Chlor-alkali Electrolysis Research Articles

Service life test of the NiSn coatings as cathodes for hydrogen evolution in industrial chlor-alkali electrolysis

In this work the “service life test” (SLT) of the NiSn alloy coatings as cathodes for the hydrogen evolution reaction (HER), deposited onto Ni 40 mesh at different current densities from the bath containing 0.1 mol dm−3 SnCl2 + 0.3 mol dm−3 NiCl2 + 0.6 mol dm−3 K4P2O7 + 0.3 mol dm−3 NH2CH2COOH at 50 °C, was investigated and compared with that recorded for the commercial Ni–RuO2 De Nora's (DN) cathode. The morphology and chemical compositions of all NiSn samples were investigated by SEM and EDS techniques before and after the SLT. HER during the SLT has also been monitored by EIS technique. The chemical compositions of surfaces of all NiSn alloy samples, as well as EIS results, were found to depend on the number of cycles performed during the SLT. The decrease of their catalytic activity for the HER in 32 wt.% NaOH at 90 °C with increasing the number of cycles (about 20–25 mV after 25 cycles) was practically identical to that for DN cathode, while NiSn samples deposited at −30 mA cm−2, −60 mA cm−2 and −100 mA cm−2 possessed lower overpotential for the HER before and after SLT in comparison with that for the DN cathode. It is confirmed by the SEM–EDS and EIS analysis of the NiSn samples that the minor loss of the catalytic activity for the HER is the consequence of the change of chemical composition of NiSn coatings and decrease of the active surface area. This decrease is ascribed to partially eroded NiSn coatings due to oxygen evolution during the SLT.

Impact of the spatial distribution of morphological pattern on the efficiency of electrocatalytic gas evolving reactions

The efficiency of electrocatalytic gas evolving reactions (hydrogen, chlorine and oxygen evolution) is a key challenge for the important industrial processes, such as chlor-alkali electrolysis or water electrolysis. Central issue for the aforementioned electrocatalytic processes is huge power consumption. Experimental results accumulated in the past, as well as some predictive models ("volcano" plots) indicate that altering the nature of the electrode material cannot significantly increase the activity of mentioned reactions. Consequently, it is necessary to find a qualitatively different strategy for improving the energy efficiency of electrocatalytic gas evolving reactions. Usually disregarded fact is that the gas evolution is an oscillatory phenomenon. Given the oscillatory behavior, a key parameter of macrokinetics of gas electrode is the frequency of gas-bubble detachment. Bearing in mind that the gas evolution greatly depends on the surface morphology, a methodology is proposed that establishes a rational link between the morphological pattern of electrode with electrode activity and stability. Characterization was performed using advanced analytical tools. Frequency of gas-bubble detachment is obtained in the configuration of scanning electrochemical microscopy (SECM) while the corrosion stability is analyzed using miniaturized scanning flow electrochemical cell connected to the mass spectrometer (SFC-ICPMS).

Electrodeposited, Ni-based, non-noble metal coatings as cathodes for hydrogen evolution in chlor-alkali electrolysis

The hydrogen evolution reaction (HER) has been investigated on two types of electrodeposited, Nibased, non-noble metal coatings: composite coatings with inclusion of MoO2 particles and electrodeposited NiSn alloy coatings, in order to find suitable replacement for noble metal coatings (commercial De Nora's Ni-RuO2 electrode (DN)), as cathodes for industrial application in the zero-gap membrane cell for chlor-alkali electrolysis. Some samples of both types of cathodes showed better catalytic activity for the HER than the DN electrode under the conditions of industrial applications: 32 mass % NaOH at 90°C and j = -0.3 A cm-2. Since lower overvoltage for the HER is not the only criteria for successful application in industrial electrolysis, service life test (SLT), simulating long time operation of cathodes, has been applied for both types of cathodes. It has also been shown that certain samples of both types of cathodes could be promising replacement for the commercial DN electrode since they showed better performance during the SLT.

Copper/Carbon/PTFE Oxygen-Depolarized Cathodes for Chlor-alkali Membrane Cells

Chlor-alkali electrolysis continues to pose challenges for researchers. Replacement of the hydrogen-evolution reaction by the oxygen-reduction reaction can reduce the overpotential of the cathodic process, depolarizing the overall reaction and saving energy. Here, we describe a series of experiments to determine the cell voltage and energy savings when a copper-doped carbon/polytetrafluoroethylene (PTFE) oxygen-diffusion cathode is used in brine electrolysis experiments, instead of a hydrogen-evolving graphite cathode. Voltammetric studies were carried out to determine the ideal oxygen flow rate through the porous cathode structure and the amount of copper that maximizes oxygen-reduction current densities. Brine electrolysis was performed in a two-compartment membrane cell using a TiO2/RuO2 anode. Our findings indicate a strong depolarizing effect with the copper-doped oxygen-diffusion cathode. Comparison of the results using a graphite (hydrogen-evolving) cathode and a copper-doped cathode at 70 °C showe...

Anodic Electrocatalytic Coatings for Electrolytic Chlorine Production: A Review

AbstractIndustrial chlor-alkali electrolysis represents one of the most energy- and resource-intensive technological applications of electrocatalysis. Improving process efficiency becomes a critical issue for the sustainable development and for alleviating the energy and environmental crisis. Rational design in the morphology of RuO2-based anodic electrocatalytic coatings and the control in the coating microstructure can contribute to massive energy saving compared to the current commercial Ru0.3Ti0.7O2coating. This review covers recent developments in the anodic coatings. Performance enhancement for RuO2-based anodic coatings is achieved by using alternative preparation routes of sol-gel and electrodeposition. The target control in the coating surface morphologies and the increase in the utilization of active Ru species are demonstrated.

Comparative LCA of multi-product processes with non-common products: a systematic approach applied to chlorine electrolysis technologies

Purpose Multi-product processes are one source of multi-functionality causing widely discussed methodological problems within life cycle assessment. A multi-functionality problem exists for comparative life cycle assessment (LCA) of multi-product processes with non-common products. This work develops a systematic workflow for fixing the multi-functionality problem caused by the non-common products. A novel technology for chlor-alkali electrolysis is analyzed and compared to the industrial standard technology to illustrate the approach and to benchmark the new technology's environmental impact.

Oxygen Reduction Electrocatalyst Based on Strongly Coupled Cobalt Oxide Nanocrystals and Carbon Nanotubes

Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs. The mildly oxidized CNTs provided functional groups on the outer walls to nucleate and anchor nanocrystals, while retaining intact inner walls for highly conducting network. Cobalt oxide was in the form of CoO due to a gas-phase annealing step in NH(3). The resulting CoO/nitrogen-doped CNT (NCNT) hybrid showed high ORR current density that outperformed Co(3)O(4)/graphene hybrid and commercial Pt/C catalyst at medium overpotential, mainly through a 4e reduction pathway. The metal oxide/carbon nanotube hybrid was found to be advantageous over the graphene counterpart in terms of active sites and charge transport. Last, the CoO/NCNT hybrid showed high ORR activity and stability under a highly corrosive condition of 10 M NaOH at 80 °C, demonstrating the potential of strongly coupled inorganic/nanocarbon hybrid as a novel catalyst system in oxygen depolarized cathode for chlor-alkali electrolysis.

Identification and molecular analysis of mercury resistant bacteria in Kor River, Iran

Mercury (Hg) is one of the most important toxic pollutants widespread in the environment. It is being extensively used in industrial applications (chlor-alkali electrolysis, fungicides, disinfectants, dental products, etc), resulting in local hot spots of pollution and serious effects on biota and humans. The aim of this study was to identify mercury resistant bacteria and extract their plasmids and DNA. In this study, mercury-resistant bacteria were isolated and characterized from mercury-polluted sediments in Kor River in Iran. The samples were cultured in different media cultures, identified using biochemical tests, and due to the relationship between antibiotic and mercury resistance, they were isolated based on these two factors. The plasmids and DNA were extracted from the most resistant bacteria to both antibiotic and mercury and the sizes were determined using agarose gel electrophoresis. A 12.3 Kb plasmid from Serattia sp. and Escherichia coli and using Sau3A1 enzyme, some DNA fragments (4, 6, 8 and 10 Kb) from Pseudomonas sp., Serattia sp. and Escherichia coli were also extracted. Key words: Mercury, resistant, bacteria, DNA, plasmid extraction, restriction endonuclease.

Development of high-performance silver-based gas-diffusion electrodes for chlor-alkali electrolysis with oxygen depolarized cathodes

Silver-based gas-diffusion electrodes were prepared, characterized and tested during chlor-alkali electrolysis with oxygen depolarized cathodes. Spraying of aqueous suspensions containing silver catalyst particles, a PTFE suspension, a surfactant and an organic thickening agent on nickel nets followed by drying, hot-pressing and sintering allowed for the preparation of highly active electrodes. Electrodes obtained from the most suitable catalyst SF9ED (Ferro) were systematically investigated. The best electrodes contain 97–98wt.% silver and 2–3wt.% PTFE, are hot-pressed at ca. 130°C with moderate pressure and subsequently sintered at temperatures around 340°C. For these electrodes, half cell potentials of ca. 650mV vs. RHE corresponding to electrolysis cell voltages of ca. 2.17V at current densities of 4kA/m2 were obtained. Both half cell and electrolysis cell voltages were found to be reproducible within about ±30mV during repeated measurements using electrodes from different batches. While the Ag/PTFE loading had little influence on the observed voltages in the range studied (100–300mg/cm2), loadings of at least 200mg/cm2 are recommended to prevent leakage of NaOH electrolyte and to allow for operation under oxygen overpressures of more than 100mbar without breakthrough of gas to the electrolyte.

Thin-film flooded agglomerate model for silver-based oxygen depolarized cathodes

A mathematical model for a porous, silver-based electrode for the oxygen reduction in alkaline solutions, based on the thin film flooded agglomerate theory, was developed. These electrodes are employed in the energy-efficient chlor-alkali electrolysis with oxygen depolarized cathodes. The model parameters were determined from overpotentials at different oxygen concentrations obtained in half-cell measurements. For the description of the reaction kinetics, it was necessary to introduce two Tafel equations, which might be explained by a change of the adsorption isotherm of the intermediate species during oxygen reduction. The model allows for a successful description of the overpotentials in the region of industrially relevant current densities. The analysis of the oxygen concentration distribution in the liquid electrolyte reveals that massive diffusion limitations occur although the calculated size of the agglomerates is only in the range of a few micrometers.

Comparative Study on Application of Bimetallic Pt-Based Alloy Electrocatalysts in Advanced Chlor-Alkali Electrolysis

Application of an oxygen-depolarized cathode will contribute to energy saving in chlor-alkali electrolysis. For this purpose, the development of high-performance cathode with the best electrocatalyst is essential. Using bimetallic Pt-based alloy electrocatalysts including PtPd and PtAg carbon-supported in oxygen-depolarized cathode chlor-alkali cell has been shown to have the high cell performance. This study presents application of PtRu carbon supported electrocatalyst oxygen-depolarized cathode and performance comparison of cells with carbon-supported PtRu, PtPd and PtAg electrocatalysts cathodes using the same DSA-Cl2 anode. Results show that there are quite similarity between the effects of various factors on the caustic current efficiency (CCE) in a zero-gap oxygen-depolarized chlor-alkali cells employing carbon-supported PtPd, PtRu and PtAg electrocatalysts. Besides, it seems that the PtPd/C electrocatalyst cathode has relatively higher performance than the other cathodes with PtAg/C and PtRu/C electrocatalysts in zero-gap chlor-alkali cells.

Fuel cells: problems and solutions

Preface. Symbols. Acronyms and Abbreviations. PART I: INTRODUCTION. Introduction. Chapter 1: The Working Principle of a Fuel Cell. 1.1 Thermodynamic Aspects. 1.2 Schematic Layout of Fuel Cell Units. 1.3 Types of Fuel Cells. 1.4 Layout of a Real Fuel Cell: The Hydrogen-Oxygen Fuel Cell with Liquid Electrolyte. 1.5 Basic Parameters o Fuel Cells. Chapter 2: The Long History o Fuel Cells. 2.1 The Period Prior t 1894. 2.2 The Period from 1894 to 1960. 2.3 The Period from 1960 to the 1990s. 2.4 The Period after the 1990s. PART II: MAJOR TYPES OF FUEL CELLS. Chapter 3: Proton-Exchange Membrane Fuel Cells (PEMFC). 3.1 History of the PEMFC. 3.2 Standard PEMFC Version from the 1990s. 3.3 Special Features of PEMFC Operation. 3.4 Platinum Catalyst Poisoning By Traces of CO in the Hydrogen. 3.5 Commercial Activities in Relation to PEMFC. 3.6 Future Development of PEMFC. 3.7 Elevated-Temperature PEMFC (ET-PEMFC). Chapter 4: Direct Liquid Fuel Cells. Part A: Direct Methanol Fuel Cells. 4.1 Methanol as Fuel for Fuel Cells. 4.2 Current-Producing Reaction and Thermodynamic Parameters. 4.3 Anodic Oxidation of Methanol. 4.4 Milestones in DMFC Development. 4.5 Membrane Penetration by Methanol (Methanol Crossover). 4.6 Varieties of DMFCs. 4.7 Special Operating Features of DMFCs. 4.8 Practical Models of DMFCs and their Features. 4.9 Problems To Be Solved In Future DMFCs. Part B: Direct Liquid Fuel Cells. 4.10 The Problem of Replacing Methanol. 4.11 Fuel Cells Using Organic Liquids as Fuels. 4.12 Fuel Cells Using Inorganic Liquids as Fuels. Chapter 5: Phosphoric Acid Fuel Cells. 5.1 Early Work on Phosphoric Acid Fuel Cells. 5.2 Special Features of Aqueous Phosphoric Acid Solutions. 5.3 Construction of PAFCs. 5.4 Commercial Production of PAFCs. 5.5 Development of Large Stationary Power Plants. 5.6 The Future for PAFCs. 5.7 Importance of PAFCs for Fuel Cell Development. Chapter 6: Alkaline Fuel Cells. 6.1 Hydrogen-Oxygen AFCs. 6.2 Alkaline Hydrazine Fuel Cells. 6.3 Anion-Exchange (Hydroxyl Ion Conducting) Membranes. 6.4 Methanol Fuel Cells with Anion-Exchange Membranes. 6.5 Methanol Fuel Cell with an Invariant Alkaline Electrolyte. Chapter 7: Molten Carbonate Fuel Cells. 7.1 Special Features of High-Temperature Fuel Cells. 7.2 Structure of Hydrogen-Oxygen MCFCs. 7.3 MCFCs with Internal Fuel Reforming. 7.4 Development of MCFC Work. 7.5 The Lifetime of MCFCs. Chapter 8: Solid-Oxide Fuel Cells. 8.1 Schematic Design of Conventional SOFCs. 8.2 Tubular SOFCs. 8.3 Planar SOFCs. 8.4 Monolithic SOFCs. 8.5 Varieties of SOFCs. 8.6 Utilization of Natural Fuels in SOFCs. 8.7 Interim-Temperature SOFCs. 8.8 Low-Temperature SOFCs. 8.9 Factors Influencing the Lifetime of SOFCs. Chapter 9: Other Types of Fuel Cells. 9.1. Redox Flow Cells. 9.2 Biological Fuel Cells. 9.3 Semi-Fuel Cells. 9.4 Direct Carbon Fuel Cells. Chapter 10: Fuel Cells and Electrolysis Processes. 10.1 Water Electrolysis. 10.2 Chlor-Alkali Electrolysis. 10.3 Electrochemical Synthesis Reactions. PART III: INHERENT SCIENTIFIC AND ENGINEERING PROBLEMS. Chapter 11: Fuel Management. 11.1 Reforming of Natural Fuel. 11.2 Production of Hydrogen For Autonomous Power Plants. 11.3 Purification of Technical Hydrogen. 11.4 Hydrogen Transport and Storage. Chapter 12: Electrocatalysis. 12.1 Fundamentals of Electrocatalysis. 12.2 Putting Platinum Catalysts on the Electrodes. 12.3 Supports For Platinum Catalysts. 12.4 Platinum Alloys and Composites as Catalysts for Anodes. 12.5 Non Platinum Catalysts for Fuel Cell Anodes. 12.6 Electrocatalysis of the Oxygen Reduction Reaction. 12.7 The Stability of Electrocatalysts. Chapter 13: Membranes. 13.1 Fuel-Cell-Related Membrane Problems. 13.2 Work to Overcome Degradation of Nafion Membranes. 13.3 Modification of Nafion(r) Membranes. 13.4 Membranes Made From Polymers Without Fluorine. 13.5 Membranes Made from Other Materials. 13.6 Matrix-Type Membranes. 13 7 Membranes with Hydroxyl Ion Conduction . Chapter 14: Small Fuel Cells for Portable Devices. 14.1 Special Operating Features of Mini-Fuel Cells. 14.2 Flat Miniature-Fuel Batteries. 14.3 Silicon-Based Mini-Fuel Cells. 14.4 PCB-Based Mini-Fuel Cells. 14.5 Mini-Solid Oxide Fuel Cells. 14.6 The Problem of Air-Breathing Cathodes. 14.7 Prototypes of Power Units with Mini-Fuel Cells. 14.8 Concluding Remarks. Chapter 15: Mathematical Modeling of Fuel Cells (Felix N. Buchi). 15.1 Zero-Dimensional Models. 15.2 One-Dimensional Models. 15.3 Two Dimensional Models. 15.4 Three Dimensional Models. 15.5 Concluding Remarks . PART IV: COMMERCIALIZATION OF FUEL CELLS. Chapter 16: Applications. 16.1 Large Stationary Power Plants. 16.2 Small Stationary Power Units. 16.3 Fuel Cells for Transport Applications. 16.4 Portables. 16.5 Military Applications. Chapter 17: Fuel Cell Work In Various Countries. 17.1 Driving Forces for Fuel-Cell Work. 17.2 Fuel Cells and the Hydrogen Economy. 17.3 Activities in North America. 17.4 Activities in Europe. 17.5 Activities in Other Countries. 17.6 The Volume of Published Fuel-Cell Work. 17.7 Legislation and Standardization in the Field of Fuel Cells. Chapter 18: Outlook. 18.1 Periods of Alternating Hope and Disappointment Forever? 18.2 Some Misconceptions (Klaus Muller). 18.3 Ideal Fuel Cells. 18.4 Projected Future of Fuel Cells. General Bibliography. Author Index. Subject Index.

Chlor-alkali electrolysis with oxygen depolarized cathodes: history, present status and future prospects

The historical development, current status and future prospects of chlor-alkali electrolysis with oxygen depolarized cathodes (ODCs) are summarized. Over the last decades, membrane chlor-alkali technology has been optimized to such an extent that no substantial reduction of the energy demand can be expected from further process modifications. However, replacement of the hydrogen evolving cathodes in the classical membrane cells by ODCs allows for reduction of the cell voltage and correspondingly the energy consumption of up to 30%. This replacement requires the development of appropriate cathode materials and novel electrolysis cell designs. Due to their superior long-term stability, ODCs based on silver catalysts are very promising for oxygen reduction in concentrated NaOH solutions. Finite-gap falling film cells appear to be the technically most mature design among the several ODC electrolysis cells that have been investigated.

Polychlorinated naphthalenes and other dioxin‐like compounds in Elbe River sediments

Contamination of Elbe River (Germany) sediments with dioxin-like toxicants was investigated following the 500-year flood (flood that statistically occurs once in 500 years) of 2002. It was hypothesized that large amounts of particulate matter from river beds and associated dioxin-like toxicants were mobilized and transported during this flood event. The investigation focused on polychlorinated naphthalenes (PCNs) that have not been determined previously in the Elbe River. The in vitro H4IIE-luc assay was used as an overall measure for toxicants capable of binding to the aryl hydrocarbon receptor (AhR). The assay was combined with congener-specific instrumental analyses and fractionation to quantify PCN contributions to total AhR-mediated activity relative to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs). Penta- to octachloronaphthalene concentrations of 30 ng/kg dry weight up to 13 microg/kg dry weight were found in Elbe River sediments downstream of Bitterfeld. Concentrations of penta- to octachloronaphthalenes, however, were only approximately 3 microg/kg dry weight at a site in the vicinity of Bitterfeld, where a level of approximately 3 mg/kg dry weight was reported before the flood. Also, the congener pattern of PCNs at this site changed after the flood, and PCN patterns reported previously for Bitterfeld and assigned to chlor-alkali electrolysis with graphite electrodes could now be observed at the sites from downstream of Bitterfeld and Magdeburg. Whereas PCDD/Fs dominated the dioxin-like activity in the middle and lower Elbe River, PCNs contributed as much as 10% of the total AhR-mediated activity. The contribution of PCBs was less significant (maximum, 0.2%). Thus, in Elbe River sediments, PCNs should be considered as relevant contaminants and be included in future monitoring and risk assessment programs.

Investigation of Chlor-Alkali Electrolysis Intensified by Super Gravity

The super gravity field was applied to chlor-alkali electrolysis. The effects of super gravity on hydrogen evolution reaction (HER) and chlorine evolution reaction (CER) were investigated by linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The relationship between the cell voltages and gravity coefficient was studied. The results indicated that, the gas evolution reactions were intensified by super gravity and gas product was easier to spillover from solution. The solution resistance would reduce with the increase of gravity coefficient. The cell voltages also decreased with the increase of gravity coefficient, and the higher the current density, the larger the degree of cell voltage reduction.

Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.

Oxygen reduction electrodes for electrolysis in chlor-alkali cells

Oxygen reduction electrodes, containing non-noble metal catalysts supported on high surface area carbon and wet-proofed with PTFE were tested under reaction conditions for the chlor-alkali electrolysis. Double-layer gas diffusion electrodes were prepared by rolling of an active layer and diffusion layer on a nickel wire screen, compressed and sintered at 300 °C. Electrochemical measurements for substantiating the activity and stability of the half-cells were conducted in 8 M NaOH by supplying oxygen at a cell temperature of 70 °C and a constant current load of 300 mA cm −2. An electrolysis cell with a dimensionally stable anode (DSA) and double-layered cathode was assembled, where 4.8 M NaCl and oxygen were supplied, respectively, for the production of chlorine and NaOH. The cell performances as well as stability of the electrodes were investigated at about 80 °C. This study shows that by replacing the high voltage consuming hydrogen-evolving reaction and by adopting highly active electrocatalysts as cathode materials, energy savings of more than 30% could be realized.

Electro-catalytic membrane reactors and the development of bipolar membrane technology

Membrane reactors are currently under extensive research and development. Hardly any concept, however, is realized yet in practice. Frequently, forgotten as membrane reactors are electro-catalytic membrane reactors where electrodes perform chemical conversations and membranes separate the locations of conversion. We review first a mature electromembrane technology: the chlor-alkali electrolysis. A second example is the polymer-electrolyte fuel cells (FC) as an emerging technology, which carries the potential to dramatically change society’s energy infrastructure. Finally, we extensively describe a technology where the membrane itself is catalytically effective, splitting water into protons and hydroxyl ions: bipolar ion-exchange membrane technology.

Electro-catalytic membrane reactors and the development of bipolar membrane technology

Membrane reactors are currently under extensive research and development. Hardly any concept, however, is realized yet in practice. Frequently, forgotten as membrane reactors are electro-catalytic membrane reactors where electrodes perform chemical conversations and membranes separate the locations of conversion. We review first a mature electromembrane technology: the chlor-alkali electrolysis. A second example is the polymer-electrolyte fuel cells (FC) as an emerging technology, which carries the potential to dramatically change society’s energy infrastructure. Finally, we extensively describe a technology where the membrane itself is catalytically effective, splitting water into protons and hydroxyl ions: bipolar ion-exchange membrane technology.

Effect of silver catalyst on the activity and mechanism of a gas diffusion type oxygen cathode for chlor-alkali electrolysis

Application of a gas-diffusion type oxygen cathode will contribute to energy saving in chlor-alkali electrolysis. For this purpose the development of gas-diffusion electrodes with high performance and durability is essential. We have investigated the performance for oxygen reduction and the mechanism of its on gas-diffusion electrodes with and without Ag catalyst in order to develop such oxygen cathodes with high performance and durability. It has been found that an electrode with no catalyst, that is, carbon support only in the reaction layer, shows electrochemical activity for oxygen reduction in 32 wt % NaOH at 80 °C and 1 atm O2, but loading of 2 mg cm−2 Ag of particle size 300 nm, not only improves the activity by about 100 mV but promotes the four-electron reduction to produce OH−, while H2O2 is the predominant reaction intermediate in the absence of the Ag catalyst. The production of H2O2 has been demonstrated by conducting CV measurements to detect H2O2 in the anodic scan after a cathodic sweep up to 0.3 V vs RHE. It has been shown that the gas-diffusion type oxygen cathode with Ag catalyst has the high performance and durability necessary for chlor-alkali electrolysis.