Dual solution-type HCHO fuel cell systems using an anion exchange resin membrane with electroless-plated Cu or Pd anode

Loading characteristics of a prototype HCHO fuel cell systems with an anion exchange membrane which separates the anolyte from the catholyte were investigated. Electrodes of Cu or Pd, deposited by an electroless-plating technique onto the membrane, showed high electrocatalytic activity to the anodic oxidation of HCHO in 1 M NaOH solution. The system with Cu anode and 1 M NaOH for both anolyte and catholyte showed high loading characteristics but poor durability, whereas that with 1 M K₂CO₃ showed low characteristics because of lowered pH of the anolyte. It was shown that a dual solution-type cell with 1 M K₂CO₃ anolyte and 1 M NaOH catholyte yielded improved characteristics as compared with the simple K₂CO₃ system. The output level was, however, at an unsatisfactory level owing to poor membrane conductance. The temperature dependence of the output performance was studied in the range 7–55°C.     

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm, was used as the separator between the two chambers of the cell. The trickle bed electrode of dimensions 0.23 m high ×0.0362 m wide × 0.003 m thick was used on the cathode side. The anolyte chamber of the cell, 0.23 m high × 0.0362 m, wide × 0.003 m thick was operated at a fixed anolyte flow of 2.0 × 10^–6 m³ s^–1 while the oxygen loadings in the trickle bed was kept constant at 0.102 kg m^–2 s^–1. Other operating conditions include inlet and outlet temperatures of 27–33°C (anode side), 20–29°C (cathode side), cell voltages of 3.0–4.2 V (at current density of 1.2–2.4 kAm^–2) and a fixed temperature of 70°C in the anolyte tank.The effects of superficial current density, NaOH concentration (0.5–2.0 M) and catholyte liquid loadings (0.92–4.6 kg m^–2 s^–1) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxyl mole ratio on the chlorate current efficiency was also determined.Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20.0 and 86.0%; chlorate current efficiency between 51.0 and 80.6% and peroxide concentration ranging from 0.069 to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4–2.8 M) and dilute (0–0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated a less than 0.4% chloride loss to the catholyte. The results are interpreted in terms of the electrochemistry, chemical kinetics and the hydrodynamics of the cell.Nomenclature C _i concentration of speciesi (mol m^–3) - F Faraday constant (96 500 C mol^–1) - I current (A) - Q catholyte flow rate (m³s^–1) - total time of cell operation (s) - _i current efficiency of speciesi (%)     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

The “In-cell” and “Ex-cell” Fenton treatment of phenol, 4-chlorophenol and aniline

A comparative study of phenol, 4-chlorophenol and aniline degradation with the electro-generation of H₂O₂ at gas-diffusion electrodes was carried out under three different conditions: electro-Fenton^® treatment in an undivided cell; electro-Fenton treatment in the catholyte of a membrane cell divided by a proton-exchange membrane (in-cell electro-Fenton membrane process); and a treatment of polluted solution in the cathode space of a membrane cell with the generation of H₂O₂, followed by the addition of Fe(II) salt in the other reactor (ex-cell electro-Fenton process).An optimized cell design with no gap between the membrane and the anode, along with the appropriate choice of supporting electrolytes, ensured a voltage reduction with a membrane cell in comparison with that of an undivided cell. The accumulation of hydrogen peroxide in concentrations sufficient for the almost complete destruction (90–98%) of aromatic organic pollutants was achieved in all cases but the ex-cell process with the preparative electrolysis in the pilot scale membrane reactor separated by the proton-exchange membrane MK-40 showed higher treatment efficiency and lower specific energy consumption in comparison with known technologies. Damage of the gas-diffusion layer was observed in some tests which could be caused by alkaline conditions in the pores of the gas-diffusion cathode (GDE). The pH indicator paper showed a color specific for alkaline media in contact with the GDE treated in the solution with pH 3 in the bulk. A possible explanation could be that even in acid media, hydrogen peroxide generation in pores of the gas diffusion layer proceeds with formation of HO ₂ ^? which is common for alkaline media and consecutive protonation occurs at the interface with the acid solution.     

Electrogeneration of hydrogen peroxide in seawater and application to disinfection

The cathodic electrogeneration of hydrogen peroxide in seawater by means of oxygen reduction on a gas diffusion cathode was studied. The effects on the reaction yield of several operative parameters such as cell design, medium composition, anolyte concentration, pH and working potential were investigated. Results indicate that in a two-compartment cell notable concentrations of hydrogen peroxide are obtained with a constant yield in a wide range of charge. Lower catholyte pH values, obtainable by means of the anolyte choice, mitigate the decrease in the efficiency due to cathode fouling. Application of hydrogen peroxide electrogeneration to seawater disinfection was also tested. Comparative tests conducted using both commercial and electrogenerated hydrogen peroxide, either alone or combined with iron in Fenton’s treatment, are also presented.     

Comparative study of hydrogen peroxide electro-generation on gas-diffusion electrodes in undivided and membrane cells

The generation of hydrogen peroxide by means of the cathodic reduction of oxygen at gas-diffusion electrodes with a near 100% current efficiency was achieved in concentrations sufficient for the mineralization of refractory organics in Fenton treatment. A decrease in current efficiency over time at high temperatures and high current densities was observed. The polarization study carried out in potentiostatic, potentiodynamic and galvanostatic modes in 0.5 M Na₂SO₄ solution at pH 3 showed that the destruction of hydrogen peroxide at the cathode of the electrochemical reactor, as well as its chemical decomposition in the bulk solution, takes place at a significantly lower rate than the oxidation of H₂O₂ at the Ti–IrO₂ anode. Preparative electrolysis in the membrane reactor showed much higher current efficiencies for H₂O₂ electro-generation in comparison with tests carried out in an undivided cell. The performance of different proton-exchange membrane in this process was studied and a membrane cell with a heterogeneous MK-40 type PEM was found to be suitable. An optimized cell design, the appropriate selection of electrodes, supporting electrolytes, and a membrane resulted in a lower voltage in the membrane cell in comparison with the undivided cell.     

An experimental study of a fixed bed chlor-alkali reactor

A 100 A continuous ‘flow-by’ chlor-alkali membrane reactor was constructed with both anode and cathode consisting of fixed beds of 0.6 to 1 mm diameter graphite particles. The reactor was operated over a range of conditions with and without co-current flow of air or oxygen to the cathode. With an anolyte of 5 M NaCl and catholyte 1.4–3 M NaOH the reactor produced sodium hydroxide and chlorine with ≥80% efficiency at temperatures 28–100°C, absolute pressure 270–970 kPa and superficial current density up to 3.3 kA m^?2. For operation at 100°C and an average pressure of 870 kPa with no gas delivered to the cathode, the cell voltage increased linearly from 2.5V at 0.3 kA m^?2 (10 A) to 4.0 V at 3.3 kA m^?2 (100 A). When oxygen was delivered to the cathode at 1 litre min^?1 under 870 kPa average pressure, the corresonding cell voltages were 1.6 V at 0.3 kA m^?2 to 3.4 V at 3.3 kA m^?2. In operation with air under the same conditions the cell voltage rose from 1.6 V at 0.3 kA m^?2 to 3.1 V at 1.6 kA m^?2. The performance of the oxygen cathode deteriorated with lower pressure and temperature due to mass transfer constraints on the oxygen reaction in the fixed bed electrode.     

Sauerstoff-Verzehrkathoden für die Chloralkali-Elektrolyse

Oxygen-consuming cathodes for alkali chloride electrolysis. Considerable energy saving can be accomplished in alkali chloride electrolysis if an oxygen-consuming cathode is used in place of one liberating hydrogen. An overall cell potential saving of ca. 1 V is possible. In particular, diaphragm cells are suitable for air cathodes owing to the high purity of the catholyte. A possible altenative to the use of an in-situ air cathode is the use of hydrogen/air fuel cells, such as the phosphoric acid system of United Technologies, for electrochemical utilization of the hydrogen. The operating temperature is then 200 °C at most. The waste heat can be utilized for evaporation of, e.g., diaphragm cell caustic soda; this acid system also requires no prior air purification. However, the gain in energy is only two thirds of that accomplished with an in-situ cathode. At present, great effort is being invested in the development of favourably-priced air cathodes with long lifetimes in concentrated caustic soda; apart from platinum, numerous transition metal complexes are being tested for this purpose.     

Influence of anolyte and catholyte composition on TPHs removal from low permeability soil by electrokinetic reclamation

Removal of TPHs from polluted soil by electrokientic reclamation was done by using different electrolytes (anolyte and catholyte). The initial concentration of TPHs in soil was 23,000 ppm and removal efficiencies reached almost 90% for a combination of 0.04 M NaOH and 0.1 M Na₂SO₄ in the anode and cathode chambers, respectively. Electroosmotic flow and TPHs desorption were measured under galvanostatic conditions (1.95 mA cm⁻² and electric field <10 V cm⁻¹). The study is supported on the electrokinetic transport model for low permeability soils. Electrolytes (anolyte and catholyte) were maintained at constant ionic composition to keep constant boundary conditions, thus launch a pseudostationary state for fluid and charge transport throughout the soil. It was also observed that electrolyte concentration favored TPHs desorption as well as their transport throughout the soil by electroosmotic flow from anode to cathode. Both, electrolytes concentration and wetting solution helped to maintain a constant pH profile during electroreclamation, thus a sustained fluid flow from anode to cathode.     

影响离子膜电解槽槽电压的因素

阐述了离子膜电解槽操作温度、电流密度、电解液流量、阴极液质量分数、阳极液质量分数、阳极液ｐＨ值、阳极液中金属离子以及阴极材料等九方面对电解槽电压的影响。     

Scale-up of an electrochemical cell for oxygen removal from water

In a previous paper an electrochemical method for the removal of dissolved oxygen from water was described. In that work the oxygen-rich water was passed through a three-dimensional cathode and the dissolved oxygen was reduced on the cathode surface to water. In the present study electrochemical oxygen removal and, especially, the scale-up of the deoxygenation cell were investigated. The volume of the three-dimensional cathode was enlarged and suitable cathode materials and membranes were tested. The maximum flow rate and the optimum cell voltage were determined. Finally, two cathodes were connected in parallel flow. A flow rate ten times higher than that of the former laboratory-scale cell was achieved. Over 99.95% of the dissolved oxygen was removed. No significant amount of by-products, hydrogen or hydrogen peroxide, was observed.Nomenclature A area of the membrane (m²) - D hydrodynamic permeability (g s^–1 m^–2 bar^–1) - F Faraday number (96 500 A s mol^–1) - I current (A) - I _meas measured current (A) - I _theor theoretical current (A) - M _i molecular mass of species i (g mol^–1) - flow rate (g[water] s^–1) - m _de mass of water decomposed on the anode (g) meomass of water transported through the membrane by the electroosmosis (g) - m _ev mass of water evaporated with the gaseous oxygen (g) - m _p mass of water transported through the membrane due to the pressure (g) - m _tot total mass change of the anolyte (g) - N _w water transference number (2.2) - p pressure of the gas bubble (pressure of the air, 101 300 Pa) - pH₂O water vapour pressure at room temperature (3000 Pa) - P pressure difference between catholyte and anolyte (bar) - [O₂] mass fraction of dissolved oxygen (g[O₂] g[water]^–1) - t time (s) - z _i number of electrons needed per species i     

Electrochemical synthesis of N2O5 by oxidation of N2O4 in nitric acid with PTFE membrane

Electrochemical synthesis of dinitrogen pentoxide (N₂O₅) by oxidation of dinitrogen tetroxide (N₂O₄) in a plate-and-frame electrolyzer was investigated. As the separator, different porous polytetrafluoroethylene (PTFE) membranes were tested in this process and the effects of hydrophilicity and of hydrophobicity on the electrolysis were discussed. The transport of N₂O₄ and water from catholyte to anolyte through membrane occurred in the electrolysis, especially at the end of the electrolysis. The water transport had a much more effect on the electrolysis than that of the N₂O₄ diffusion. The hydrophobic PTFE membranes had better performance on control of water transport from catholyte to anolyte than that of the hydrophilic ones. Hydrophobicity can increase the chemical yield of N₂O₅. The membranes with a low hydrophobic surface were preferred. All the hydrophobic PTFE membranes with low resistance have the specific energy of 1.1-1.5 kWh kg⁻¹ N₂O₅. The current efficiency of 67.3-80.2% and chemical yield of 58.9-60.9% were achieved in production of N₂O₅. The technique of replacing the catholyte with fresh nitric acid can minimize the transport of N₂O₄ and water to a great extent, it can further improve the chemical yield and reduce the specific energy.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

The vertical distribution of current in a gas-evolving membrane cell

A one-dimensional numerical model to describe gas void fraction and current distribution in five model membrane cell configurations is described in this work. The five models describe ideal (equipotential), upright (top cathode/bottom anode), inverted, u- and n-type electrical connections with anodic chlorine and cathodic hydrogen evolution in each case. In all but the first case the finite resistances of the electrodes are taken into account. The effects of (a) different terminal arrangements, (b) different current densities, (c) different cell heights, (d) different compartment widths, and (e) different overvoltages, have been investigated. For each study the current distribution and anolyte and catholyte void fraction distribution is displayed. The resistive components of the cell voltages are also calculated; the calculated resistive voltage loss varies between extremes of 0.291 V for the ideal cell to 0.377 V for the inverted cell at 3 kA m^–2 and 0.25 m cell height with typical fixed values of other parameters.Nomenclature A cross-sectional area - d bubble diameter - void fraction - _m maximum void fraction - G gas volumetric flow rate - K ratio of conductivities of bubble-free and bubble-filled electrolyte - L liquid volumetric flow rate - electrolyte viscosity - R _AN,R _A resistances of anode, anolyte, membrane - R _M,R _C cathode and catholyte, respectively (see - R _CA resistive network scheme of Fig. 2) - _L, _G liquid and gas phase densities - u ₁ single bubble rise velocity - u _sw bubble swarm rise velocity Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

An electrochemical membrane reactor with three compartments (anolyte, catholyte and central compartment) based on in-house-prepared cation- and anion-exchange membrane was developed to achieve in situ separation and recovery of chromic acid and metal ions. The physicochemical and electrochemical properties of the ion-exchange membrane under standard operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of chromate and dichromate of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that metal ion migrated through the cation-exchange membrane from central compartment to catholyte and OH⁻ formation at the cathode leads to the formation of metal hydroxide. Simultaneously, chromate ion migrated through the anion-exchange membrane from central compartment to the anolyte and formed chromic acid by combining H⁺ produced their by oxidative water splitting. Thus a continuous decay in the concentration of chromate and metal ion was observed in the central compartment, which was recovered separately in the anolyte and catholyte, respectively, from their mixed solution. This process was completely optimized in terms of operating conditions such as initial concentration of chromate and metal ions in the central compartment, the applied cell voltage, chromate and metal ion flux, recovery percentage, energy consumption, and current efficiency. It was concluded that chromic acid and metal ions can be recovered efficiently from their mixed solution leaving behind the uncharged organics and can be reused as their corresponding acid and base apart from the purifying water for further applications.     

Nanostructured palladium-silver coated nickel foam cathode for magnesium-hydrogen peroxide fuel cells

A novel multiscale Pd-Ag catalyzed porous cathode for the magnesium-hydrogen peroxide fuel cell was prepared by electrodeposition of Pd onto Ag coated nickel foam surface from an aqueous solution of palladium chloride. The structure, morphology and composition of the electrodeposited catalyst layer were characterized using SEM, EDS and XPS analysis. Magnesium-hydrogen peroxide fuel cell tests with the Pd-Ag deposited cathode were carried out and compared with the Ag-deposited electrode. The effects of temperature, H₂O₂ flow rate and H₂O₂ concentration on cell performance were investigated, and the electrode stability test was carried out. The Pd-Ag deposited electrode showed higher catalytic activity for the reduction of hydrogen peroxide than that of the Ag-deposited Ni foam cathode, and gave much improved fuel cell performance. The magnesium-hydrogen peroxide fuel cell with nanostructured Pd-Ag coated nickel foam cathode presented a maximum power density of 140 mW cm⁻², but the Mg-H₂O₂ fuel cell with Ag coated Ni foam cathode gave only 110 mW cm⁻² under the same operation condition.     

Transport and conductivity properties of an advanced cation exchange membrane in concentrated sodium hydroxide

An electrochemical concentrator for application to the chlorine-caustic industry is currently under development. In it 30 to 35 wt % NaOH enters the anolyte and catholyte chambers and exits at 20 and 50 wt %, respectively. Consequently, in support of the electrochemical concentrator development, the conductance and transport properties of advanced cation exchange membranes in concentrated sodium hydroxide, are being investigated. The membrane voltage drop, sodium ion transport and water flux of these membranes in 20 to 35 wt % sodium hydroxide anolyte and 30 to 50 wt % sodium hydroxide catholyte at 75°C are presented. To better understand the behaviour of these membranes, electrolyte sorption measurements were conducted in the anolyte/catholyte environment appropriate for the electrochemical concentrator. The water uptake data appear to correlate well with the conductance data and the combined NaOH and water sorption data are consistent with the sodium ion transport data.     

PAIRED ELECTRO-GENERATION OF GLYOXYLIC ACID USING BIPOLAR MEMBRANE MADE FROM SODIUM ALGINATE AND CHITOSAN

Sodium alginate (SA) and chitosan (CS) were modified with Ca²⁺ and glutaraldehyde linking reagents to prepare the mSA/mCS bipolar membrane (BPM). The morphology of the membrane was characterized by SEM. The membrane was used as a separator in an electrolysis cell for the production of glyoxylic acid simultaneously at both the cathode and the anode. The catholyte consisted of a mixture of saturated oxalic acid and 0.1 mol/L HCl, and the anolyte was a mixture of glyoxal (10 wt.%) and KBr (10 wt.%). A nickel mesh was placed on the surface of the mSA cation exchange layer to act as the cathode, and the anode was PbO₂. The electrolysis voltage was as low as 2.7 V during operation at room temperature with a current density of 20 mA · cm^?2. Current efficiencies reached 82.9% in the cathode chamber and 75.7% in the anode chamber.