygen evolution reaction (OER) in acidic solution. Herein, we used a porous Ti felt composed of microfibers as a conductive substrate for the IrO2-Ta2O5 electrocatalytic layer. The effect of the Ti substrates and the calcination temperature on the electrocatalytic activity for OER was investigated by cyclic voltammetry in an acidic sulfate solution. The results show that the IrO2-Ta2O5 layer on the porous Ti felt with a large surface area was more active than the layer on the conventional Ti plate. The electrocatalytic activity of IrO2-Ta2O5 layers was maximized by calcination at 350 °C and decreased by increasing the calcination temperature with the decrease of the double-layer capacitance (Cdl), which is recognized as an electrochemically active surface area (ECSA). The IrO2-Ta2O5 thin layer on the Ti felt was amorphous in the measurement of X-ray diffraction and Raman spectroscopy. The amorphous layer was confirmed to have rare cracks, larger ECSA, and higher catalytic activity for OER. The overpotential required to reach the current density of 10 mA cm–2 was only 0.27 V. The constant current was the Faradaic current for water oxidation to evolve O2.

Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients

In this work, the transformation of urine into nutrients using electrolytic oxidation in a single-compartment electrochemical cell in galvanostatic mode was investigated. The electrolytic oxidation was performed using thin film anode materials: boron-doped diamond (BDD) and dimensionally stable anodes (DSA). The transformation of urine into nutrients was confirmed by the release of nitrate (NO3−) and ammonium (NH4+) ions during electrolytic treatment of synthetic urine aqueous solutions. The removal of chemical oxygen demand (COD) and total organic carbon (TOC) during electrolytic treatment confirmed the conversion of organic pollutants into biocompatible substances. Higher amounts of NO3− and NH4+ were released by electrolytic oxidation using BDD compared to DSA anodes. The removal of COD and TOC was faster using BDD anodes at different current densities. Active chlorine and chloramines were formed during electrolytic treatment, which is advantageous to deactivate any pathogenic microorganisms. Larger quantities of active chlorine and chloramines were measured with DSA anodes. The control of chlorine by-products to concentrations lower than the regulations require can be possible by lowering the current density to values smaller than 20 mA/cm2. Electrolytic oxidation using BDD or DSA thin film anodes seems to be a sustainable method capable of transforming urine into nutrients, removing organic pollution, and deactivating pathogens.

Degradation of oxamic acid using dimensionally stable anodes (DSA) based on a mixture of RuO2 and IrO2 nanoparticles

Dimensionally stable anodes (DSA) have been widely used to degrade organic compounds because these surfaces promote the electrogeneration of active chlorine species in the bulk of the solution, as well as in the vicinity of the anode when NaCl is used as supporting electrolyte. In this work, the nanoparticles synthesis of IrO2 and RuO2 was performed to obtain two types of DSA electrodes named Class I and II to degrade oxamic acid. For Class I and II DSA, the nanoparticles used were synthesized separately and in the same reaction medium, respectively. Electrolysis were carried out in an open cylindrical cell without division at 25 °C, DSAs were used as anodes and a stainless-steel electrode as cathode, both elements have a geometric area of 2.8 cm2 immersed in 0.05 mol L−1 of NaCl or Na2SO4 and a current density of 3 mA cm−2 was applied for 6 h. Active chlorine species generated in the absence of oxamic acid in NaCl were also detected and quantified through ion chromatography. In Na2SO4 there was no degradation of the compound, but in NaCl the oxamic acid concentration reaching 85% with Class I DSA. The same tendency is observed in mineralization, in which Class I DSA allowed reaching a CO2 transformation close to 73%. The difference in the results occurs because with Class I DSA, more hypochlorite is generated than with Class II and therefore there is a larger amount of oxidizing species in the solution that enables the degradation and mineralization of oxamic acid.

Degradation of organics in real oil sands process water by electro-oxidation using graphite and dimensionally stable anodes

The effectiveness of electro-oxidation (EO) using graphite anode and dimensional stable anode (DSA) for the degradation of organics in real oil sands process water (OSPW) was investigated and the performances of the two anodes were compared. EO by graphite anode was able to reduce the chemical oxygen demand (COD), acid extractable fractions (AEF), classical and oxidized naphthenic acids (NAs) and aromatics in OSPW even at current density as low as 0.5 mA/cm2. The removal of organics by DSA started when the current density reached 2 mA/cm2. The removal of classical NAs by both anodes increased with the increase in the applied current density and was always higher than the removal of AEF. Graphite anode showed higher NA and AEF removals than DSA at current densities below 20 mA/cm2. The reactivity of NAs in OSPW toward oxidation on both anodes increased with the increase in the cyclicity and carbon number. EO by DSA generated low-carbon number NAs as byproducts of the oxidation of high-carbon NAs. Graphite anode maintained higher current efficiency at all applied current densities. Both anodes were able to remove the aromatic compounds, with DSA being more selective toward aromatics especially those with multiple aromatic rings, which were removed completely at 20 mA/cm2 after 90 min. The results indicated that graphite anode is more effective for OSPW treatment at lower current densities, while DSA shows better performance at higher current densities.

Electrochemical activation of persulfate on BDD and DSA anodes: Electrolyte influence, kinetics and mechanisms in the degradation of bisphenol A

The combination of electrolysis and persulfate (PS) activation was investigated to enhance the degradation of bisphenol A (BPA) using boron-doped diamond (BDD) and dimensional stable anode (DSA) in perchlorate, sulfate, and chloride media. The acceleration effect of BPA degradation followed the order of Cl−>ClO4−>SO42- in BDD/PS and BDD system, while the degradation order in DSA/PS and DSA system was Cl−>SO42->ClO4−. The contribution of radical species (SO4− and OH), active chlorine and electrolysis were confirmed for the degradation in different media with PS. Active chlorine dominated the degradation process with 85 % and 60 % removal in BDD/PS and DSA/PS system at 10 min, while the contribution of SO4− decreased from 20 % and 18 % in perchlorate to 5 % and 6 % in chloride media, respectively. The aromatic intermediates resulting from hydroxylation and carboxylation pathway and chlorinated products via hydroxylation and chlorine substitution pathway were detected in perchlorate and chloride media in BDD/PS system, respectively. The attempt of BDD/PS system in actual wastewater indicated potential for further application. This study aims to provide a deep insight to comprehensively understand the enhanced performance, contributions of different removal mechanisms, and degradation pathway of pollutants during the activation of PS in BDD and DSA systems in different media.

Heterogeneous Model To Distinguish the Activity of Electrogenerated Chlorine Species from Soluble Chlorine in an Electrochemical Reactor

The formation of active chlorine species on dimensionally stable anodes (DSA) has been used for the treatment of recalcitrant organic compounds contained in wastewater, whereby the present study develops a heterogeneous model thoroughly describing the surface electrochemistry of this mechanism arising in a FM01-LC reactor on Sb2O3-doped Ti/RuO2–ZrO2 anodes. The model accounts for fluid mechanics, mass transport, and kinetics of electrogenerated active chlorine according to the predominance (i.e., HClO species), being able to describe variations in current density and inlet flow rates. These results are compared against a classical homogeneous model to stand out the impacts of adsorbed chloride species and particularly remark deviations in concentration, current efficiency, and pH from experimental data. Experimental HClO concentration, current efficiency, and pH are substantially better simulated by the heterogeneous mechanism, denoting the role of adsorbed chlorine species during chloride oxidation on DSA.

Optimized terbium doped Ti/PbO2 dimensional stable anode as a strong tool for electrocatalytic degradation of imidacloprid waste water.

The presence of pesticides in water has emerged as a momentous environmental issue over the past decades. Herein, a terbium doped Ti/PbO2 (denoted as Ti/PbO2-Tb) dimensionally stable Ti/PbO2-Tb anode has been successfully prepared by one-step electrodeposition path for electrocatalytic degradation of imidacloprid (IMD) wastewater with high efficiency. Ti/PbO2-Tb electrode presents higher oxygen evolution potential, lower charge transfer resistance, stronger stability, longer service lifetime and outstanding electrocatalytic activity than Ti/PbO2 electrode. The optimum condition for IMD oxidation is obtained by analyzing the effects of some critical operating parameters including temperature, initial pH, current density and electrolyte concentration. It is proved that 70.05% of chemical oxygen demand and 76.07% of IMD are removed after 2.5 h of degradation under current density of 8 mA cm-2, pH 9, temperature 30 °C and 7.0 g L-1 NaCl electrolyte. In addition, the electrode displays commendable energy saving property as well as favorable reusability. The degradation mechanism of IMD is proposed by analyzing the intermediates identified by LC-MS. The present research provides a feasible strategy to degrade IMD wastewater by Ti/PbO2-Tb electrode.

Inactivation of Rhizoctonia solani in fertigation water using regenerative in situ electrochemical hypochlorination

The capture and re-use of greenhouse fertigation water is an efficient use of fertilizer and limited water resources, although the practice is not without risk. Plant pathogens and chemical contaminants can build up over successive capture and re-use cycles; if not properly managed they can lead to reduced productivity or crop loss. There are numerous established and emerging water treatment technologies available to treat fertigation water. Electrochemical processes are emerging as effective means for controlling pathogens via in situ regenerative hypochlorination; a process that is demonstrated here to achieve pathogen control in fertigation solutions without leading to the accumulation of potentially phytotoxic free chlorine residuals associated with other chlorination processes. An electrochemical flow cell (EFC) outfitted with ruthenium dioxide (RuO2) dimensionally stable anodes (DSA) was characterized and evaluated for free chlorine production and Rhizoctonia solani inactivation in both irrigation and fertigation solutions. Pathogen inactivation was achieved at low current densities and short residence or cell contact times. Effluent free chlorine concentrations were significantly lower than commonly reported phytotoxic threshold values (approximately 2.5 mg/L) when fertilizer (containing ammonium) was present in the test solution; an effect attributable to reactions associated with breakpoint chlorination, including chloramine formation, as well as the presence of other oxidizable compounds in the fertilizer. Chloride concentrations were stable under the test conditions suggesting that the EFC was operating as a regenerative in situ electrochemical hypochlorination system. No significant changes to macronutrient concentrations were found following passage through the EFC.

Electrochemical removal of nitrate from a Donnan dialysis waste stream.

The objective of this work was to investigate electrochemical removal of nitrate from a high salinity waste stream generated by Donnan dialysis. Donnan dialysis for nitrate removal is a promising technique. It produces a distinctive composition of a high salinity waste stream of NaCl or Na2SO4 that requires a viable disposal method. The waste stream has the full anionic composition of contaminated groundwater, but the only cation is sodium. Experiments were conducted in a batch system setup. A copper cathode was chosen over brass, aluminum and graphite cathodes. A dimensionally stable anode (DSA), Ti/PbO2, was selected over a Ti/Pt anode. Electrochemical denitrification of high salinity Donnan dialysis nitrate wastes was successfully achieved, with different behavior exhibited in high salinity NaCl solution than in high salinity Na2SO4 solution. NaCl inhibited nitrate removal at high salinities while Na2SO4 did not. The maximum removals after 4 h operation in the high salinity wastes were 69 and 87% for the NaCl and Na2SO4 solutions respectively.

Enhancing the Selectivity between Oxygen and Chlorine towards Chlorine during the Anodic Chlorine Evolution Reaction on a Dimensionally Stable Anode

AbstractThe selectivity of the chlorine evolution reaction over the oxygen evolution reaction during the electrolysis of aqueous NaCl is, despite being very high, still insufficient to prevent expensive separation of the formed Cl2 and O2 by means of liquefaction. We hypothesize that, by decreasing the local activity of H2O near the anode surface by substantially increasing the ionic strength of the electrolyte, the oxygen evolution reaction would be suppressed, leading concomitantly to a higher selectivity of Cl2 over O2 formation. Hence, the influence of the ionic strength on the competition between electrochemical evolution of O2 and Cl2 at dimensionally stable anodes (DSAs) was investigated. Addition of a high concentration of NaNO3, an inert electrolyte additive, increases the selectivity for chlorine at high current density, as determined by means of online electrochemical mass spectrometry and UV‐vis spectroscopy. We propose conditions in which free water is suppressed, owing to under‐coordination of the solvation shells of ions, as a general concept to modulate the selectivity of competing electrochemical reactions.

Corrosion modeling of dimensional stable anode modified by graphene compounds through a response surface methodology

The corrosion behavior of a titanium-based electrode with an electrocatalytic coating of TiO2-RuO2 modified by graphene oxide (GO)/reduced graphene oxide (rGO) nanosheets synthesized via a sol-gel method, has been investigated. For this purpose, the central composite design method (CCD) and surface response methodology (RSM) were used to simulate and optimize the graphene compounds additives and the layers of the coating on the linear polarization resistance (LPR) of a dimensionally stable anode (DSA). Also, significant parameters and their interactions were investigated. In order to characterize the synthesized coatings, XRD, FE-SEM, TEM, AFM, potentiodynamic polarization, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) curves were used. The optimal conditions includes the GO concentration of 1.0 mg ml−1, rGO concentration of 0.55 mg ml−1 and the layers of 4, demonstrated the optimal predicted LPR equal to 682.55 kΩ cm−2 and the mean value for the synthesized optimal electrode equal to 694.27 kΩ cm−2, which indicated that the model was suitable and reliable for analyzing the effect of the input parameters on the corrosion resistance of the anodes. The contribution of graphene into the coatings composition increases the corrosion resistance due to the layered structure of nanosheets. On the other hand, by distraction, the penetration of electrolyte to the substrate through the pores, the formation of the middle layer of TiO2 is prevented, which is the main cause of the deactivation of DSAs.