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This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm−2. They also reached maximum power densities of 1.2 mW cm−2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion. [ABSTRACT FROM AUTHOR]

In this work, a series of novel mixed metal oxide (MMO) electrodes with the composition Ti/RuO2Sb2O4Ptx (0 ≤ x ≤ 10.0) were developed, envisaging their application in a reversible electrochemical cell based on the chloralkaline process as an energy storage system. These electrodes were synthesized via the ionic liquid method. Comprehensive physical, chemical, and electrochemical characterizations were conducted to evaluate their performance. The feasibility of employing these electrodes within reversible processes was explored, using the products generated during the electrolytic operation of the system for fuel cell operation. During the electrolyzer operation, higher current densities resulted in enhanced current efficiencies for the production of oxidized chlorine species. Notably, the presence of platinum in the catalyst exhibited a negligible impact on the coulombic efficiency at low current densities where water oxidation predominates. However, at higher current densities, the presence of platinum significantly improved coulombic efficiency, approaching values of approximately 60%. Transitioning to a fuel cell operation, despite the improved kinetic performance associated with a higher platinum content, the process efficiency was predominantly governed by ohmic losses. Curiously, the MMO electrode made without platinum (Ti/(RuO2)70-(Sb2O4)30) displayed the lowest ohmic losses. This study establishes optimal conditions for future investigations into this promising possibility, which holds great potential for energy storage via chloralkaline-based reversible reactions. [ABSTRACT FROM AUTHOR]

BACKGROUND: This work focuses on the electrochemical production of chlorate solutions for direct use and integration in the manufacture of chlorine dioxide (ClO2), from the perspective of manufacturing portable ClO2 electrochemical generators. RESULTS: Chlorate production was evaluated from the oxidation of sodium chloride (NaCl) contained in brackish solutions (20 g L−1) and brines (200 g L−1) in single chamber flow electrochemical cells. Efficiency in chlorate ion (ClO3−) production increased with temperature and NaCl concentration, but the use of brackish solutions led to a higher quality product, as compared to the brines, with lower concentration of chlorine and hypochlorous acid. To evaluate the production of ClO2, samples corresponding to two different qualities of the electrogenerated solutions underwent stripping to exhaust chlorine, before being mixed with hydrogen peroxide (H2O2) and sulfuric acid. Results showed that using a chlorate solution obtained from the electrolysis of 20 g L−1 NaCl solution at 50 mA cm−2 and passing 57.35 Ah L−1, a maximum concentration of 33.3 mmol L−1 ClO2 could be attained, which corresponds to a maximum conversion of 48.75%. CONCLUSIONS: Efficiency of the synthesis depends on both the purity of chlorate and the H2O2/ClO3− ratio. This confirms that in‐situ electrogenerated chlorate can be used to manufacture ClO2, but there are still many gaps to be overcome and further work must be carried out to optimize the production of the desired oxidant in a portable ClO2 device. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

With the final purpose of manufacturing electrochemically-based devices that produce chloride dioxide efficiently, this paper focuses on the production of chlorates and hydrogen peroxide in two different electrochemical cells, in which operation conditions are selected to obtain high efficiencies, and in the subsequent combination of both electrochemically manufactured solutions to produce chlorine dioxide. Results demonstrate that suitable reagents can be produced by electrolyzing 20 g L−1 sodium chloride solutions at 50 mA cm−2 and 50 °C, and 3000 mg L−1 NaClO4 solutions at 5.0 mA cm−2 and 15 °C with current efficiencies of 30.9% and 48.0%, respectively. Different tests performed with these electrolyzed solutions, and also with commercial hydrogen peroxide and chlorate solutions, demonstrate that the ratio between both reagents plays a very important role in the efficiency in the production of chlorine dioxide. Results clearly showed that, surplus chlorate should be contained in the reagent media to prevent further reduction of chlorine dioxide by hydrogen peroxide and consequently, loses of efficiency in the process. During the reaction, a gas with a high oxidation capacity and consisting mainly in chloride dioxide is produced. The results contributed to the maximum conversion reached being 89.65% using electrolyzed solutions as precursors of ClO2, confirming that this technology can be promising to manufacture portable ClO2 devices. [ABSTRACT FROM AUTHOR]

In this work, the electrochemical oxidation of gaseous streams polluted with three different volatile organic compounds (benzene, toluene, and p-xylene, known as BTX) was evaluated using a jet mixer and electrochemical cell device. Efficiency reached by this technology in the production of hydrogen peroxide was 14% at atmospheric pressure and 12 °C. Results demonstrate the suitability of electrochemically assisted absorption for the treatment of this polluted streams. In the electrolytic assisted absorption (ELAA), keeping a ratio gas flowrate / current intensity of 20 L h−1 A−1, removal efficiencies of 3.14, 1.59, and 0.88 mmol A−1 h−1 were attained for benzene, toluene, and p-xylene, respectively. These values increased up to 12.00, 3.26 and 1.15 mmol A−1 h−1, respectively, when Fe (2+) salt was added to the electrolyte solution to promote the formation of the Fenton reagent, pointing out the higher efficiencies reached by the electro-Fenton assisted absorption (EFAA). The transient response of the systems lasted after four hours of operation and the concentration of pollutants absorbed in the electrolyte decreased in the sequence benzene > toluene > p-xylene (because of their solubility in aqueous solutions) and in the sequence of processes physical absorption (PA) > electrolytic assisted absorption (ELAA) > electro-Fenton assisted absorption (EFAA) (because of the reactivity). Only very low concentrations of carboxylic acids (oxalic and malonic) were accumulated in the absorbent during the process, pointing out that mineralization of these VOCs was the primary reaction pathway. [Display omitted] • The jet electrochemical cell equipped with flow-through electrodes degrades VOCs. • Removals of up to 3.14 mmol A−1 h−1 for BTX with electrolytic assisted absorption. • Removals of up 12.00 mmol A−1 h−1 for BTX with electro-Fenton assisted absorption. • Very low concentrations of intermediates point out mineralization. • Oxalic and malonic acid as primary intermediates. [ABSTRACT FROM AUTHOR]

The European Union is studying the possibility of prohibiting the use of fluorinated-based materials which could limit the use of the most studied and used Nafion and Nafion-like membranes for any applications. Therefore, this study focuses on the preparation and performance evaluation of green, non-fluorinated proton exchange membranes in a chlor-alkali-based reversible electrochemical cell system for renewable energy storage applications. The membranes were prepared by casting and cross-linking of polyvinyl alcohol (PVA) with varying chitosan (CS) concentrations (5–20 wt%), followed by sulfonation using diluted sulfuric acid at room temperature. CS concentrations significantly influenced membrane's physicochemical properties, including ion exchange capacity, ionic conductivity, mechanical strength, and water uptake. Positron annihilation lifetime spectroscopy revealed a correlation between free volume properties and other membrane characteristics. A custom-designed 3D-printed electrochemical cell was developed, capable of operating in reversible mode (both electrolysis and fuel cell modes) with a zero-gap configuration. The PVA/CS (20 wt%) membrane outperformed Nafion, exhibiting a lower voltage (4 V vs. 6 V) in electrolysis mode at 50 mA cm⁻2 and a higher specific power density (2.7 vs. 1.9 mW cm⁻2 mgPt) in fuel cell mode. The obtained results demonstrate that crosslinked PVA/CS non-fluorinated based membranes can be sulfonated using diluted sulfuric acid and work effectively in reversible chlor-alkali electrochemical cells. • Cross-linked PVA/CS membranes were successfully sulphonated with dilute H₂SO₄. • High CS content improves ion exchange capacity, water absorption, and conductivity. • High Chitosan (CS) concentrations weaken the mechanical properties. • A strong correlation between PALS analysis results and the key membrane properties. • PVA membrane/20 wt % CS is the best for reversible chlor-alkali electrochemical cell. [ABSTRACT FROM AUTHOR]

In this work, hydrogen peroxide (H 2 O 2) is produced using an optimized electrochemical cell equipped with a gas diffusion electrode (GDE) as cathode, reaching efficiencies as high as 20.1%, when operating in a single compartment configuration, which increases up to the range 50–60, when a proton exchange membrane is used to separate the anodic and cathodic compartments, pointing out the great significance of the anodic oxidation of H 2 O 2 and the scavenging effects of the oxidants produced on the anode surface. As compared to previous materials tested, the GDE implemented in this cell underwent a more sustainable manufacturing procedure and exhibited an outstanding performance. The H 2 O 2 produced electrochemically is dosed to the real leachate of an industrial dump, strongly polluted with derivatives of lindane. This waste is associated to the operation of a large facility in the seventies and contains different isomers of hexachlorocyclohexane and other chlorinated hydrocarbons, produced during the ageing of the dump. Effects of the addition of iron (II) sulfate salts and irradiation of UVC were also evaluated. All electrochemically-assisted technologies evaluated (named as chemical (EACO), Fenton (EAFO), photolysis (EAPO) and photo-Fenton (EAPFO) oxidations) were able to successfully remove the pollutants, although with important differences in the efficiencies reached. Results demonstrate that EACO, that is, oxidation by molecular H 2 O 2 is the most effective treatment for the treatment of this type of wastes, pointing out that activation of H 2 O 2 to hydroxyl radicals, either by electrochemically assisted Fenton or photolysis is not positive for this waste. As well, among the different pollutants contained in the raw waste, removal of hexachlorocyclohexane (HCHs) and non-chlorinated volatile organic compounds (VOCs) stands out (both groups being the primary species contained in the wastes). These results are very important not only because of the outstanding productions of H 2 O 2 reached with the novel approach of electrochemical cell used, but also because of the implications of the mechanistic understanding of the attack of H 2 O 2 species in the design of a full-scale application to remediate this real important problem. [Display omitted] • Improved production of H 2 O 2 with a novel GDE and cell. • H 2 O 2 is produced with efficiencies over 20% in non-divided configurations. • Improved efficiency when using divided cells, with values as high as 50–60%. • Several electrochemical H 2 O 2 based technologies suitable for degradation wastes. • Unexpectedly H 2 O 2 more efficient that hydroxyl radicals in destroying CHCs. [ABSTRACT FROM AUTHOR]

• Electro-absorption assisted by ultrasound improves the treatment of gaseous streams polluted with BTX. • Ultrasound has a more positive effect on the electro-absorption at low values of current density. • Elimination rate increases as the current density increases. • Elimination efficiency (mmol A−1 L−1) and the synergy coefficient decreases when the current density increases. In this work, it is evaluated the influence of the application of ultrasound (US) on the absorption and electrochemically assisted absorption of gaseous streams polluted with benzene, toluene, and xylene (BTX). The experimental device combines a jet mixer absorber and a single-compartment electrochemical flow cell equipped with boron-doped diamond (BDD) anode. Results show that application of US has a positive effect on the amount of the pollutants absorbed and oxidized. This is explained in terms of the promotion in the mass transfer processes and because of the activation of oxidising species. Intermediates produced in the oxidative degradation of BTX were principally carboxylic acids. When current density increases, the removal rate increases. However, the elimination efficiency (mmol A−1 h−1) and the synergy coefficient decrease. A simple model is formulated and applied, and it reproduced satisfactorily experimental results and help to understand the processes involved. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Anode influences importantly on cathodic production of H 2 O 2. • In using DSA-Cl 2 , concentrations in the nearness of 4 g L−1 can be reached. • The lower concentrations with BDD are explained in terms of the production of predators. • A phenomenological model was proposed considering effect of predators. • The model explains clearly the reactivity and the influence of anodes. In this work, the electrosynthesis of hydrogen peroxide from the oxygen reduction reaction is evaluated using a flow-by electrochemical cell under different operation conditions and electrodes. In addition, a phenomenological model is proposed to understand the processes that occur inside the electrochemical reactor, and how the predatory species act against the production of H 2 O 2 at high concentrations. In comparing different types of anodes, the electrosynthesis of H 2 O 2 is almost twice as efficient when using DSA-Cl 2 instead of BDD as the anode, which allowed it to reach concentrations as high as 4.2 g L‾1. The rate of decomposition of H 2 O 2 is higher when the more vigorous anode is used. This decomposition is not only caused by the H 2 O 2 on the anode surface or by its self-decomposition within the bulk, but it is mostly related to the electrochemical processes of production of H 2 O 2 ′s predatory species such as ozone and peroxymonopersulfate. The formulated phenomenological model explains and satisfactorily reproduces the influence of anode type, electrolyte, and current density on the electrosynthesis of H 2 O 2 at high concentrations obtaining regression coefficients higher than 0.99. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integration of SERPIC-UCLM® cell and TMPr for phototreatment of RO C /NF C by SR-AOPs. • SERPIC-UCLM® cell presents enhanced mass transport compared to existing reactors. • PMSA self-decomposes at neutral pH of RO C /NF C into PMS. • PMS and PDS showed the same degradation patterns of CECs in RO C /NF C phototreatment. • 2.4 mM PMS increased the CECs degradation and ensured compliance with regulations. This study investigates the integration of an in-house 3D printed electrochemical cell − SERPIC-UCLM® cell – for the in situ generation of peroxymonosulfuric acid (PMSA) with a lab-scale tubular membrane photoreactor (TMPr) to evaluate the effectiveness of sulfate-radical advanced oxidation processes (SR-AOPs) in eliminating contaminants of emerging concern (CECs) from reverse osmosis and nanofiltration concentrates (RO C and NF C , respectively). First, the SERPIC-UCLM® cell was evaluated in terms of mass transport features employing the limiting current technique, demonstrating favorable volumetric mass transport rates (k m A ∼ 10–3 s–1) and Sherwood values (Sh > 300) under the laminar flow regime (110 < Reynolds (Re) < 790). Afterward, the effect of the electrolyte (sulfuric acid, H 2 SO 4) initial pH in the electrochemical generation of PMSA was studied, with an initial pH of 1 selected as optimal. PMSA is a highly reactive peroxyacid that undergoes self-decomposition at neutral pH media (e.g., RO C and NF C with a pH of 7.6 and 7.9, respectively), primarily existing in the form of peroxomonosulfate (PMS). Additionally, the phototreatment of the RO C and NF C was assessed using the electrogenerated PMS and commercial peroxydisulfate (PDS) under the same conditions. The results indicated comparable degradation patterns for CECs in both RO C and NF C. Furthermore, the application of 2.4 mM PMS resulted in removals higher than 60 % for 7 of the 11 CECs identified in the NF C , and ensured compliance with wastewater discharge regulations for pH, chemical oxygen demand (COD), and total suspended solids (TSS) levels. These findings emphasize the importance of this technology, showing its advantages in terms of versatility and logistics. [ABSTRACT FROM AUTHOR]

Water scarcity is becoming a serious threat for the implementation of energy storage devices based on hydrogen in the inland of dry regions, because of the difficulties in finding appropriate sources of water and the important environmental problem associated with the discharge of rejection saline streams produced during the purification of water. This becomes an opportunity for chloralkaline technology in which the quality of water used is lower than the required in other hydrogen production technologies. This work compares the performance of chloralkaline electrolyzers fed with different solutions of NaCl (from brackish water to brines) with that obtained feeding two natural water samples (seawater and porewater) and three processed waters (rejections streams of the electrodialysis, reverse osmosis of the porewater and a real rejection of the reverse osmosis of a vineyard). All tests were made with a lab-scale 3-D printed cell where, in addition, the performance of Ti/RuO 2 and Pb/PbO 2 anodes were compared, being always better the results obtained in the tests made with the Ti/RuO 2 electrode. Results obtained indicate that efficiencies reached using these alternative sources are lower than those which can be reached using synthetic brines that, in turn, were very near to the standards reached in the chloralkaline industry. In the case of hydrogen production, the maximum values were obtained for seawater, reaching efficiencies proximate to 8.0 mg H 2 (Wh)−1. Rejection streams of desalination processes were found to be less efficient, attaining values in the range 2 and 4 mg H 2 (Wh)−1. Regarding the production of chlorine and caustic soda, better performances were reached again with seawater (161.7 mg Cl 2 (Wh)−1 and 0.092 mg OH− (Wh)−1) and with the rejection of the electrodialysis, which also reached sound values of 90.4 mg Cl 2 (Wh)−1 and 0.107 mg OH− (Wh)−1. Results obtained are promising and indicate a path that must be further worked for the implementation of a greener water management strategy in the hydrogen -based energy storage technology. • Different types of water can be successfully used to fed chloralkaline electrolyzer. • Important influence of the composition & concentration and necessity of concentration. • Performance of electrolyzers with Ti/RuO 2 electrodes better than with Pb/PbO 2. • Electrolysis of seawater reaches 8 mg H 2 (Wh)−1,161.7 mg Cl 2 (Wh)−1 and 0.092 mg OH− (Wh)−1. • Among the concentration technologies, better results are reached by electrodialysis. • Necessity to improve performance of membranes against crossover of chlorine. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complete methodology for the manufacture of tailored electrochemical cells is described. • Conceptualization, chemical & mechanical design, fabrication, and testing as main stages required. • SWOT analysis based on electrochemical, chemical, mechanical, and economic issues. • Chemical and mechanical sizing successfully predicts performance during testing. • Testing needs for hydraulic, pneumatic, electric, and process evaluation. • Adaptation of weight-based cost-estimation procedures to new polymer-based prototypes. This work aims to become a methodological approach to the manufacturing of tailored electrochemical cells conceptualized for specific purposes, using the advantages provided by the 3-D printing technology. Through the complete evaluation of a case study, an electrochemically assisted absorption cell ready to remove VOCs, the different stages required to manufacture a prototype are completely addressed including the conceptualization, chemical and mechanical design, manufacturing, and testing of the printed cell. The main challenges tackled include conducting a SWOT analysis to select among different prototype concepts, chemical and mechanical calculations to properly size the device, selection of materials, and implementation of the engineering design into the constraints defined by the printing. Details about cost estimation are also provided by adapting the weight-based cost-estimation procedures used in mechanization companies to the evaluation of the cost of one of these new polymer-based prototypes in in-house applications and, even, to estimate which could be a realistic cost for potential industrial production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stacked cells in parallel configuration performs better than in series. • Increased electrode size cell performs better than stacking cells. • Successful scale up by a factor of 4 in the Caro's acid electrochemical production. • Successful resizing (enlarging) of a very efficient electrochemical prototype cell. • Important effect of scavengers suggested by a simple phenomenological model. This work focuses on very important aspects associated with the scale up of electrochemical devices by facing a 4-times increase in the electrochemical production of the Caro's acid, starting from a very efficient electrochemical cell that was developed and evaluated in previous works for this process. Thus, the effect is compared of (a) increasing the size of the electrodes by four by resizing, adapting, and manufacturing the cell prototype using 3-D printing technology and (b) that of stacking four cells to reach the same surface area, using different hydraulic connection configurations. Results demonstrate that the resizing of the electrochemical cell is more successful than stacking four cells. Resizing allows to obtain not only results that are comparable to those obtained by the lower scale cell but even to improve those results, because of the lower impact of edge effects. Regarding hydraulic connection, it was found that it is better to use parallel than series configuration. A simple phenomenological model is used to conclude that scavenging effects are higher when the series configuration is used. The resized cell was fully evaluated from the fluid dynamic behavior, pointing out its outstanding behavior. [ABSTRACT FROM AUTHOR]

Abstract: This work is focussed on the application of an electrochemical technology to regenerate the bonding agent of a polymer-supported ultrafiltration process, technique commonly used to remove metal ions from wastewaters. To do this, a batch rotating-electrode electrochemical cell has been set up to recover the copper bind to partially ethoxylated polyethyleneimine by electrodeposition. The influence of the main parameters (current efficiency, stirring rate, pH, electrode material and nature of the counterion) on the performance of the process has been studied. Current efficiency is clearly enhanced with the stirring rate, reaching values as high as 0.93 for the optimum working conditions. Regarding pH, this variable has been observed to play an important role in process efficiency. Thus, it has been found that the reactor can operate at pH 4 without affecting process performance. This is a clear advantage with respect to other regeneration techniques and also to previous works of electrochemical regeneration. The electrode material seems to have a clear influence on process behaviour and especially on the appearance of a first transitory stage with lower current efficiency. Finally, the electrolyte salt also influences significantly on the results and the presence of sulphate as counterion leads to the best system performance. [Copyright &y& Elsevier]

Abstract: In this work, it has been shown that the temperature (ranging from 100 to 175°C) greatly influences the performance of H3PO4-doped polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cells by several and complex processes. The temperature, by itself, increases H3PO4-doped PBI conductivity and enhances the electrodic reactions as it rises. Nevertheless, high temperatures reduce the level of hydration of the membrane, above 130–140°C accelerate the self-dehydration of H3PO4, and they may boost the process of catalyst particle agglomeration that takes place in strongly acidic H3PO4 medium (as checked by multi-cycling sweep voltammetry), reducing the overall electrochemical active surface. The first process seems to have a rapid response to changes in the temperature and controls the cell performance immediately after them. The second process seems to develop slower, and influences the cell performance in the “long-term”. The predominant processes, at each moment and temperature, determine the effect of the temperature on the cell performance, as potentiostatic curves display. “Long-term” polarization curves grow up to 150°C and decrease at 175°C. “Short-term” ones continuously increase as the temperature does after “conditioning” the cell at 125°C. On the contrary, when compared the polarization curves at 175°C a continuous decrease is observed with the “conditioning” temperature. A discussion of the observed trends is proposed in this work. [Copyright &y& Elsevier]

• It is possible to operate the chloralkali process with reversible electrochemical cells. • Performance of chloralkali PEM fuel cell is seriously affected by operation at high temperatures. • Maximum current and power densities of 12 mA cm−2 and 7 mW cm−2 are obtained at 20°C working in fuel cell mode. • Maximum current efficiency of chlorine production of 97.3% (1.82 mmol h−1 cm−2) is obtained operating in electrolyzer mode using an electrode of 25 cm2. This work demonstrates the viability of MEAs based on Nafion membranes for being used in reversible electrochemical cells for the chloralkali process. It also shows the effect of the operation temperature, from room temperature up to 80 °C, and humidification of the chlorine stream on the performance of these cells as fuel cell. Results demonstrate that these cells can be operated in reversible mode, yielding a current density of approximately12 mA cm−2 at a cell potential of 0.5 V, when operating as fuel cells fed with gaseous chlorine and hydrogen. The maximum power density achieved is 7.0 mW cm−2, which is much higher than that obtained with the same system fed with hydrogen and chlorine dissolved into liquid electrolytes. It is important to operate at room temperatures because efficiency decreases dramatically with temperature in an irreversible way, affecting the electrode. Humidification is necessary for the hydrogen stream and convenient for the chlorine stream, although it does not solve the irreversible cell damage caused by operation at high temperatures. Current efficiency of chlorine production is above 95 %, when operating as electrolyzer feeding a solution containing 2.0 M of NaCl. The rate of production of chlorine was 45.4 mmol h−1 at 100 mA cm−2 and the Cl 2 /O 2 molar ratio is 9.54, which is much higher than the values obtained in previous works which are between 3 and 5. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3-D Ti catalyst-less cathode is efficient for electrolytic production of H 2 O 2. • Successful operation in one/two compartments and continuous/batch configurations. • 3-D Ti coupling in a 3D-printed resin cell is highly efficient for G/L reactions. • Coulombic efficiencies of 69.72 % and energy consumption of 9 mg H 2 O 2 (Wh)-1. • Unexpected effect of the salt contained in the electrolyte. Hydrogen peroxide is produced efficiently in a catalyst-less electrochemical cell manufactured at lab scale (4 cm2 of electrode size) by resin and titanium 3-D printing. The electrolyte inlet and outlet of the cell are designed to promote a very turbulent flow pattern that provides good mixing of the liquid and gas phases and minimizes the mass transport limitations. The mechanization of the titanium contributes to an efficient gas diffusion in the cathode which was successfully adapted to the 3-D printed cell resulting in a very efficient gas–liquid reactive absorbent unit. The effect of the electrolyte, operation mode, gas and liquid flow rates were evaluated on the electrochemical production of hydrogen peroxide and the results obtained were successfully fitted to a simple phenomenological model that helped to obtain a deep understanding of the process. The proposed electrochemical gas–liquid absorber achieved coulombic efficiencies as high as 69.72 % and energy consumptions close to 9 mg H 2 O 2 (Wh)−1 when the system was operated in continuous mode with the most efficient conditions (no cell compartmentation and feeding pure oxygen with electrolytes containing sulphate salts at pH near 3). Those values of efficiencies are in the upper range of the results found in the literature for the electrochemical production of hydrogen peroxide, even though no catalytic coating was used to promote this cathodic reaction. An unexpected effect of the salt contained in the electrolyte was observed indicating the existence of other production mechanisms that require further characterization. [ABSTRACT FROM AUTHOR]

In this work, the disinfection of highly faecal-polluted surface water was studied using a new electrochemical cell (CabECO ® cell, manufactured by CONDIAS) specifically designed to produce ozone in water with very low conductivity. The disinfection tests were carried out in a discontinuous mode to evaluate the influence of the electrode current charge passed. The effect of the current density was also studied in order to optimize the disinfection conditions and to simultaneously prevent the formation of undesirable by-products (chlorates and perchlorates) during the electrolysis. The results demonstrate that this technology is robust and efficient, and it can suitably disinfect water. During electrolysis, the chloride contained in the water was oxidized to hypochlorite, and this compound was combined with ammonia to form chloramines. Both hypochlorite and chloramines (formed by the well-known break point reaction) promoted persistent disinfection and seemed to be mainly responsible for the disinfection attained during the electrochemical process. Chlorate and perchlorate could also be produced, although the low concentrations of chloride in the tested water made them irrelevant. The removal of the total organic carbon under the applied operating conditions was not very efficient (although it reached 50% in 2 h) and the production of trihalomethanes was very low, below 100 ppb for all tests. [ABSTRACT FROM AUTHOR]

• A novel integrated electro-absorption cell has been manufactured using 3-D printing. • Improved used of oxidants by preventing electrogenerated ozone wasting. • Gas-phase oxidants are generated and effectively used in the degradation of benzene. • Up to 60% of benzene degradation is achieved at 50 mA·cm−2. This work is focused on the evaluation of the performance of a novel integrated electrochemically assisted absorption reactor. This reactor combines a PEM cell (equipped with Nafion 117 membranes, boron doped diamond anode and titanium cathode) and a packed absorption column into a one compartment device that helps to maximize the use of electrogenerated oxidants by promoting the oxidation of gaseous pollutants. The device has been made using 3D printing technology with a clear Formlabs resin as printing material. Benzene was used as model of volatile organic compound (VOCs). Results demonstrate that this technology prevents wasting of ozone and obtains high efficiencies in the removal of benzene. As well, it is shed light on the mechanisms of benzene absorption and degradation in the liquid phase and on the effect of the current density on the efficiency of the process. Maximum removal efficiencies of nearly 60% are attained working at 50 mA·cm−2 with a moderate energy consumption. Lower degradation at higher current densities is explained in terms of the benzene desorption from liquid to gas phase provoked by the intense gas generation at the electrochemical cell (mainly H 2 and O 2). These results demonstrate the viability of this new reactor for the removal of VOC's. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • 3-D printing can be used to optimize the casing of PEM electrochemical cells. • Important role of scavengers in the electrochemical production of ozone. • Current density, electrolyte, and pressure effects are evaluated. • Good fluid dynamic needed to minimize O 3 - scavengers interactions. • Productions of ozone as large as 0.240 mg/(Ah cm2). • Coulombic current efficiencies as large as 5.9%. Ozone (O 3) is a powerful oxidant widely used in disinfection and wastewater treatment. In this work, a novel 3-D printed casing for electrochemical cells has been specially designed and manufactured for Proton-Exchange Membrane (PEM) electro-ozonizers, trying to promote an improved fluid dynamic including an efficient evacuation of gases produced during the electrolysis and aiming to minimize the interaction among ozone and scavengers. It is demonstrated that reaching high efficiencies in the electrochemical production of ozone is limited by the action of electrogenerated scavengers, among which cathodically formed hydrogen peroxide outstands. This explains the effects observed regarding current density (higher efficiencies at higher current densities applied, because hydrogen peroxide production is prevented), electrolyte composition (better efficiencies with lower concentrations of non-reacting electrolytes) and operation pressure (better results at lower pressures, because hydrogen peroxide formation depends more importantly on dissolved oxygen than ozone production). A very good performance is obtained, with ozone productions as high as 0.240 mg/(Ah cm2) and maximum current efficiencies of 5.9% under the best operation conditions (1.0 mM of HClO 4 , 330 mA/cm2 and 1 bar), which demonstrate the suitability of the technology tested and the good perspectives of 3D printing to improve performance of electrochemical processes. [ABSTRACT FROM AUTHOR]

H 2 S is a gaseous compound that contributes to air pollution. In this work, the electrochemical oxidation treatment of gaseous streams polluted with H 2 S is evaluated using a jet mixer and electrochemical cell device, in which the performance of electrolytic and electro-Fenton assisted absorption processes are compared. Results demonstrate the feasibility of both processes to remove H 2 S, reaching coulombic efficiencies of nearly 100% in the electrolytic assisted absorption, and 70–80% in the electro-Fenton assisted absorption. Aqueous solutions containing phosphate salts as electrolyte were found to be suitable as absorbents for the process. Efficiency in the cathodic production of H 2 O 2 in these solutions using the experimental device was found to be as high as 32.8% (1.184 mgH 2 O 2 /min) at 12 °C and atmospheric pressure. Sequential formation of SO 2 and SO 3 is obtained by the oxidation of H 2 S contained in the gas. These species are hydrolysed, and a part remained in the absorbent as SO 3 2− and SO 4 2−, while the rest is dragged in the outlet gas. SO 3 production is promoted by electrolytic assisted absorption and polysulphides by the electro-Fenton technology. Low concentrations of elemental sulphur are detected in the solid suspensions formed during the process. [Display omitted] • Elimination of H 2 S from gaseous streams by electrochemically assisted absorption. • Electrochemical production of H 2 O 2 with efficiency as high as 32.8%. • Coulombic efficiency of 100% in electrolytic absorption and 80% in electro-Fenton. • Electrolytic absorption produces mainly SO 3 and electro-Fenton, polysulphides. • Applying 0.3 A, removals rates of H 2 S as high as 1.827 mgS/min are obtained. [ABSTRACT FROM AUTHOR]

In this work, the disinfection of the effluent of the secondary treatment of a municipal wastewater treatment plant is studied using two stacks of commercial electrochemical cells powered with very low current densities (0.14–10 A m −2 ), in order to prevent the formation of chlorates and perchlorates during the electrolysis. Results demonstrate that this technology is robust and efficient and it can attain the complete disinfection of wastewater even at very low current densities. These low current densities are high enough to produce hypochlorite and chloramines (when ammonium is present in solution), being the disinfection process more efficient when the concentration of chloramines is higher. Therefore, the presence of hypochlorite together with higher concentrations of chloramines significantly improve the removal of microorganisms. In comparing the two stacks studied in this work, it was obtained that commercial DiaCell stacks containing bipolar connected electrodes are more efficient than those containing monopolar-connected electrodes for the disinfection. Differences are explained in terms of the higher cell voltage applied in that stack (higher current density in bipolar stack) that results in (1) an improved reduction of nitrates to ammonium (BDD cathode in bipolar stack) with the latter formation of chloramines as the main positive effect and (2) in the increase in the power consumed as the primary negative consequence. [ABSTRACT FROM AUTHOR]

• Efficient mineralization of the VOCs contained in the air using electro-scrubbing technology. • Benzoquinone and carboxylic acids are formed in the absorbent but not found in the outlet stream. • Percentage of benzene gaseous removal increases by increasing operation current density. • Mass transport control of the electrochemical degradation of benzene into the absorbent/electrolyte. This paper is focused on the evaluation of the electrochemically assisted absorption process (electro-absorption) as a treatment for volatile organic compounds contained in polluted air flows. Benzene degradation was used to test the technology, using a system consisting of a packed absorption column and a single compartment electrochemical cell equipped with boron-doped diamond (BDD) as anode and steel-steal as cathode. The influence of inlet gas flow rate and operation current intensity was evaluated by monitoring the concentration of benzene and intermediates both, in the liquid absorbent / electrolyte and in the outlet gaseous stream. Results show that steady-state values reached, during benzene absorption and electro-absorption, increase when the inlet gas flow rises from 1.5 to 6.0 L h−1 and that the bare absorption process retains benzene only up to this steady-state value of the liquid and then, it has no effect on the removal of benzene. Concentrations of benzene in the absorbent/electrolyte decreases with the increase in the current density during electrochemically assisted processes. As well, mineralization was found to be very important, as expected because of the very low concentrations of benzene into the liquid and the very high efficiencies of the electrolytic degradation with BDD electrodes, and benzoquinone and carboxylic acids were identified as the primary intermediates. These species were not detected in the outlet gas flow. The decrease in the concentration and mass flow of benzene in the outlet streams confirms that electro-absorption is a functional electrochemical application to remove benzene from gaseous streams. When current density rises (10, 50 and 100 mA cm−2), the degradation percentage increases. The values obtained were 43, 61 and 75% with 1,5 L h−1 of inlet gas flow and 10, 25 and 37 % with 6 L h−1. However, the degradation percentage relative to the energy consumption decreases when the current density rises. Results were, correspondingly, 24.7, 4.2 and 2.2 % kWh−1 with 1,5 L h−1 of inlet gas flow and 7.1, 2.1 and 1.4 % with 6 L h−1. This energy efficiency trend was explained because mass transport becomes the bottleneck in the oxidation of diluted organic solutions. These results contribute to expand the understanding of the mechanisms involved in the electro-absorption of benzene and recommend for further research in the topic, due to the relevance of the treatment results. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • DSA® and BDD were very efficient in removing VOCs from aqueous medium. • In methanol solutions, BDD promotes greater conversion of VOCs than DSA®. • Value-added products were produced in methanol medium. • The new concept of electro-refinery was explored. In the search for a method that can remove pollutants from gases or enhance the efficiency of the treatment of liquid wastes, electrolysis of water and methanol solutions containing benzene, toluene, and xylene were carried out in this work. Using a filter-press flow electrochemical cell, the efficiency of two different anodes (diamond coatings and mixed metal oxides) were evaluated against the electrochemical oxidation of contaminants in the different solvents mentioned. Results demonstrate that these pollutants can be removed from both types of matrixes and that the nature of the electrode influences greatly on the efficiency. In aqueous medium both electrodes perform similarly but diamond overcomes metal oxide anodes in methanol. In addition to a higher mineralization rate in that case, several highly value-added products are obtained during the process. For instance, anisole, methyl anisole and dimethyl anisole were produced from electrochemical oxidation of benzene, toluene and xylene, respectively, in methanol medium. These results pointing out that a change in the paradigm of the treatment must be made in the next years, going from the destruction of the pollutants to their conversion into highly valuable products at the frame of the circular economy premises. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a novel integrated electrochemical process for urban wastewater regeneration is described. The electrochemical cell consists in a Boron Doped Diamond (BDD) or a Dimensionally Stable Anode (DSA) as anode, a Stainless Steel (SS) as cathode and a perforated aluminum plate, which behaves as bipolar electrode, between anode and cathode. Thus, in this cell, it is possible to carry out, at the same time, two different electrochemical processes: electrodisinfection (ED) and electrocoagulation (EC). The treatment of urban wastewater with different anodes and different operating conditions is studied. First of all, in order to check the process performance, experiments with synthetic wastewaters were carried out, showing that it is possible to achieve a 100% of turbidity removal by the electrodissolution of the bipolar electrode. Next, the effect of the current density and the anode material are studied during the ED–EC process of actual effluents. Results show that it is possible to remove Escherichia coli and turbidity simultaneously of an actual effluent from a WasteWater Treatment Facility (WWTF). The use of BDD anodes allows to remove the E. coli completely at an applied electric charge of 0.0077 A h dm−3 when working with a current density of 6.65 A m−2. On the other hand, with DSA anodes, the current density necessary to achieve the total removal of E. coli is higher (11.12 A m−2) than that required with BDD anodes. Finally, the influence of cell flow path and flow rate have been studied. Results show that the performance of the process strongly depends on the characteristics of the initial effluent (E. coli concentration and Cl−/NH4 + initial ratio) and that a cell configuration cathode (inlet)–anode (outlet) and a higher flow rate enhance the removal of the turbidity from the treated effluent. [Copyright &y& Elsevier]

Abstract: In this work, the effect of the cathode material (conductive diamond, stainless steel, silicon carbide, graphite or lead) and the current density (150–1400Am−2) on the removal of nitrates from aqueous solutions is studied by electrolysis in non-divided electrochemical cells equipped with conductive diamond anodes, using sodium sulphate as the electrolyte. The results show that the cathode material very strongly influences both the process performance and the product distribution. The main products obtained are gaseous nitrogen (NO, N2O and NO2) and ammonium ions. Nitrate removal follows first order kinetics, which indicates that the electrolysis process is controlled by mass transfer. Furthermore, the stainless steel and graphite cathodes show a great selectivity towards the production of ammonium ions, whereas the silicon carbide cathode leads to the highest formation of gaseous nitrogen, which production is promoted at low current densities. [Copyright &y& Elsevier]

[Display omitted] • Hydrogen peroxide electrogeneration was boosted with the application of pressure. • Clofibric acid abatement was significantly enhanced with pressurized electro-Fenton. • Specific energy consumption was reduced when working above atmospheric pressure. • Pressure did not affect leaching nor damaged the heterogeneous catalyst. • Mathematical modelling based on experimental data represented the system behavior. In this research, a bench-scale installation was tested for the heterogeneous electro-Fenton treatment of clofibric acid. The setup consists of a pressurized flow-through electrochemical cell equipped with a catalyst fluidized-bed and aerated with a jet mixer. The novelty of the research is two-fold: the use of the pressurized-jet aerator on an electro-Fenton treatment is tested and it is one of the first studies combining pressure with heterogeneous catalysis in electro-Fenton. Moderate relative pressures, up to 2 bar, were analyzed. Initially, the electrogeneration of hydrogen peroxide was tested, showing that it is remarkably boosted by the application of pressure. Then, the elimination of clofibric acid by means of an electro-Fenton treatment was carried out at 0.12 and 0.25 A, using iron-containing alginate beads as the catalyst. Regardless of the current intensity, the increase from atmospheric pressure to 1 gauge bar boosted the elimination of the pollutant and reduced the specific energy consumption of the electrochemical cell. Specifically, at 0.25 A an abatement higher than 98% was achieved in 8 h at atmospheric pressure while only 1 h was required at 1 bar of gauge pressure. However, a further increase of the pressure to 2 bar did not report a major improvement. Moreover, the effect of pressure on the catalyst was analyzed, concluding that the integrity of the alginate beads was not compromised by pressure. In fact, the iron leaching was very similar at 0, 1 and 2 bar: around 30% after 8 h of treatment. Finally, a mathematical model was developed, using the experimental data to obtain the necessary fitting parameters, which allowed to understand better the behavior of the bench-scale reaction system. [ABSTRACT FROM AUTHOR]

• MMO-3D made by microwaves are highly efficient for removing pollutants hold in urine. • The configuration of the MF-Reactor favors the degradation of antibiotics from urine. • PhEC with MMO shows the greatest reduction in antibiotic activity of MRP, PENG, CLP. This work focuses on the importance of choosing a suitable electrochemical cell to remove antibiotics from urines. For this purpose, we investigate the use of two electrochemical cells for electrolysis and photo-electrolysis of urine polluted with a mixture of Penicillin G, Meropenem, and Chloramphenicol. The two reactors studied were a conventional flow pass electrochemical cell (E-cell) and a microfluidic flow-through reactor (MF-Reactor). Both reactors are equipped with a mixed metal oxide anode (MMO-RuO 2 IrO 2) produced by hybrid heating using microwaves. The MMO coating was deposited on a Ti plate for the E-cell (2-D electrode) and on a Ti foam for the MF-Reactor (3-D electrode). Results demonstrate that the MF-Reactor stands out to reduce two important factors in electrochemical oxidation, the ohmic resistance associated with the microfluidic concept and the mass transfer limitations associated with the flow-through configuration. Moreover, it allows operating at a lower effective current density because of its larger active anodic surface area. Photo-electrolysis results in faster removal of all antibiotics studied in the MF-Reactor and E-cell, compared to the single electrolysis, thereby highlighting the significance of UV light-mediated electrochemical oxidation processes. This work highlights that despite the large number of papers focused on the selection of suitable electrodes for the electrochemical treatment of different types of wastes, the choice of the electrochemical cell can be even more important than the selection of those electrode materials, and it demonstrates that even using the same coating as the anode, highly different outcomes can be reached. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical design of the cell as a key issue in the scale-up. • Successful scaling-up of the heterogeneous electro-Fenton process. • Clofibric acid abatement was achieved regardless of the cell. • Higher hydrogen peroxide production & clofibric acid removal with improved design. With the aim of bringing the heterogeneous electro-Fenton (EF) treatment one step closer to a more realistic operation, the scaling-up of that technology was evaluated. Assays were performed firstly at lab scale in a stirred-tank reactor and then at bench scale in a flow setup including a jet aerator and a microfluidic flow-through electrochemical cell. A fluidized-bed reactor was added to the bench-scale installation in order to retain the solid catalyst, iron-containing alginate beads. To the best of the authors' knowledge, there are no precedent studies reporting a heterogeneous EF treatment in a similar bench scale-configuration. Hydrogen peroxide generation and clofibric acid removal were assessed at both scales at current intensities of 0.12 and 0.25 A. Results showed that the scaled-up treatment was more efficient and cost-effective: at bench scale 18 times more volume was treated, the mass production of hydrogen peroxide was 28 higher and the specific cost for the removal of clofibric acid was cut by more than half. The most efficient treatment turned out to be the EF performed at 0.12 A at bench scale. Those results highlighted the importance of the reactor design in the scaling-up process. Additionally, aromatic intermediates were detected by liquid chromatography-mass spectrometry (LC-MS) and a degradation route was suggested. Carboxylic acids were also measured by HPLC confirming that the pollutant is mineralizing. [ABSTRACT FROM AUTHOR]