1,721,006 research outputs found
Electrochemical Advanced Oxidation Process: from conventional system to solid polymer electrolyte system
No full textAmong old materials and different approaches to enhance stability and electrochemical activity of solid oxide cells
No full textPerovskite materials are widely studied as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFC) for their relevant properties regarding electrocatalytic activity or stability. Nevertheless, a material that combines both it is not yet available. Among them, La1-XSrxMnO3 (LSM), La1-xSrxCo1-yFeyO3 (LSCF), Ba1-xSrxCo1-yFeyO3 (BSCF), La1-xSrxFeO3 (LSF), La1-xBaxCoO3 (LBC), were deeply investigated but their properties are not completely exploited or optimized.
The study starts from LSM – based electrodes, which show a change in kinetic mechanism over a overpotential threshold. These results [1,2] open new horizons about the employment of this material, up today considered not suitable for IT-SOFC temperature range. A first application, with promising results, is proposed here with a LSM infiltration in LSCF and BSCF scaffold [3].
Promising results are obtained also by mixing BSCF and LSCF powders [4]. Three different BSCF:LSCF ratio are considered to produce three different cathodes. All the new compositions show an improvement of activity for oxygen reduction reaction, with very competitive values of polarization resistance. Moreover, one of these new electrodes has also a lowering of degradation rate compared with reference materials
In the last year of this project, other two materials are combined and their interactions investigate. LSF, providing a high stability, is coupled with LBC, which has a really high surface electrocatalytic activity. The two materials are tested in different thin film systems. When they are mixed before the sintering stage react forming a new perovskite phase (Ba0.099Sr0.297La0.594Fe0.8Co0.2O3), with a higher activity. The reaction is avoided producing a bilayer system, and the presence of LBC top layer over a LSF dense thin film drastically reduces polarization resistance, highlighting promising results.
Moreover a particular attention has been paid to deeper integrate different approach to analyze electrochemical impedance spectroscopy results, such as equivalent circuit modeling, distribution of relaxation time and physically based model [5]
Electro-Fenton, solar photoelectro-Fenton and UVA photoelectro-Fenton: Degradation of Erythrosine B dye solution
No full textThe treatment of Erythrosine B, selected as a model compound, has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) such as electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Experiments are performed in a one-compartment cell with a BDD anode, and a commercial carbon felt cathode at pH = 3, treating a volume of 0.3 L in each test. The irradiation plays a crucial role in the increasing of hydroxyl radical production and in the recover of iron catalyst. A faster colour and COD removal degradation are achieved under the light application. UVA photoelectro-Fenton and solar photoelectro-Fenton processes allow degrading COD entirely in 90 min, while a conventional electro-Fenton does not reach 90% COD removal after 2 h. Energy consumptions are a substantial factor in process selection. Photo electro-Fenton with a UVA-100 W lamp has one of the best removal performance, but it becomes not suitable for application due to high energy demand, up to 515.6 kWh m−3, and the UVA system requires the main fraction of this energy. Possible alternatives are proposed to contain costs: the first is the reduction of UVA lamp power to 25 W, maintaining a high-performance removal with an Ec decreasing to 187.9 kWh m−3. Nevertheless, the lowest and competitive energy demands is obtained working with a solar photoelectro-Fenton system, where energy consumption are only related to the electrochemical process (20.9 kWh m−3), and removal is complete
Solid polymer electrolyte as an alternative approach for the electrochemical removal of herbicide from groundwater
No full textGroundwater represents one of the primary freshwater sources, but their pollution is rapidly increasing, and the development of tailored processes is mandatory. In this scenario, electrochemical advanced oxidation processes (EAOPs) represent a promising alternative to face this issue. Their application to groundwater is limited by low electrical conductivity, which directly affects cell voltage and then operating costs. In this paper, three different approaches to overcome this constrain are compared using a BDD anode and a Ti/RuO2 cathode. The first is the addition of a supporting electrolyte as sodium sulfate (Na2SO4); despite its efficacy to increase conductivity, some new problems are introduced in water source management and treatment plant for the electrolyte removal. An alternative approach is the reduction of gap-electrode from 5 mm up to some microns, equivalent to the thickness of a plastic mesh, used to avoid electrodes short-circuit. The third innovative method proposed here is the substitution of insulated mesh with an ionic conductor layer, a solid polymer electrolyte (SPE), like Nafion®117 sandwiched between the electrodes. This modification allows increasing electrochemical performance such as herbicide and COD removal, preserving energy consumptions. Moreover, SPE does not show any performance deterioration in the first 30 h of utilisation. The results suggest that the usage of SPE can be a promising approach for the treatment of groundwater
Electrochemical oxidation of organic pollutants in low conductive solutions
No full textThis mini-review supplies current opinion about the most recent works, which have been carried out toward the electrochemical treatment of organic compounds spike in low conductive solution. In particular, the first section is focused on the use of a solid polymer electrolyte in order to allow current flux with a low cell voltage even in a solution without supporting electrolyte. Meanwhile, the second section describes the microfluidic cells that are characterized by very small distances between electrodes (tens or few hundreds μm) that reduce the ohmic resistances and increase the mass transport of the pollutants to electrodes’ surfaces
Past and present of electrochemical treatment of organic pollutants
No full textOxidative electrochemical technologies offer an alternative solution to many environmental problems in the process industry, because electrons provide a versatile, efficient, cost-effective, easily automatable, and clean reagent. In electro-oxidation, organic pollutants can be removed by different methods:
(i) Direct electrolysis: the pollutants (R) are oxidized after adsorption on the anode surface without the involvement of any substance other than electrons:
Rads → Pads + ze-
(ii) Oxidation via intermediates of oxygen evolution: organic compounds are oxidised near the anode surface (M) at high potentials in the region of water discharge due to the participation of intermediates of oxygen evolution:
M + H2O → M(•OH) + H+ + e-
R + M(•OH) → M + CO2 + H2O
Anodes with high oxygen evolution overpotential, such as SnO2, PbO2 or boron-doped diamond (BDD) are ideal electrodes for the complete oxidation of organics to CO2 in wastewater treatment.
(iii) Indirect electrolysis mediated by oxidizing agents generated anodically: organic pollutants are removed through the mediation of some electroactive species generated at the anode surface, which act as intermediaries for electrons shuttling between the electrode and the organic compounds. The main oxidizing chemicals electrogenerated anodically are active chlorine and persulfates, that are produced by the oxidation of chloride and sulphates ions commonly present in wastewaters:
2Cl- → Cl2 + 2e-
2SO42- → S2O82- + 2H+ + 2e-
(iv) Electro-Fenton processes: the pollutants are removed by the •OH produced in the bulk of the solution using the electrogenerated Fenton's reagent where H2O2 is supplied in situ from the two-electron reduction of O2 on cathodes such as gas diffusion electrodes (GDE), reticulated vitreous carbon (RVC) or graphite-felt, and Fe2+ is continually regenerated from Fe3+ reduction:
Fe2+ + H2O2 → Fe3+ + OH- + •OH
O2 + 2H+ + 2e- → H2O2
Fe3+ + e- → Fe2+
(v) Coupled anodic and cathodic Processes: using an undivided cell, the contaminants are treated by H2O2 generated on the cathode and oxidizing agents or •OH generated at the anode.
Process selection depends on the nature of the electrode material, experimental conditions, and electrolyte composition. This lecture focuses on recent progress in the most promising electrochemical tools for the treatment of wastewater contaminated by organic pollutants
Application of boron-doped diamond electrodes for electrochemical oxidation of real wastewaters
No full textRecently, the synthesis of boron-doped diamond electrodes on different substrates and shapes have reached a promising development stage. Now, these electrodes can also be effectively used to destroy toxic or biorefractory organics in real effluents, such as municipal wastewaters effluents, hospital wastewaters, groundwater, petrochemical effluent, wastewaters from agri-food activities, and so on. The results of this mini-review show that BDD is effectively even for such real effluents, allowing the removal of pollutants under several different conditions. Nevertheless, further efforts are necessary to reach a wider market; in particular, the next stages must face the optimization of cell design and the integration of the electrochemical system with other water treatment and renewable energy sources
A kinetic study on oxygen redox reaction of a double-perovskite reversible oxygen electrode-Part I: Experimental analysis
No full textThe carbon-free energy transition requires the spread of advanced technologies based on high-performing materials. In this framework and particularly referring to electrochemical energy converting systems, double perovskites are arousing more and more interest as mixed ionic electronic conductors with flexible manufacturing, appropriate tailoring for many tasks and high chemical stability. Among their possible applications, they form excellent oxygen electrodes in solid oxide cell technology used as fuel cells, steam/CO2 electrolysis cells and electrochemical air separation units. In view of the encouraging results shown by SmBa1-x Ca x Co2O5+delta co-doped double perovskite, this research work aims at a detailed analysis of SmBa0.8Ca0.2Co2O5+delta performance and the identification of kinetic paths for oxygen reduction and oxidation reactions. The electrochemical characterization was performed over a wide range of operation conditions to evaluate the electrode reversible behaviour and the interplay of the recognized phenomena governing the overall electrode kinetics
La1-xSrxMnO3-δ, La1-xSrxCo1-yFeyO3-δ, Ba1-xSrxCo1-yFeyO3-δ; the Huey, Dewy and Louie of Solid Oxide Fuel Cell cathode materials
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