PTFE Oxygen-Depolarized Cathodes for Chlor-alkali

Article pubs.acs.org/IECR

Copper/Carbon/PTFE Oxygen-Depolarized Cathodes for Chlor-alkali Membrane Cells Raul S. Figueiredo,† Rodnei Bertazzoli,*,† and Christiane A. Rodrigues‡ †

Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas, Rua Mendeleyev 200, 13083-860, Campinas, São Paulo, Brazil ‡ Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo, Rua São Nicolau 210, 09913-030, Diadema, São Paulo, Brazil ABSTRACT: 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 copperdoped 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 showed that the latter resulted in 42% reduction in energy demand. hydrogen-evolving cathode (2.0−4.0 kA m−2).2−4 Despite the reduction in energy consumption, an economic analysis of the process is necessary as there are four major drawbacks: (a) hydrogen is no longer produced; (b) oxygen has low solubility in aqueous media; (c) pure oxygen is required rather than air; and (d) oxygen-reducing cathodes have poor physical stability during long-term operation. The low solubility of oxygen in aqueous solutions can be overcome by the use of an oxygen-fed gas-diffusion electrode (GDE), a three-dimensional porous electrode known in chloralkali processes as an oxygen-depolarized cathode (ODC). This type of cathode has a conductive porous structure through which oxygen percolates from one surface to another surface that is in contact with the electrolyte. To ensure the maximum reaction rate and maximum rate of chlorine production, the gas flow rate should be sufficient to meet the demand, avoiding mass transfer control of the reaction rate. Long-term stability can also be achieved since hydrogen peroxide attack can be minimized. ODCs are usually made of carbon-black graphite pigment hot-pressed with polytetrafluoroethylene (PTFE) particles.2,3 Oxygen reduction to water is a four-electron reaction and on carbon materials takes place in two steps with the formation of H2O2 after the exchange of the first two electrons.4−8 This is the main reason why the electrode degrades, most of the catalysts in the hydrophilic layer corrode, and the ODC floods.4−6 However, a metal-doped ODC can catalyze the reaction by which hydrogen peroxide is reduced to water and also catalyze the four-electron

1. INTRODUCTION The worldwide capacity for chlorine production exceeds 60 million metric tons per year, and the average electric power consumption per ton produced is 3.0 MWh.1 With such impressive numbers, it is only to be expected that this industrial activity should constitute a fertile ground for research. Over the past 40 years, the production of chlorine and caustic soda has gone through several changes, involving fields as diverse as materials science, electrocatalysis, and reengineering of the process itself (e.g., zero gap cell technology). The main focus of these research efforts has been to increase the yield of the chlorine-evolution reaction, save energy, and comply with requirements for a cleaner environment. Having successfully achieved these objectives, the focus of research has shifted to the other side of the electrolytic cell, and cathodic reactions have become the subject of studies into alternative means of reducing power consumption. Replacement of the hydrogen-evolution reaction by the oxygenreduction reaction can greatly reduce the overpotential of the cathodic process in the chlor-alkali cell. In this case, the overall chemical reaction in an electrolytic cell, which, with a hydrogen-evolving cathode, was 2H 2O + 2Cl− → Cl 2 + H 2 + 2OH−

(1)

becomes H 2O + 2Cl− +

1 O2 → Cl 2 + 2OH− 2

(2)

When the driving forces for eqs 1 and 2 are compared, it can be seen that the cell voltage for brine electrolysis is reduced by 1.23 V. However, under industrial operating conditions, a reduction of ∼0.8−1.0 V can be expected, corresponding to a reduction in electrical energy requirements of up to 30% at typical current densities used in membrane cells with a © 2013 American Chemical Society

Received: Revised: Accepted: Published: 5611

December March 21, March 26, March 26,

16, 2012 2013 2013 2013

dx.doi.org/10.1021/ie303484d | Ind. Eng. Chem. Res. 2013, 52, 5611−5615

Industrial & Engineering Chemistry Research

Article

%). Before PTFE was added, the carbon pigment was mixed with metallic Sigma−Aldrich copper powder (20 ± 5 μm diameter), in amounts ranging from 5% to 15% (wt %). The mixture was homogenized in a 4:1 water/isopropanol solution, which was dried at 110 °C for 24 h. A 200-mesh AISI 304 stainless-steel screen current collector was placed at the bottom of a pressing tool, which was then filled with the precursor mass. Sintered ODCs 2 mm thick and 10 or 20 mm in diameter were obtained after pressing for 1.5 h at 310 °C under a load of 146 kg cm−2. To measure the amount of oxygen passing through the ODCs and becoming available for reduction accurately, the permeability of the electrodes was determined. Given the difference between the size of the Printex carbon pigment and the size of the copper particles, increasing permeability is expected as the percentage of catalyst increases. ODC permeability to oxygen was evaluated for a Darcian laminar flow. After the 10 mm carbon/PTFE disks were positioned in the middle of a 1-m-long metallic tube, oxygen was inserted at one end at a controlled pressure and the flow rate measured at the opposite end. The permeability of the ODC was obtained from the slopes of the plots of oxygen flow rate, as a function of the pressure drop, by rewriting Darcy’s equation as follows:

reaction by reducing the overpotential of the oxygen-to-water reaction. Silver is, by far, the most widely used catalyst for doping ODCs.9−11 It promotes the four-electron reduction of O2 to OH− and reduces cell voltage by 0.1 V, compared to a carbon noncatalyzed ODC.10 Depending on the silver load, the service life of an electrode may reach more than three years for typical current densities.11 Segregation and loss of metal at the interface, a decrease in hydrophilic properties with time, and an increase in the precipitation of compounds from the reaction process may decrease ODC performance by occluding reaction pores.6 Some of these issues can be solved by using platinum, which is a classical catalyst capable of promoting the fourelectron reduction of oxygen5 that has been found to improve the service life of ODC.9,12,13 In large-scale brine electrolysis, nevertheless, the use of non-noble metals instead of platinum is preferred, because of their lower cost. The amount of platinum catalyst needed to ensure that an ODC has a long service life may be as high as 5.6 g for each square meter of electrode.9 In this context, studies carried out with H2/O2 polymerelectrolyte-membrane-fuel-cells (PEMFCs) with the goal of reducing the platinum load in the anode and cathode can be used as a basis for selecting new electrocatalysts for the oxygenreduction reaction. Several studies of PEMFC cathodes catalyzed with non-noble metals14,15 have used a lengthy, involved route to support iron, cobalt, and copper as macrocyclic transition-metal complexes (porphyrin or phthalocyanine) on carbon cathodes. A mixture of cobalt porphyrin and a perovskite supported on high-surface-area carbon has already been tested as an electrocatalyst in an ODC for chloralkali cells.16 Copper-porphyrin and copper-phthalocyanine supported on a carbon cathode have been reported to be inactive for oxygen reduction.14,15 However, Nabae et al.17 used a copper/carbon cathode to reduce oxygen in an H2/O2 PEMFC. They prepared carbon-supported copper using a simple inorganic route. Although the electrocatalytic activity of the copper/carbon cathode was not as good as that of the Pt/C cathode, copper showed fairly good activity for oxygen reduction. Using cyclic voltammetry experiments, Nabae et al. concluded that the electrocatalytic activity of the Cu/C cathode was based on a Cu/Cu2+ redox couple. They also concluded that copper acted as an adsorption site for oxygen, increasing the O2 → OH− reaction rate. Moreover, because of the preparation method used, XRD measurements and SEM observations revealed large particles of Cu 0 (∼2 μm) homogeneously distributed in the carbon matrix.17 Developing the idea of a less-expensive, easy-to-prepare, and easy-to-shape non-noble metal/carbon ODC, we used a copper/carbon/PTFE cathode in brine-electrolysis oxygenreduction experiments to evaluate the catalytic activity of this type of cathode for the four-electron oxygen-reduction reaction and its potential for saving energy and oxygen in the electrolytic process.

K=

QμL AΔP

(3)

where K is the permeability coefficient, Q the flow rate (L s−1), μ the viscosity of oxygen (cp), L the length of the porous media (cm), A the area of the ODC (cm2), and ΔP the pressure drop (N cm−2). The values used for the measurements were μ = 0.0181 cP, L = 0.2 cm, and A = 0.78 cm2. ΔP was varied from 1.2 N cm−2 to 7.0 N cm−2. 2.2. Voltammetric Studies and Solutions. A 320 g L−1 solution of NaOH was prepared and thoroughly bubbled with oxygen until saturation. A water-jacketed single-compartment electrochemical cell was used for the voltammetric experiments. The ODC potential was then scanned from open-circuit potential to more-negative values, using a saturated calomel electrode (SCE) as reference to determine the range of potentials that could be used for oxygen reduction. A 0.78 cm2 carbon/PTFE ODC and 1 cm2 Ti/Ru0.3Ti0.7O2 dimensionally stable-anode-type electrode were used as working and counter electrodes, respectively. 2.3. Electrolysis Experiments. Extensive brine-electrolysis experiments were carried out in a water-jacketed two-electrode two-compartment cell with a Nafion 424 membrane. As the main objective of this study is the performance comparison among cathode materials, the ohmic drop and its minimization were not taken into consideration in the design of the electrolysis cell. The anode/cathode distance in the electrolysis cell was 11 cm, with the membrane positioned midway between them. The volume of each compartment was 40 mL, and the area of each electrode 3.1 cm2. The anolyte and catholyte consisted of a 250 g L−1 solution of NaCl and a 320 g L−1 solution of NaOH, respectively. Experiments were run at temperatures of 25 and 70 °C. The current density during electrolysis was 2470 A m−2. An oxygen pressure of 0.2 kgf cm−2 was maintained on the back of the GDE. To quantify the evolving chlorine, a gas washer containing a 360 g L−1 solution of KI was attached to the anodic compartment. Since chlorine oxidizes iodide to iodine, iodometry with 0.1 N sodium thiosulfate was used to determine the amount of chlorine generated.

2. EXPERIMENTAL PROCEDURES 2.1. Preparation of a Copper-Doped ODC. The oxygen diffusion electrode used in this investigation was a single mechanically self-supporting layer with a stainless-steel screen current collector. Precursor mass for the ODC was prepared from Degussa Printex 6L conductive carbon-black graphite pigment. A 60% PTFE dispersion (3 M Dyneon TF 5035 PTFE) was used as a hydrophobic binder. The ratio of Printex to PTFE was 8:3.3 (w:w), giving a PTFE content of 20% (wt 5612



Article

3. RESULTS AND DISCUSSION 3.1. ODC Permeability. Figure 1 shows the results of elemental analysis using scanning electron microscopy, coupled

Figure 1. EDS analysis of a Cu (10 wt %)/GDE cathode. Figure 3. Linear potential scan on the surface of the Cu-free ODC for the O2 pressures shown with a 320 g L−1 solution of NaOH, pH 12.8, and a scan rate of 50 mV s−1.

with energy-dispersive spectroscopy (SEM/EDS). The peaks indicate the presence of carbon, fluorine, copper and oxygen. The first two elements are from the carbon pigment and PTFE, while copper and oxygen are elements in the catalyst. The average permeability of the as-prepared electrodes measured under a Darcian flow regime was calculated using eq 3, and the slopes of the lines are shown in Figure 2. It can be

Current recorded below −0.5 V is the result of two parallel processes: the reduction of hydrogen peroxide to water, as in eq 5, and the four-electron reduction of oxygen to water (eq 4 + eq 5). HO2− + H 2O + 2e− → 3OH−

Figure 3 also shows that the current increases with oxygen pressure up to 3.0 N cm−2. Above this pressure, the resulting curves are almost superimposed, with no further increase in the rate of the reduction reaction. As the electrode used in this experiment is copper-free and, therefore, has the lowest permeability, the choice of a pressure of 4.0 N cm−2 ensures there is sufficient excess reactant to cater to electrodes containing different amounts of copper. At this pressure, the oxygen flow rate is 2.6 × 10−5 L s−1 (see Figure 2). Next, the effect that the amount of copper had on an ODC was investigated by linear voltammetry. ODCs were mounted in the bottom of single-compartment cells and catalyzed with increasing percentages of copper, ranging from 0% to 15% (wt %). Figure 4 shows i−E couples recorded during a potential scan; the topmost curve is a reference curve obtained with the

Figure 2. Permeability of the ODC to O2, as a function of copper content.

seen that, generally, permeability increases as the amount of catalyst increases. This is because the electrode contains a mechanical mixture of carbon pigment and larger catalyst particles. 3.2. Voltammetric Experiments. As a GDE was used in this study to overcome the low solubility of oxygen in an aqueous medium and avoid control of the reduction reaction by mass transfer, it was important to determine the oxygen pressure needed to guarantee an excess of reactant. To identify the flow rate that satisfied this condition, a set of voltammetric i−E curves was recorded while the potential was scanned from 0.0 to −2.0 V vs SCE. An ODC without any copper was used. The resulting voltammetric curves for various oxygen pressures are shown in Figure 3. It can be seen that all the curves have two distinct sections with different slopes. The first section extends from 0.0 to −0.5 V and corresponds to the formation of hydrogen peroxide, as described by the equation for the reaction in an alkaline medium:7,17 O2 + H 2O + 2e− → HO2− + OH−

(5)

Figure 4. Linear potential scans on the surfaces of ODCs catalyzed with different amounts of copper (wt %) under N2 and an O2 pressure of 4.0 N cm−2 with a 320 g L−1 solution of NaOH and a potential scan rate of 50 mV s−1.

(4) 5613



Article

electrode, the anodic current response is a result of the chlorine evolution reaction. In Figure 6, the curve obtained

ODC kept under N2 pressure. As can be seen, when the ODC was pressurized with oxygen, the presence of copper resulted in a significant increase in current, compared to the copper-free electrode, particularly in the region where water was formed. However, the increase in current did not follow a regular trend, and the currents recorded for 10% copper content were higher than those for 15% content, a finding that could consistently be reproduced. For the curves corresponding to copper contents of 0% and 5%, two distinct wavy sections can be observed. The first section can be attributed to the formation of hydrogen peroxide, and the second to further reduction of hydrogen peroxide to water. At a concentration of 10%, the slope of the curve does not change and the i−E couples indicate that there is minimal, if any, formation of hydrogen peroxide, the current response corresponding mainly to the formation of water. When the copper concentration is further increased to 15%, the current decreases. As the surface of the electrode is increasingly covered by copper, the overpotential for oxygen reduction also increases, compared with the overpotential observed for a bare carbon surface. Considering the above results, the chlorine generation experiments were carried out with an ODC with 10% (wt %) copper content at an oxygen pressure of 4.0 N cm−2. 3.3. Chlorine Generation in a Two-Compartment Cell with an ODC. During the brine electrolysis experiments, the performances of three types of cathode (a pyrolytic graphite cathode, a copper-free ODC, and an ODC doped with 10% copper) were compared using a constant current density of 2470 A m−2 at temperatures of 25 and 70 °C. Figure 5 shows

Figure 6. Chlorine-evolution-reaction current response during a linear potential scan on a DSA-type electrode in a 250 g L−1 solution of NaCl, pH 3.0, for the temperatures shown. Counter electrode: pyrolytic carbon. Scan rate = 50 mV s−1.

with sodium perchlorate is a reference for comparison with the other two curves, which were obtained with a 250 g L−1 solution of NaCl at temperatures of 25 and 70 °C. As can be seen in this figure, the increase in temperature shifts the overpotential to less-positive values and causes the chlorine evolution reaction to occur earlier. Returning to Figure 5 and examining the cell/voltage curves in pairs for the same electrode material, it can be seen that the use of pyrolytic graphite resulted in the highest cell voltage for both temperatures. This was expected, because bulk graphite acts as a hydrogen-evolving cathode in membrane cells used for brine electrolysis. Bulk graphite was used in these experiments, so that the results could be compared with those obtained with an ODC. Figure 5 also shows that the cell voltage is lower for the ODC with 10% copper than for the noncatalyzed ODC. Furthermore, after 30 min of electrolysis at 70 °C, using a copper-doped ODC, it is more than 1.2 V less than the cell voltage when a pyrolytic graphite electrode is used. Figure 7 shows the results obtained during the experiments to investigate chlorine generation by brine electrolysis using a

Figure 5. Cell voltage during brine electrolysis as a function of time for a bulk pyrolytic graphite cathode, a noncatalyzed ODC and an ODC with a 10% Cu content at 25 and 70 °C. Anolyte: 250 g L−1 solution of NaCl, pH 3.0. Catholyte: 320 g L−1 solution of NaOH. O2 pressure = 4.0 N cm−2. Current density = 2470 A m−2.

plots of cell voltage as a function of electrolysis time for both temperatures for the three different types of cathode. It can be seen that temperature plays an important role in reducing the cell voltage for each electrode material used in the experiments, a finding that can be explained by the fact that higher temperatures favor the diffusion of electroactive species and reduce the overpotential for the redox reactions. This hypothesis can be confirmed by scanning the potential on a DSA-type electrode in brine solution. In the same twocompartment cell, reversing the electrodes, i.e., using the DSA as the working electrode and the ODC as the counter

Figure 7. Amount of chlorine produced by brine electrolysis at a current density of 2470 A m−2 and temperatures of 25 and 27 °C, as a function of cathode composition. Inset shows the corresponding energy consumption. 5614



Article

(2) Morimoto, T.; Suzuki, K.; Matsubara, T.; Yoshida, N. Oxygen reduction electrode in brine electrolysis. Electrochim. Acta 2000, 45, 4257−4262. (3) Moussallem, I.; Jorissen, J.; Kunz, U.; Pinnow, S.; Turek, T. Chlor-alkali electrolysis with oxygen depolarized cathodes: History, present status and future prospects. J. Appl. Electrochem. 2008, 38, 1177−1194. (4) Lipp, L.; Gottesfeld, S.; Chlistunoff, J. Peroxide formation in a zero-gap chlor-alkali cell with an oxygen-depolarized cathode. J. Appl. Electrochem. 2005, 35, 1015−1024. (5) Sugiyama, M.; Saiki, K.; Sakata, A.; Aikawa, H.; Furuya, N. Accelerated degradation testing of gas diffusion electrodes for the chlor-alkali process. J. Appl. Electrochem. 2003, 33, 929−932. (6) Siracusano, S.; Denaro, T.; Antonucci, V.; Aricò, A. S.; Urgeghe, C.; Federico, F. Degradation of oxygen-depolarized Ag-based gas diffusion electrodes for chlor-alkali cells. J. Appl. Electrochem. 2008, 38, 1637−1646. (7) Forti, J. C.; Rocha, R. S.; Lanza, M. R. V.; Bertazzoli, R. Electrochemical synthesis of hydrogen peroxide on oxygen-fed graphite/PTFE electrodes modified by 2-ethylanthraquinone. J. Electroanal. Chem. 2007, 601−6368 and references therein (8) Hamann, C. H.; Hamnett, A.; Vielstich, W. Electrochemistry;, Wiley-VCH, NY, 1998, 366. (9) Furuya, N.; Aikawa, H. Comparative study of oxygen cathodes loaded with Ag and Pt catalysts in chlor-alkali membrane cells. Electrochim. Acta 2000, 45, 4251−4256. (10) Ichinose, O.; Kawaguchi, M.; Furuya, N. Effect of silver catalyst on the activity and mechanism of a gas diffusion type oxygen cathode for chor-alkali electrolysis. J. Appl. Electrochem. 2004, 34, 55−59. (11) Wagner, N.; Schulze, M.; Gülzow, E. Long term investigations of silver cathodes for alkaline fuel cells. J. Power Sources 2004, 127, 264−272. (12) Paffett, M. T.; Beery, J. G.; Gottesfeld, S. Effects of low-levels of Co on the performance of PEM fuel-cells. J. Electrochem. Soc. 1988, 135, 1431−1435. (13) Kiros, Y.; Myren, C.; Schwartz, S.; Sampathrajan, A.; Ramanathan, M. Electrode R&D, stack design and performance of biomass-based alkaline fuel cell module. Int. J. Hydrogen Energy 1999, 24, 549−564. (14) Scherson, D.; Gupta, S. L.; Fierro, C.; Yeager, E. B.; Kordesch, M. E.; Eldridge, J.; Hoffman, R. W. Blue, Cobalt tetramethoxyphenyl porphyrin-emission Mossbauer-spectroscopy and O2 reduction electrochemical studies. Electrochim. Acta 1983, 28, 1205−1209. (15) Gojkovic, S. L.; Gupta, S.; Savinell, R. F. Heat-treated iron(III) tetramethoxyphenyl porphyrin supported on high-area carbon as an electrocatalyst for oxygen reductionI. Characterization of the electrocatalyst. J. Electrochem. Soc. 1998, 145, 3493−3499. (16) Kiros, Y.; Pirjamali, M.; Bursell, M. Oxygen reduction electrodes for electrolysis in chlor-alkalis cells. Electrochim. Acta 2006, 51, 3346− 3350. (17) Nabae, Y.; Yamanaka, I.; Otsuka, K. Electro-catalysis of the Cu/ carbon cathode for the reduction of O2 during fuel-cell reactions. Appl. Catal., A 2005, 280, 149−155. (18) Chemistry World. http://www.rsc.org/chemistryworld/News/ 2009/November/19110901.asp, accessed Feb. 17, 2013.

hydrogen-evolving pyrolytic graphite cathode and ODCs with different compositions. The amount of chlorine generated corresponds to the amount produced during 60 min after the solution had become saturated, and the data in Figure 7 are normalized by electrode area and duration of electrolysis. As can be seen, the mass of chlorine electrogenerated in the 3.1 cm2 DSA-type electrode with a current density of 2470 A m−2 does not change significantly for different cathode materials. Average values of 4.4 ± 0.8 kg m−2 h−1 and 3.3 ± 0.6 kg m−2 h−1 were obtained at 70 and 25 °C, respectively. However, a strong depolarizing effect is observed by changing the hydrogen-evolving cathode by an ODC, as can be seen in the inset of Figure 7. At 70 °C, 10% of the energy is saved in the replacement of pyrolytic graphyte by a carbon ODC. By adding copper to the ODC surface, the energy demand is reduced from 3200 kWh ton−1 to 1850 kWh ton−1 (42%) for the electrosynthesis of the same amount of chlorine. It should be noted that the energy consumption figures shown in the insert of Figure 7 should only be used to compare the performance of the electrodes tested in this study. Although membrane cells, particularly those with an ODC, provide energy savings, the potential drops in laboratory-scale cells are different. As already mentioned, the ohmic drop and its minimization were not taken into consideration in the design of the electrolysis cell used in this study, and the anode/cathode distance in the cell was 11 cm which resulted in a cell voltage of ∼4.0 V. Literature reports results obtained during operation of ODC cells with values between 2.0 V and 2.2 V at higher current densities than those employed in the present study.2−4 Furthermore, the present energy demand for modern membrane processes with hydrogen-evolving cathodes is ∼2000 kWh ton−1, and cell voltage in the Bayer ODC process is below 2 V.18 In the present study, the energy demand was 1850 kWh ton−1 at 1470 A m−2 (cell voltage of 4 V) with the Cu−C−ODC. However, the ohmic drop can be reduced, and also the energy consumption, if those variables that minimize the ohmic drop are taken into consideration in the cell design, which has been the subject of ongoing studies in our group.

4. CONCLUSIONS Replacement of the hydrogen-evolution reaction by the oxygenreduction reaction in membrane cells used to produce chlorine provides significant energy savings. The use of an oxygen-fed ODC not only overcomes the problem of the low solubility of oxygen in aqueous solutions, but also allows the gas flow rate to be chosen so as to avoid mass-transfer limitation of the reaction rate. The addition of copper to the ODC further depolarizes the overall reaction in such a way as to increase chlorine production and reduce energy demand. Comparison of the results using a graphite (hydrogen-evolving) cathode and a copper-doped cathode at 70 °C showed that the latter resulted in a 42% reduction in energy demand.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) World Chlorine Council. http://www.worldchlorine.org/about/ index.html, accessed Sept. 14, 2012. 5615


PTFE Oxygen-Depolarized Cathodes for Chlor-alkali

Recommend Documents