Flow-through Electrolyzer Research Articles

Energy consumption model of flow-through electrolyzer considering mass transfer overpotential for hydrogen production from alkaline water splitting

Flow-through electrolyzer can improve the efficiency of hydrogen production from alkaline water splitting and determining the optimal electrolyte velocity through electrode pores is crucial for reducing energy consumption. In this study, an energy consumption model of flow-through electrolyzer considering mass transfer overpotential (Emass) has been developed. The model of Emass due to gas hold-up (ϕ) in the electrolyzer accounts for the density, viscosity, surface tension, linear velocity, and current density. The model-predicted value is in good agreement with the experimental results, which indicated that the increase of velocity effectively reduces ϕ and Emass. Then, Voltage-Current curve models combining reversible voltage, activation overpotential, ohmic overpotential, and Emass are developed. Based on this, an energy consumption model, combining both consumption from electrolyzer and pumps, is established to evaluate the overall energy consumption of hydrogen production. It can be calculated the Emass at 400 mA cm−2, 6 M KOH, 353 K can be reduced from 0.363 V to 0.048 V if the circulation velocity rises from 0.001 m s−1 to 0.1 m s−1. The model predicts that total energy consumption is 4.36 kWh Nm−3 with energy consumption for pump being 0.02 kWh Nm−3 at 400 mA cm−2 and 0.063 m s−1.

Microporous structure flowing integrated with electrolytic water splitting based on stacked mesh electrode for hydrogen production

In order to promote gas bubble transport during water splitting for hydrogen production, stacked mesh electrodes integrated microporous structure flowing and electrolytic water splitting have been fabricated by electrodepositing CoFe alloy. The average size of the bubble on the mesh electrode surface is 40 μm and the release time of trapped bubbles in the pores of the electrode is 2.11 s during the process of water splitting at 50 mA cm−2 and 1 M KOH. The electrodes show excellent performance in both hydrogen evolution reaction (HER, 247 mV at 1000 mA cm−2) and oxygen evolution reaction (OER, 350 mV at 1000 mA cm−2). The required cell voltage at 1000 mA cm−2 for flow-through electrolyzer assembled with the stacked mesh electrodes is only 2 V under the condition of 6 M KOH, and 343 K. The voltage caused by the bubble in the flow-through electrolyzer assembled with stacked mesh electrodes is just about 50 mV at the current density of 1000 mA cm−2. The energy required for hydrogen production is only 4.04 kWh Nm−3 and 4.78 kWh Nm−3 under the current density of 200 mA cm−2 and 1000 mA cm−2, respectively. Besides, the flow-through electrolyzer assembled with the stacked mesh electrodes shows excellent stability with only a 60 mV increase in cell voltage after continuing electrolytic water splitting for 100 h at 1000 mA cm−2.

Production Tests of the Don Water Purification and Disinfection Technology

One of the promising ways to reduce the content of organic pollutants in natural waters is the use of biological processes in combination with sorption on powdered activated carbon followed by membrane filtration and, as the final stage, disinfection of the obtained permeate by direct electrolysis. The paper presents the results of the efficiency of purification of the Don water, which underwent physicochemical treatment from halogen-organic contaminants in a biosorption-membrane reactor and the dependencies characterizing the disinfection of water by direct electrolysis in a flow-through membraneless electrolyzer. The studies were carried out using powdered active carbon, hollow fiber, and flat plate membranes. An oxide iridium-ruthenium titanium anode (OIRTA) was used as electrodes in a flow-through electrolyzer. As a result of processing the experimental results, the efficiency of removing not only the turbidity and color of water, but also organic substances, which cause high permanganate oxidizability and COD, has been established. The results of experimental studies have shown a high efficiency of purification and disinfection of natural water to the requirements of SanPiN. The efficiency of COD reduction was on average 41.2%, color - 57.3%, permanganate oxidizability - 33.3%.

Incineration of the antibiotic chloramphenicol by electro-peroxone using a smart electrolyzer that produces H2O2 through electrolytic O2

The experimental characterization of the electro-peroxone (E-peroxone) process during the elimination of the antibiotic chloramphenicol (CAP) was carried out in a flow plant using a novel flow-through electrolyzer equipped with two anodes and two cathodes in a cascade configuration, anode-cathode-anode-cathode. The H2O2 is formed at the graphite felt cathodes by reducing O2 provided from the oxygen evolution reaction (OER) performed at the Ti|IrO2-Ta2O5 anodes. This electrolyzer avoids employing an air compressor to supply the O2 for the electrosynthesis of H2O2 during the E-peroxone process. The characterization of E-peroxone was performed by using 2 L of a solution containing 0.05 M Na2SO4 at concentrations of CAP from 20 to 50 mg L−1 TOC (48.9–122.3 mg L−1 CAP), studying the influence of pH (3–9), applied current density (5 ≤ j ≤ 15 mA cm−2), and solution flow rate (0.4 ≤ Q ≤ 1.0 L min−1) on the oxidation of CAP. The best performance reached 100% CAP degradation, 63% TOC removal, at pH 3, j = 10 mA cm−2, Q = 0.4 L min−1 and FO3=17.5 mg min−1. The mineralization current efficiency (MCE) and electrolytic energy consumption (EC) were 19% and 0.202 kWh (g TOC)−1, respectively. The comparison of E-peroxone with anodic oxidation aided by H2O2 (AO-H2O2) and ozonation showed the oxidative power sequence E-peroxone > ozonation > AO-H2O2. The evolution of carboxylic acids and inorganic ions was performed by chromatographic and spectrophotometric techniques. Finally, a route of CAP degradation is proposed.

Preventive Improvement of Wastewater Treatment Efficiency

This paper focuses on studying the effect of electrolytic water on wastewater decontamination processes, using model solutions and wastewater from the food-processing plant. The aqueous solutions under study were obtained by changing the redox potential (ORP), and pH of ordinary tap water using a pH corrector, which is a flow-through electrolyzer with a membrane separating the cathode and anode zones, and the solutions were obtained by adding to tap water a solution containing products of electrokinetic synthesis. Parameters that changed as a result of the study: ORP, TDS, pH. Solutions capable of almost complete inhibition of the vital activity and growth of microorganisms were obtained. Also, solutions were obtained that promoted their development, and when seeding them on a dense nutrient medium, there was continuous growth. Further research is advisable to detail the technical and economic indicators of water supply and sewerage schemes of municipal and industrial facilities with preventive water treatment processes.

Calcium-iron-D-gluconate complexes for the indirect cathodic reduction of indigo in denim dyeing: A greener alternative to non-regenerable chemicals

With an annual production of approximately 7–10 billion m2 the manufacturing of indigo dyed denim takes a substantial share in global textile production. At present the vast majority of dyeing processes with indigo still bases on the use sodium dithionite as reducing agent. For a successful replacement of the non-regenerable reducing agent by electrochemical processes, a combination of a regenerable redox system with an appropriate cell design is required. In the presented study, the use of embroidered electrodes in an 85 mA flow-through electrolyser for electrochemical indigo reduction has been investigated for the first time. Indirect cathodic reduction of indigo was achieved with use of a 0.1 M solution of a binuclear complex of calcium and iron with D-gluconate as a ligand. The electrochemically reduced indigo was then used in lab scale dyeing (1–3.5 g L−1 indigo), and the results were compared to reference dyeing experiments with sodium dithionite as reducing agent, by measuring the colour strength and CIElab colour coordinates. Comparison of the electrochemical technique for indigo reduction with the dithionite-based standard process indicates substantial potential for an improvement of the ecological profile of the dyeing process used at present. The electrical power demand for a full scale electrolyser is estimated to be in the range of 2.8–6.9 kW, leading to an energy consumption of 58–145 kWh d−1 as compared to a sodium dithionite consumption of 50–126 kg d−1. Introduction of biobased and regenerable chemical systems instead of non regenerable chemicals in indigo dyeing offers significant potential for reduction of the chemical load released into wastewater. A reduction of the sulphate concentration in the wastewater from the current values of 640–1600 mg L−1 to values well below the legal limit of 200 mg L−1 sulphate will be possible. By reuse of the washing water and the reversible reducing agent, a reduction of both water consumption (by 80%) and chemical consumption (by 50%) are expected.

Alkaline Water Electrolysis at 20 a cm-2 with a Microfibrous, Flow-through Electrolyzer

Improving both the efficiency and productivity of water electrolysis is necessary for making the electrochemical generation of hydrogen economically competitive. Flow-through electrodes are widely used to improve the efficiency and productivity of electrochemical processes, but studies of their use in alkaline water electrolysis are relatively rare. This work aimed to (1) test the hypothesis that the use of a flow-through electrode could enhance the rate of bubble removal from the electrode surface, thereby improving productivity, and (2) determine what length scale of electrode would maximize the surface area available for electrolysis without hindering bubble removal. To determine how the efficiency and productivity of the flow-through electrode depends on the electrode length scale, the performance of the oxygen evolution reaction was compared with flow-through electrodes consisting of a Ni foam, Ni microfibers (Ni MFs, d = 1.2 mm), and Ni-coated Cu nanowires (NiCu NWs, d = 350 nm). Although the turnover frequency (TOF) for the Ni foam was 2.4 times higher than the Ni MF electrode and 42 times higher than the NiCu NW electrode, its surface area was more than 90 times lower than the other electrodes, resulting in the lowest overall current density. Although the NiCu NW electrode had a higher surface area than the Ni MF electrode, it had a lower overall current density because of its low TOF. We attribute the high performance of the Ni MF electrode to the fact that the mean pore size of the Ni MF electrode (5-10 mm) is on the order of the mean bubble size (20 mm) that was measured by examining the bubbles generated from a mesh electrode. The performance of the Ni MF electrode was further improved by coating it with a Ni-Fe layered double hydroxide (LDH) catalyst, resulting in an OER overpotential of 247 mV at 0.1 A cm-2 and a Tafel slope of 26 mV dec-1. These values are among the lowest reported for Ni-Fe LDH catalysts. A Ni MF anode was paired with a Pt-coated Ni MF cathode to measure the overall productivity for water splitting. The maximum current density for water splitting was 20 A cm-2 at 3.9 V in 30% KOH, which is 20 times greater than the highest current densities previously reported for alkaline water electrolysis. This current density and voltage could be sustained for at least 8 hours with no signs of degradation. This high current density was attributed to the ability of the flowing fluid to promote bubble removal and keep the hot electrode surface from boiling water. This work demonstrates that flow-through microfibrous electrodes can improve the efficiency and productivity of alkaline water electrolysis. Figure 1

Towards the scale up of a pressurized-jet microfluidic flow-through reactor for cost-effective electro-generation of H2O2

The performance of a novel pressurized-jet microfluidic flow-through electrolyzer for the production of aqueous solution of H2O2 is assessed in this work. The reactor design is based on three aspects i) minimizing ohmic drops, by reducing the interelectrode gap to 150 μm and the use of a Duocel® aluminum foam as cathodic support; ii) maximizing mass transport, due to the use of three-dimensional electrodes fed in flow-through and iii) optimizing the aeration system coupling a pressurized circuit and a jet aerator. Results show that H2O2 can be produced with an instantaneous current efficiency of ≅ 100% up to 20 mA cm−3 and a corresponding production rate of 13.1 mg H2O2 h−1 cm−3 in a cathode of 16.5 cm3. Low ohmic resistances were measured even in low-conductive electrolytes, as for example 6 Ω in 0.0035 M Na2SO4 (0.7 mS cm−1). The electrical energy consumption of 3.65 kWh kg H2O2−1 at 10 mA cm−3 in 0.05 M Na2SO4 is the lowest reported so far in neutral-acid medium, confirming the cost-effectiveness of the system. A preliminary scale-up by increasing the cathode volume three times (up to 49.5 cm3) allowed the production rate to be multiplied by the same factor and confirms that the system is scalable. Theoretical calculations suggest that the cathode could be expanded up to 3600 cm3 (1 m thickness) under those aeration conditions (6 bar and 160 dm3 h−1 recirculation flow).

Optimization of the cathode material for nitrate removal by a paired electrolysis process

Ni, Cu, Cu 90Ni 10 and Cu 70Ni 30 were evaluated as cathode materials for the conversion of nitrate to nitrogen by a paired electrolysis process using an undivided flow-through electrolyzer. Firstly, corrosion measurements revealed that Ni and Cu 70Ni 30 electrodes have a much better corrosion resistance than Cu and Cu 90Ni 10 in the presence of chloride, nitrate and ammonia. Secondly, nitrate electroreduction experiments showed that the cupro-nickel electrodes are the most efficient for reducing nitrate to ammonia with a selectivity of 100%. Finally, paired electrolysis experiments confirmed the efficiency of Cu 70Ni 30 and Cu 90Ni 10 cathodes for the conversion of nitrate to nitrogen. During a typical electrolysis, the concentration of nitrate varied from 620 ppm to less than 50 ppm NO 3 − with an N 2 selectivity of 100% and a mean energy consumption of 20 kWh/kg NO 3 − (compared to ∼35 and ∼220 kWh/kg NO 3 − with Cu and Ni cathodes, respectively).

Softening of calcium-hydrocarbonate water in a flow-through electrolyzer with a filtrating cartridge

We have studied the impact of the amount of passed electricity and concentration of hydrocarbonate ions on the degree of softening calcium-hydrocarbonate water in a successive flow-through electrolyzer with a filtrating cartridge. It has been found that indispensable conditions for the softening of water containing 10 mg-eq/dm3 of calcium ions is the presence in it of hydrocarbonate ions (5–7 mg-eq/dm3) and treatment of water by electricity (300–450 C/dm3).

Electrochemical oxidation of phenolic compounds using a flow-through electrolyser with porous solid electrodes

Organic compounds such as phenol and cresols may be found in industrial wastewater along with other organics and are difficult to be economically removed down to concentrations below environmentally permissible limits. By circulating a wastewater through an electrolytic reactor with a stack of porous solid anodes and cathodes, it has been demonstrated that it is feasible to electrochemically oxidize phenolic compounds in the presence of other organic molecules. A porous solid DSA®-type titanium anode coated with several mixed oxide layers was used as the active material. At low applied current densities, phenol and cresol concentrations were reduced from 5000 ppb to below 20 ppb. The influence of the flow rate and electrodes number was also studied and it was demonstrated that the current density was the main factor to be considered. This work confirms the hypotheses of other authors on the reaction mechanisms involved during the electrochemical oxidation of cresol and phenol.

Synthesis of Dispersed System (CuO, ZnO) from Lump Braze with a Vertical Flow-through Electrolyzer

The electrochemical synthesis of a mixture of dispersed oxides (CuO and ZnO) from secondary lump braze was studied. The influence exerted by electrolysis parameters on the intensity of synthesis of the oxide mixture was investigated. The design of the electrolyzer and the flow diagram for synthesis of a mixture of oxides (CuO and ZnO) from lump braze was suggested.

Dynamics of Changes in the Anionic Composition of Sodium Chloride Solutions in a Flow-through Electrolyzer

Products theoretically obtainable by electrochemical treatment of sodium chloride solutions in the dynamic mode are considered. Hydrated chlorine, and hypochlorous and hydrochloric acids are determined quantitatively by iodometric titration, spectrophotometry, and potentiometry. A comparative analysis is made of theoretical and experimental results obtained in determining chlorine-containing ions.

Electrochemical removal of nitrate ions in waste solutions after regeneration of ion exchange columns

Electrochemical reduction of nitrate ions in synthetic regenerating solutions after ion exchange column regeneration was studied. The influence of current density on the current efficiency was determined in the range 2.8–7.6 mA cm−2 in a diaphragmless flow-through electrolyser in a batch recirculation mode. A Cu cathode and a Ti/Pt anode was used, the temperature being maintained at 25 ∘C. Highest integral current efficiency occurred at 2.8 mA cm−2. The presence of about 6 mg dm−3 Cu ions in treated solution was found to prevent a decrease in cathode activity and, consequently, in electrolysis efficiency. The catalytic influence of Cu ions was verified by potentiodynamic polarisation experiments on a copper rotating disc electrode and by chronopotentiometry performed during the course of electrolysis.

Cathodic reduction of hypochlorite during reduction of dilute sodium chloride solution

Sodium chloride solutions of concentration 15 and 30 g dm−3 were electrolysed in a flow-through electrolyser with a titanium/TiO)2/RuO2 anode at current densities 1059–4237 A m−2. The current yield for the reduction of hypochlorite on a stainless steel cathode was found to be 13–32% at 7 g dm−3 NaClO, in agreement with that calculated on the basis of the Stephan-Vogt theory. Migration of ions was taken into account, the diameter of hydrogen bubbles was set equal to 0.04 mm and the coverage of the electrode with the bubbles was estimated as ϑ = 0.897. The results of calculations show that the reduction rate of hypochlorite at low NaCl concentrations is lowered by migration. Literature data for the reduction of hypochlorite are in accord with the current yield calculated on the basis of the Stephan-Vogt theory using ϑ = 0.787 and ϑ = 0.949.