Cathode Compartment Research Articles

Ammonia-selective recovery from anaerobic digestate using electrochemical ammonia stripping combined with electrodialysis

An electrodialysis (ED)-electrochemical ammonia stripping (EAS) hybrid process is used for the quick and efficient recovery of ammonia from anaerobic digestate. A series of EAS experiments using synthetic ammonia solutions was conducted to determine the optimal operating conditions for the ED-EAS hybrid process with actual anaerobic digestate. These parameters included the feeding modes (anodic vs. cathodic), applied currents, anolyte composition, and capture chemicals, with a focus on their impact on ammonia recovery. As a result, cathodic feeding showed advantages over anodic feeding because of its benefit in converting NH4+ to NH3 through successful pH elevation in the cathode compartment. High current density provided sufficient OH− to increase the cathode compartment's pH, and using Na2HPO4, a salt of triprotic acid, as an anolyte resulted in a rapid pH increase due to pH buffering, resulting in a better ammonia recovery. Through three cycles of ED operation (8 h), the ED-EAS hybrid process experiment for actual anaerobic digestate concentrated ammonia to 3.775 g/L, three times higher than the initial concentration. Ammonia was recovered to 90.5 ± 0.4 % with 11.6 kWh/kg-NH3 energy consumption from the ED concentrate in 5 h using the EAS. This study demonstrated the possibility of ammonia-selective recovery from anaerobic digestate using an integrated ED-EAS system.

Selective electrochemical methanation of carbon dioxide using a sulphide derived CuZn catalyst

Efficient catalysts facilitate the electrochemical reduction of CO2, enabling its conversion into fuels or chemical feedstocks through proton coupled electron transfer processes. Among these catalysts, Cu-based ones stand out for their unique ability to produce hydrocarbon products with high faradaic efficiencies. This study focuses on the use of sulphide-derived (SD)-CuxZny nanoparticle catalysts, which have been found to exhibit enhanced methane selectivity during CO2 reduction in an H-Cell with 0.10 M KHCO3 as the electrolyte. The composition of the catalysts plays a crucial role in determining their catalytic behavior. At an optimal Cu/Zn ratio of 1:1, the SD-CuZn catalyst demonstrates exceptional methane production, achieving a faradaic efficiency of 76 ± 3 % at a potential of −0.98 V vs RHE. Moreover, a partial current density of −4.5 mA cm−2 was achieved at a more negative potential of −1.09 V vs RHE. Ex situ characterization highlighted the significance of partially reduced CuS species in influencing the selectivity of hydrogenated carbon products. When CO2 reduction was performed in a flow cell equipped with a gas diffusion electrode with 1.0 M KHCO3 or 1.0 M KOH electrolytes in both anodic and cathodic compartments, the current density increased due to the enhanced mass transport rate. However, the altered conditions lead to a shift in selectivity, favoring carbon monoxide over methane. It is important to note that insights garnered from H-Cell experiments may not be directly extrapolated to flow cell setups.

Evolution of the Bromate Electrolyte Composition in the Course of Its Electroreduction inside a Membrane-Electrode Assembly with a Proton-Exchange Membrane.

The passage of cathodic current through the acidized aqueous bromate solution (catholyte) leads to a negative shift of the average oxidation degree of Br atoms. It means a distribution of Br-containing species in various oxidation states between -1 and +5, which are mutually transformed via numerous protonation/deprotonation, chemical, and redox/electrochemical steps. This process is also accompanied by the change in the proton (H+) concentration, both due to the participation of H+ ions in these steps and due to the H+ flux through the cation-exchange membrane separating the cathodic and anodic compartments. Variations of the composition of the catholyte concentrations of all these components has been analyzed for various initial concentrations of sulfuric acid, cA0 (0.015-0.3 M), and two values of the total concentrations of Br atoms inside the system, ctot (0.1 or 1.0 M of Br atoms), as functions of the average Br-atom oxidation degree, x, under the condition of the thermodynamic equilibrium of the above transformations. It is shown that during the exhaustion of the redox capacity of the catholyte (x pass from 5 to -1), the pH value passes through a maximum. Its height and the corresponding average oxidation state of bromine atoms depend on the initial bromate/acid ratio. The constructed algorithm can be used to select the initial acid content in the bromate catholyte, which is optimal from the point of view of preventing the formation of liquid bromine at the maximum content of electroactive compounds.

Degradation of real lindane wastes using advanced oxidation technologies based on electrogenerated hydrogen peroxide

In this work, hydrogen peroxide (H2O2) 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 H2O2 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 H2O2 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 H2O2 is the most effective treatment for the treatment of this type of wastes, pointing out that activation of H2O2 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 H2O2 reached with the novel approach of electrochemical cell used, but also because of the implications of the mechanistic understanding of the attack of H2O2 species in the design of a full-scale application to remediate this real important problem.

Electrophoretic Deposition of Poly(ethylene oxide) Gel-Polymer Electrolyte for 3D NiO/Ni Foam Anode Based Lithium-Ion Batteries

The goal to further increase energy and power density of conventional 2D structured lithium-ion batteries is driving research towards more complex 3D batteries with large surface area and accordingly high active material mass loading. So far, many attempts have been implemented to prepare 3D structured LIBs. However, the hindrance of the realization comes with removing the separator which requires conformally and homogeneously coating the scaffolded areas of the electrode. The conformal coating of polymer electrolyte without any defects on the surface of the electrode is one of the most essential and challenging problems to solve to avoid the short circuit between the anode and cathode compartments of the 3D LIBs. In this paper, electrophoretic deposition technique was successfully used for the first time to coat the 3D NiO on the nickel foam anode with polyethylene oxide (PEO) gel-polymer electrolyte. The resulting polymer electrolyte was thin and uniform with the thickness range of 2.5–3.0 μm. The developed NiO@Ni foam anode coated by PEO gel-polymer electrolyte exhibited outstanding cycling stability of 100 cycles at 0.1 C rate, delivering a capacity of 406 mAh g−1. This simple coating approach allowed a cell operation at room temperature without a commercial separator, which is an excellent result for further developing high-energy-density 3D batteries.

Solid Oxide Electrochemical Cells for Nitrogen and Oxygen Production

This work presents an efficient electrochemical process for N2 and O2 production based on a solid oxide electrochemical cell technology by oxygen extraction from air. Cells with a 53×53 mm2 size consist of ca.10 μm CGO electrolyte sandwiched between composite electrodes made from either LSCF-CGO, or LSF-CGO were produced by a conventional tape casting method. To boost performance at low temperature, the electrodes were infiltrated with Pr-oxide. The electrochemical performance of the cells were characterized by iV and EIS at different temperatures with air used as feed stock to the cathode compartment and air, or oxygen used as sweep gas to the anode compartment. A voltage below 200mV is achieved to drive a current of 1A/cm2 through the cell, which can provide a purity of 90% of N2 at 650 °C. The cells were demonstrated to operate for producing a >98% pure N2 stream without degradation over a 1500h period at cell voltages below 255mV.

Cathode Materials for Microbial Fuel Cells

The most important problems of today are meeting the increasing energy needs and avoiding environmental pollution caused by fossil resources usage for energy production. In addition, the decrease in usable water in the world has become a threat to human health and the population. Microbial fuel cells (MFC) have become more interesting in recent years because of their potential to solve these three important problems. Organic and inorganic contents in wastewater can be seen as potential energy sources. MFCs are the only systems that can convert the chemical energy in the organic and inorganic content of wastewater into electricity. While this transformation is realized, the process of cleaning the wastewater can be done. Reducing the costs of these systems is the most important parameter to accelerate the use of the system. In particular, studies on reducing the cost and increasing the efficiency of the catalysts used in the cathode compartment where the oxygen reduction reaction takes place are predominant. In this study, cathode materials used in MFCs will be examined and alternative materials will be discussed.

Sustainable integrated process for cogeneration of oxidants for VOCs removal

This study upgrades the sustainability of environmental electrochemical technologies with a novel approach consisting of the in-situ cogeneration and use of two important oxidants, hydrogen peroxide (H2O2) and Caro's acid (H2SO5), manufactured with the same innovative cell. This reactor was equipped with a gas diffusion electrode (GDE) to generate cathodically H2O2, from oxygen reduction reaction, a boron doped diamond (BDD) electrode to obtain H2SO5, via anodic oxidation of dilute sulfuric acid, and a proton exchange membrane to separate the anodic and the cathodic compartment, preventing the scavenging effect of the interaction of oxidants. A special design of the inlet helps this cell to reach simultaneous efficiencies as high as 99% for H2O2 formation and 19.7% for Caro's acid formation, which means that the cogeneration reaches efficiencies over 100% in the uses of electric current to produce oxidants. The two oxidants' streams produced were used with different configurations for the degradation of three volatile organic compounds (benzene, toluene, and xylene) in a batch reactor equipped with a UVC-lamp. Among different alternatives studied, the combination H2SO5/H2O2 under UVC irradiation showed the best results in terms of degradation efficiency, demonstrating important synergisms as compared to the bare technologies.

NiO & CuO nanocomposites coated photoanode for conversion of CO2 into solar fuel using photoelectrochemical cell

ABSTRACT Photoelectrocatalytic reduction of carbon dioxide to solar fuel exists as a novel approach for addressing energy demand, and environmental concerns due to high efficiency and less energy requirement as compared to other technology. The predominant goal of the current work is to investigate the impact of metal oxide (NiO & CuO) supported photoanodes for enhancing CO2 conversion into solar fuel using a photoelectrochemical cell (PEC). The photoanodes were incorporated with rGO with combinations of metal oxide nanocomposites and coated on the electrode surface. The PEC consists of anode and cathode compartments divided by proton exchange membrane, the anode and cathode are filled with 0.1 M KOH and 0.5 M KCl respectively. The xenon arc lamp (100W) is used as a light source and carbon dioxide is supplied with a flow rate of 10 mL/min. The synthesized nanoparticles were characterized using XRD, FTIR, and Cyclic Voltammetry. The experimental results showed that the NiO-coated photoanode observed the better performance than CuO coated electrode and it had achieved the maximum solar fuel (Formic Acid) production rate of 9.223 μmol/hr/cm2 with a Faradic efficiency of 14.83% as compared to the control electrode.

Recent Advances in the Development of Sustainable Composite Materials used as Membranes in Microbial Fuel Cells.

MFC can have dual functions; they can generate electricity from industrial and domestic effluents while purifying wastewater. Most MFC designs comprise a membrane which physically separates the cathode and anode compartments while keeping them electrically connected, playing a significant role in its efficiency. Popular commercial membranes such as Nafion, Hyflon and Zifron have excellent ionic conductivity, but have several drawbacks, mainly their prohibitive cost and non-biodegradability, preventing the large-scale application of MFC. Fabrication of composite materials that can function better at a much lower cost while also being environment-friendly has been the endeavor of few researchers over the past years. The current review aims to apprise readers of the latest trends of the past decade in fabricating composite membranes (CM) for MFC. For emphasis on environmental-friendly CM, the review begins with biopolymers, moving on to the carbon-polymer, polymer-polymer, and metal-polymer CM. Lastly, critical analysis towards technology-oriented propositions and realistic future directives in terms of strengths, weakness, opportunities, challenges (SWOC analysis) of the application of CM in MFC have been discussed for their possible large-scale use. The focus of this review is the development of hybrid materials as membranes for fuel cells, while underscoring the need for environment-friendly composites and processes.

Electrochemical Production of Formate Directly from Amine-Based CO2 Capture Media

Introduction There is an urgency for the development and establishment of technologies to deal with the effects of climate change and increasing temperature of the planet.1 The decrease in the CO2 emissions is a possible path, and the capture of CO2 from the atmosphere is another alternative to try and tackle the effects of climate change.2 The combination of capture and conversion of CO2 is a potential approach to achieve the net-zero emission goals and a circular economy for the future.3 Amine scrubbing is an industrially established capture technology that utilizes mainly monoethanolamine (MEA) as the capture solution to capture CO2 from post-combustion flue gases. The process has the disadvantage of a high energy demand, which prevents its wider application.2 This study proposes a novel capture and utilization (CCU) combination: the use of the MEA capture solution as electrolyte for the electrochemical CO2 reduction (eCO2R). In that way, the CO2 capture and conversion will be combined in the same medium, avoiding the energy-intensive regeneration step, thus saving energy, as well as generating products of industrial interest. Sn-based catalysts were primarily chosen due to their selectivity towards formate, one of the most straightforward reduction products from CO2. Results The eCO2R from the capture media (30 wt% MEA solutions, saturated with CO2) was promoted in a zero-gap type reactor, composed of an Sn-based cathode, a Ni foam anode and a bipolar membrane (BPM) separating the cathode and anode compartments. The BPM is responsible for providing protons to the cathode side of the electrolyzer, which promote the hydrolysis of the carbamate on the surface of the catalyst and thus enhances the CO2 availability and consequently the eCO2R. Figure 1 presents a scheme of the zero-gap electrolyzer, highlighting the hydrolysis of the carbamate in contact with the catalyst, and compares the faradaic efficiencies (FE) towards formate obtained by different setups of the zero-gap electrolyzer, at -50 mA cm-2.The Sn nanoparticle (SnNP)-based catalysts show a low efficiency for the eCO2R from the capture media (up to 5%). As published in the literature, surfactants are capable to inhibit the hydrogen evolution reaction (HER) in electrochemical systems and thus promote the eCO2R.4 The surfactant cetyltrimethylammonium bromide (CTAB) was therefore added to the system and the FE towards formate increased, although merely up to 6.43%. To further increase the surface area available for the eCO2R, a metal gauze was introduced as support for the working electrode (WE). Here, a Cu gauze with electrodeposited Sn (SnED) was used as WE and the obtained FE was 70% higher than for the carbon supported SnNP catalysts, up to 8.49%, without the addition of the surfactant. The hydrophilic nature of the metal surface (in comparison to the carbon paper substrate of the NPs) and a bigger surface area could be the reasons behind this enhancement in the FE using metal WE. Future studies will focus on the further enhancement of the FE towards formate. Conclusion This study shows the feasibility of a novel CCU technology: the electrochemical reduction of CO2 to formate from an amine-based capture medium. Sn-based catalysts lead to an FE of up to 8.49%. The use of a metallic electrode lead to a larger enhancement of the FE, in comparison to the addition of a surfactant to the electrolyte for the SnNP-based catalyst. There is yet room for further improvement of the faradaic efficiency by the combination of the metal electrode and the use of surfactants to inhibit the HER, as well as the use of catalysts with higher selectivity towards the product, such as Bi. The use of a zero-gap electrolyzer shows the feasibility of scaling up the system to industrially relevant dimensions and the easiness of incorporating the electrochemical system to the end of pre-existing capture plants. References Ghiat, I., & Al-Ansari, T. (2021). Journal of CO2 Utilization, 45.Gutiérrez-Sánchez, O., Bohlen, B., et al. (2022). ChemElectroChem, 9(5), e202101540.Li, M., Irtem, E., et al. (2022). Nature Communications 2022 13:1, 13(1), 1–11.Chen, L., Li, F., et al. (2017). ChemSusChem, 10(20), 4109–4118. Figure 1

Continuous Electrolysis of Carbon Dioxide for the Production of Formate with High Efficiency

Carbon dioxide capture, storage, and utilization is nowadays considered one of the most interesting approaches to reduce emissions to the atmosphere and, therefore, to mitigate climate change. In this sense, the electrochemical reduction of carbon dioxide to value-added products is gaining attention, since it permits storing excess of energy from renewable and intermittent sources (e.g. solar or wind), in the form of chemicals [1]. Among the reaction products, both formic acid and formate are products of great interest that could be obtained by this process, due to its use as raw materials in several industries and its promising use as a reactant in low-temperature fuel cells and as a renewable hydrogen carrier molecule. Although there is a large number of studies published in literature focusing on the electrocatalytic reduction of carbon dioxide to formic acid and formate[2], few of them achieve relevant trade-offs among the figures of merit typically used to analyze the performance of the process, like (i) the concentration of formate, (ii) the Faradaic Efficiency towards the reaction products, (iii) the energy consumption per kmol of formate and (iv) the current density supplied to the electrochemical reactor.In this context, this communication aims at studying the continuous electrolysis of carbon dioxide, operating with a single pass of the reactants through the electrochemical reactor and using Bi-carbon supported electrocatalysts, to obtain formate with high energy efficiency. In this sense, the electrocatalysts are deposited by air-brushing techniques in the form of a membrane electrode assembly in the cathodic compartment of the electrochemical reactor. This configuration permits direct contact between the Gas Diffusion Electrode and the Nafion cationic exchange membrane which acts as a separator between both compartments of the electrochemical filter press reactor [3].The influence of some key variables is rigorously studied, such as (i) the amount of water in the carbon dioxide input stream, (ii) the current density and (iii) the Bi catalyst loading deposited over the cathode. Firstly, the performance of the electrocatalytic reduction of carbon dioxide to formate employing a Bi catalyst loading of 0.75 mg·cm-2 in terms of i) formate concentration, ii) Faradaic Efficiency towards formate and iii) energy consumption per kmol of formate are assessed as a function of the current density and the water flow in the carbon dioxide input stream. In this point, it is important to remark that, working with an industrially-relevant current density of 200 mA·cm-2 and with a water flow of 0.5 g·h-1, high formateconcentrations of up to 312 g·L-1 were obtained with Faradaic Efficiency towards formateof 25 %, respectively. Consequently, additional tests are performed with a Bi loading in the cathode of the electrochemical filter press of 1.5 mg·cm-2. Combinations of relevant values of concentrations, Faradaic Efficiency for formate and energy consumption of 337 g·L-1, 89 %, and 180 kWh·kmol-1, respectively, are achieved with a current density of 45 mA·cm-2 and with a water flow of 2 g·h-1. These results are one of the best trade-offs reported in the field of carbon dioxide electroreduction to formic acid or formate among these figures of merit, thus achieving a significant advance in this field. However, there are many challenges to be addressed for the implementation of the process at an industrial scale, and therefore, more research focused on the advanced electrocatalytic materials, innovative electrode configuration, and improved electrochemical reactors are still required.

Experimental investigation of hydrogen production performance of various salts with a chlor-alkali method

In this experimental study, the hydrogen production performance of aqueous solutions of NaCl, KCl, and CaCl2 salts via an electrochemical method through a chlor-alkali reactor is investigated. For this purpose, a laboratory-scale reactor consisting of anode and cathode compartments is built. The compartments of the reactor are separated by a cation exchange membrane which prevents the mixing of anolyte and catholyte solutions and also allows positive ions (Na+, K+, and Ca2+) and some water to pass through. Electrodes made of 316 stainless steel are used in the compartments of the reactor due to their economic efficiency. While the anode compartment of the reactor is fed with the aqueous solutions of NaCl, KCl, and CaCl2 salts one by one, the cathode compartment is fed with one of the diluted aqueous solutions of NaOH, KOH, and Ca(OH)2 bases depending on the type of salt used. Experiments are carried out at three different cell voltages (3, 4, and 5 V) and three different cell temperatures (30, 50, and 70 °C), and five different electrolyte flows (0.4, 0.6, 0.8, 1.0, and 1.2 g/s). Since the reactor dimensions are very small, experiments are also carried out with small changes in the electrolyte mass flow rate. It is observed that active chlorine gas causes serious contamination in the anode compartment and erosion on the electrode in this compartment. Therefore, the expected chlorine gas output from the anode compartment of the reactor is not observed. Luckily, a significant amount of hydrogen gas output is observed from the cathode compartment of the reactor. The minimum hydrogen production rate is 37.23 mL/h when the aqueous solution of CaCl2 is used with a mass flow rate of 0.4 g/s and cell voltage of 3 V at the cell temperature of 30 °C. The maximum hydrogen production rate is 437.72 mL/h when KCl salt solution is used with a mass flow rate of 1.2 g/s and cell voltage of 5 V at the cell temperature of 70 °C.

Electrochemical oxidation of a real effluent using selective cathodic and anodic strategies to simultaneously produce high value-added compounds: Green hydrogen and carboxylic acids

In this work, the simultaneous production of green hydrogen (H2) and carboxylic acids from the electrochemical treatment of washing machine effluent is demonstrated for the first time. The electrochemical treatment of the effluent was carried out using a solar-powered polymer electrolyte membrane (PEM-type) cell with a boron-doped diamond (BDD) electrode as anode and a Ni-Fe-based SS (stainless steel) mesh as the cathode with two types of electrolytes (0.1 mol/L H2SO4 and 0.1 mol/L Na2SO4), by applying different current densities (j). A synthetic and non-destructive effluent transformation strategy was implemented by controlling the operating conditions in order to regulate precursor-intermediates, oxidants, and •OH production. The results show the formation of high value-added products (carboxylic acids) and energy sources (green H2) in the anodic and cathodic compartments, respectively, with the possibility of selective electroconversion to acetic acid depending on the electrolyte and j. The green H2 production rate is also influenced by the pH conditions, the electrolyte, and the anodic j. The technology proposed here may constitute a promising, efficient and sustainable route towards the United Nations’ Sustainable Development Goals (SDGs) 6 and 7.

Targeted electro-redox facilitating efficient delithiation of lithium manganese ion-sieve selective electrode

The electrically switched ion exchange (ESIX), as the most promising technique for the efficient extraction of lithium from brine, especially the lithium manganese ion-sieve membrane electrode, possesses the advantages of high selectivity, high adsorption capacity, and high stability. And to enable the simultaneous lithium intercalation and de-intercalation at the cathode and anode, respectively, the selective electrode ought to be delithiated before use. Traditional chemical and electrochemical delithiation and electrochemical techniques consume enormous amounts of reagents and energy, respectively. Thermodynamics and electrochemical analysis indicated that the cathodic reaction induced the high cell voltage, which in turn caused the emitting of toxic gases and high energy consumption. Thus, in this study, a targeted-redox system was adopted to alleviate the above problems. By adding excessive Cu2+ into the cathode compartment, the cell voltages in 5 h reduced from 3 V to about 1.5 V and further reduced to 1.2 V if diluted HCl was also added. With lower cell voltage and higher current density, a higher delithiation rate can be reached (95.83 %). Furthermore, Cu2+ can be regenerated by bubbling O2 under an acidic atmosphere, which enables the re-utilization of the cathodic solution. The targeted electro-redox system can reduce 2980.49 J of the energy consumption compared with the current electrochemical delithiation method, meanwhile, the utilization of cheaper counter electrode makes it economically viable.

Selective butyric acid production from CO2 and its upgrade to butanol in microbial electrosynthesis cells

Microbial electrosynthesis (MES) is a promising carbon utilization technology, but the low-value products (i.e., acetate or methane) and the high electric power demand hinder its industrial adoption. In this study, electrically efficient MES cells with a low ohmic resistance of 15.7 mΩ m2 were operated galvanostatically in fed-batch mode, alternating periods of high CO2 and H2 availability. This promoted acetic acid and ethanol production, ultimately triggering selective (78% on a carbon basis) butyric acid production via chain elongation. An average production rate of 14.5 g m−2 d−1 was obtained at an applied current of 1.0 or 1.5 mA cm−2, being Megasphaera sp. the key chain elongating player. Inoculating a second cell with the catholyte containing the enriched community resulted in butyric acid production at the same rate as the previous cell, but the lag phase was reduced by 82%. Furthermore, interrupting the CO2 feeding and setting a constant pH2 of 1.7–1.8 atm in the cathode compartment triggered solventogenic butanol production at a pH below 4.8. The efficient cell design resulted in average cell voltages of 2.6–2.8 V and a remarkably low electric energy requirement of 34.6 kWhel kg−1 of butyric acid produced, despite coulombic efficiencies being restricted to 45% due to the cross-over of O2 and H2 through the membrane. In conclusion, this study revealed the optimal operating conditions to achieve energy-efficient butyric acid production from CO2 and suggested a strategy to further upgrade it to valuable butanol.

LITHIUM HYDROXIDE FORMATION BY MEMBRANE ELECTROLYSIS

The production of high-purity lithium hydroxide (LiOH) solution by electrochemical conversion of soluble lithium salts (membrane electrolysis) was tested on semi-industrial scale. Stainless steel (cathode) and lead (anode) were used as electrode materials. Lithium sulphate solution was utilised as anolyte and water - as catholyte. During membrane electrolysis, water oxidation takes place in the anode compartment with the formation of gaseous oxygen and protons. Lithium ions permeate through the cationic membrane into the cathode compartment, where gaseous hydrogen and hydroxide ions are formed as the products of water decomposition on the cathode, so lithium hydroxide gets concentrated up to 33-36 g/dm3 with respect to lithium oxide. Electrolysis efficiency is 50-55 % for one process cycle. Sulphuric acid formed in the anode compartment may be then neutralised by adding lithium carbonate, and the formed lithium sulphate may be re-used in membrane electrolysis, which means anolyte recycling. Five successive electrolysis cycles with recycled anolyte allow an increase in the degree of lithium ion transfer from the anode to cathode compartment to 95-98 %. It is established that, in addition to lithium, other metal ions (sodium, potassium, calcium, etc.) and sulphate ions migrate through the cation-exchange membrane into the cathode compartment from anolyte solution. To evaluate the quality of the obtained lithium hydroxide monohydrate (LiOH•H2O), lithium hydroxide solutions obtained both by membrane electrolysis and by the traditional lime causticisation process were evaporated. Comparison between the concentrations of impurity ions in lithium hydroxide monohydrate samples obtained using different methods shows that the product of better purity may be synthesized from lithium sulphate solution by membrane electrolysis.

Photoelectrochemical Production of Hydrogen Peroxide with TiO2 and 1,5-Di(thien-2-yl)-9,10-anthraquinone via a Selective Two-Electron Oxygen Reduction Reaction in the Two-Compartment Cell

The industrial process of hydrogen peroxide (H2O2) synthesis proceeds through the hydrogenation of anthraquinone followed by successive oxidation in an organic solvent. This process is a multistep synthesis that is far away from green synthesis. An alternative photoelectrochemical (PEC) H2O2 production method requires only sunlight and water. Herein, we established the direct production of H2O2 by using a two-compartment PEC cell composed of TiO2 nanorods hydrothermally grown on fluorine-doped tin oxide as a photoanode for water oxidation and 1,5-di(thien-2-yl)-9,10-anthraquinone (AQTh) anchored carbon cloth as a cathode for the selective two-electron (2e–) reduction of oxygen. This photoanode and cathode are positioned in an anodic compartment and a cathodic compartment of a two-compartment cell, respectively. The Nafion membrane (N-117) separates these two compartments. This PEC cell continuously produces H2O2 at −0.1 VRHE applied voltage, which reaches 60 μM after 3 h. The density functional theory study is carried out to better understand the H2O2 production mechanism and the role of thiophene substituents on anthraquinone.

A Short Review: Comparison of Zinc–Manganese Dioxide Batteries with Different pH Aqueous Electrolytes

As the world moves towards sustainable and renewable energy sources, there is a need for reliable energy storage systems. A good candidate for such an application could be to improve secondary aqueous zinc–manganese dioxide (Zn-MnO2) batteries. For this reason, different aqueous Zn-MnO2 battery technologies are discussed in this short review, focusing on how electrolytes with different pH affect the battery. Improvements and achievements in alkaline aqueous Zn-MnO2 batteries the recent years have been briefly reviewed. Additionally, mild to acidic aqueous electrolyte employment in Zn-MnO2 batteries has been described, acknowledging their potential success, as such a battery design can increase the potential by up to 2 V. However, we have also recognized a novel battery electrolyte type that could increase even more scientific interest in aqueous Zn-MnO2 batteries. Consisting of an alkaline electrolyte in the anode compartment and an acidic electrolyte in the cathode compartment, this dual (amphoteric) electrolyte system permits the extension of the battery cell potential above 2 V without water decomposition. In addition, papers describing pH immobilization in aqueous zinc–manganese compound batteries and the achieved results are reported and discussed.

Photoelectrocatalytic Surfactant Pollutant Degradation and Simultaneous Green Hydrogen Generation.

For the first time, we demonstrate a photoelectrocatalysis technique for simultaneous surfactant pollutant degradation and green hydrogen generation using mesoporous WO3/BiVO4 photoanode under simulated sunlight irradiation. The materials properties such as morphology, crystallite structure, chemical environment, optical absorbance, and bandgap energy of the WO3/BiVO4 films are examined and discussed. We have tested the anionic type (sodium 2-naphthalenesulfonate (S2NS)) and cationic type surfactants (benzyl alkyl dimethylammonium compounds (BAC-C12)) as model pollutants. A complete removal of S2NS and BAC-C12 surfactants at 60 and 90 min, respectively, by applying 1.75 V applied potential vs RHE to the circuit, under 1 sun was achieved. An interesting competitive phenomenon for photohole utilization was observed between surfactants and adsorbed water. This led to the formation of H2O2 from water alongside surfactant degradation (anode) and hydrogen evolution (cathode). No byproducts were observed after the direct photohole mediated degradation of surfactants, implying its advantage over other AOPs and biological processes. In the cathode compartment, 82.51 μmol/cm2 and 71.81 μmol/cm2 of hydrogen gas were generated during the BAC-C12 and S2NS surfactant degradation process, respectively, at 1.75 V RHE applied potential.