Platinum/vivianite bifunction catalysts for DMFC

Bi-functional catalysts are used to solve the poisoning problem caused by carbon monoxide (CO) which is the intermediate of direct methanol fuel cells (DMFCs). Flower-like vivianite (Fe₃(PO₄)₂·8H₂O) spheres with diameter around 10 μm are originally used as supports of Pt to form bifunction catalysts. The cyclic voltammetry in 1 M H₂SO₄ indicates that the electrochemical surface area (ECSA) of Pt reduced on as-prepared vivianite (Pt/Vi) was 105, greater than 91 m² g⁻¹ for the commercial Pt/C. Besides, Pt/Vi reveals the less CO poisoning effects, including the greater mass activity in methanol oxidation and the lower onset potential in CO-stripping than Pt/C. These excellent performances on electrolyzes are related to the chemical state of Fe³⁺ and the coexistence of Pt⁰ and Pt²⁺ in Pt/Vi. The former activates the water and yields Fe-OH_ads at lower potential and the latter may offer an easy way of electron transition.     

Preparation and characterization of Pt nanoparticles supported on a Fe-doped hydroxyapatite-activated Vulcan XC72 composite material

In this research, the hydroxyapatite (HAp) could be directly deposited on carbon black (CB), which was the modified surface to generate more OH⁻ free radicals to strengthen the bond between HAp and CB, before adding ((NH₄)₂Fe(SO₄)₂·6H₂O) to engage the ion exchange with Fe²⁺ and Ca²⁺ to obtain FeHAp-CB composites. The Pt nanoparticles were then reduced on the FeHAp-CB composite surface to derive a Pt/FeHAp-CB catalyst of dual function. The catalyst revealed a steep desorption peak at −0.180 V (vs Ag/AgCl) in a hydrogen oxidation reaction ascribed to the characteristics of Pt (110) facet and the CO detoxication function in the methanol oxidation reaction. The superior performance of Pt/FeHAp-CB/CB catalyst was apparently related to the Pt (110) surface, the Fe concentration, and the homogeneous dispersion of Pt particles on the FeHAp-CB composites. And, the ratio of coexisting Pt⁰ and Pt²⁺ within Pt/FeHAp-CB/CB catalyst would definitely affect chemical stability and mass activity. By X-ray photoelectron spectroscopy (XPS), it was found that a high quantity of Pt⁰ could improve mass activity, while a high quantity of Pt²⁺ contributed to chemical stability.     

Application of N-doped carbon nanotube-supported Pt-Ru as electrocatalyst layer in passive direct methanol fuel cell

In this research, nitrogen-doped carbon nanotubes (N-CNT) were prepared through the low-temperature thermal method and used as the support material for the bimetallic catalyst PtRu and Pt nanoparticles. A passive single-cell direct methanol fuel cell (DMFC) was designed and fabricated to investigate and compare the performance of three discrete membrane electrode assemblies (MEA) with carbon black (CB), CNT, and N-CNT as the catalyst support, respectively. Adding N to the structure of CNTs remarkably improves the physical and electrochemical characteristics of the catalyst. More active sites and stronger interaction between support and metal particles lead to the formation of smaller metal clusters and higher surface area as well as superior electrochemical activity. Compared to PtRu/CB and PtRu/CNT, PtRu/N-CNT illustrate 32% and 12% higher surface area, 3 and 1.9 times higher MOR activity, and 62% and 18% higher power output (26.1 mW/cm²), respectively. Moreover, it is revealed that PtRu/N-CNT has long-term stability in the MOR. The research work presented in this paper exhibits the outstanding performance of Pt and PtRu supported on N-CNT in a passive single-cell DMFC.     

Methanol oxidation reaction activity of microwave-irradiated and heat-treated Pt/Co and Pt/Ni nano-electrocatalysts

Bimetallic Pt nanoparticles were prepared by alloying Pt with the non-noble transition metals, Co and Ni, using a conventional heat-treatment (HT) method and microwave-irradiation (MW). The resulting samples were Pt–Co-Ht, Pt–Ni-HT, Pt–Co, MW and Pt–Ni-MW. The aim was to evaluate the electrocatalytic behaviour and surface properties of the materials based on the alloying metal used and the synthesis process. XRD studies of the nanoparticles indicated that alloyed structures were formed for the microwave (MW) synthesized samples, as seen by a decrease in the lattice parameters. Using X-ray photoelectron spectroscopy analysis, surface segregation of Co and Ni occurred (1:4 surface atomic ratio Pt–Co or Ni) for the Pt–Co-MW and Pt–Ni-MW samples. In contrast the heat-treated Pt–Ni catalyst showed Pt surface segregation. Methanol oxidation reaction (MOR) studies revealed an increase in the electrocatalytic activity upon the addition of Co and Ni to Pt when compared to a monometallic Pt catalyst. The presence of oxide and hydroxide alloying metal species is suggested to be the cause of the observed enhancement in the catalytic activity. Overall the Pt–Ni-MW catalyst displayed the best MOR activity and this is attributed to the large amounts of Ni-hydroxide species observed on the catalyst surface.     

Electrochemical and capacitive properties of thin-layer carbon black electrodes

Electrochemical properties and porous-structure-dependent capacitive ability of commercial carbon blacks, Black Pearls 2000^® (BP) and Vulcan^® XC 72R (XC), were investigated in H₂SO₄ solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The capacitance in-depth profile is correlated to microscopic appearance of carbon blacks in the form of a thin layer applied over Au substrate from water suspensions of BP and XC. The capacitance calculated from voltammetric charge was found to depend on the sweep rate, due to porosity of investigated materials. Impedance (EIS) characteristics upon frequency-dependent charge/discharge process indicate transmission line electric behavior of BP and XC. Capacitance and resistance values obtained by simulations of EIS data, enabled estimation of capacitance and resistance profile throughout carbon black porous electrodes. Capacitance of BP carbon layer increases going from the outer surface towards the bulk of the layer. External capacitance originates from capacitive characteristics of the macroscopic surface consisting of relatively large agglomerates, while internal capacitance originates from “inner” surface of micro-porous agglomerates. Contrary to BP, opposite distribution of the total capacitance to external and internal part was found for XC, caused by its loose structure and considerably lower real surface area in comparison to BP. The XC morphology makes additionally the pseudocapacitive contribution of surface functionalities more pronounced, which indirectly shifts also the “internal” double-layer capacitive response to higher frequencies through the effect of increased wettability of the layer. Thus, the capacitance of XC surface directly exposed to the electrolyte is larger than that of the inner one, which makes it a “fully-utilized” capacitor, while increased capacitive performance of BP emerges only at very low frequencies of charging/discharging process.     

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H₂PtCl₆ as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m² g⁻¹) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g⁻¹) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g⁻¹) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g⁻¹). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.     

In situ ion exchange preparation of Pt/carbon nanotubes electrode: Effect of two-step oxidation of carbon nanotubes

The in situ ion exchange method has been employed to prepare carbon nanotubes (CNT) supported Pt electrode, in which CNT is functionalized with two-step oxidation, namely electrochemical oxidation and chemical oxidation. X-ray photoelectron spectroscopy (XPS) confirms that two-step oxidation produces more carboxylic acid groups. Transmission electron microscopy (TEM) shows that Pt nanoparticles are highly dispersed on the CNT surface. Electrochemical measurements show that the resultant Pt/CNT electrode treated by two-step oxidation exhibits the largest electrochemical surface area and the highest activity for oxygen reduction reaction (ORR) among the investigated electrodes. This can be attributed to the fact that the two-step oxidation treatment produces more carboxylic acid groups which is the determining factor for Pt loading and dispersion via ion-exchange.     

Preparation of iron and nitrogen co-doped carbon material Fe/N-CCM-T for oxygen reduction reaction

In this paper, iron and nitrogen co-doped carbon material with nanotube structure (Fe/N-C_CM-T) was synthesized by pyrolyzing a mixture of Fe salt, chitosan and melamine and displayed high electrocatalytic performance for oxygen reduction reaction (ORR). The structure of the Fe/N-C_CM-T was characterized and their ORR performance in alkaline media was investigated by linear sweep voltammetry, cyclic voltammetry and chronoamperometry. Fe/N-C_CM-T displayed better ORR performance than other carbon materials like Fe/N-C_C-800. The Fe/N-C_CM-800 with a large surface area (302.5 m²/g) especially exhibited the best ORR electrocatalytic performance among the prepared carbon materials, which was also proved by its similar Tafel slope (76 mV decade^?1) to Pt/C catalyst (74 mV decade^?1). Fe/N-C_CM-800 showed similar ORR activity as commercial Pt/C catalyst, but superior tolerance to methanol and stability. Such high ORR performance of the Fe/N-C_CM-T can be attributed to its nanotube structure, high specific surface area (SSA), high graphitic-N and pyridinic-N contents.     

Preparation and physical/electrochemical characterization of Pt/poly(vinylferrocenium) electrocatalyst for methanol oxidation

Preparation and characterization of a platinum (Pt)-based catalyst using a redox polymer, poly(vinylferrocenium) (PVF⁺), as the support material was described. Pt was obtained from aqueous solution of K₂PtCl₄ in the complex form. Pt particles were reduced by chemical and electrochemical means. Chemical reduction was performed using aqueous hydrazine solution and electrochemical reduction was carried out in H₂SO₄ solution. The Pt/PVF⁺ catalyst system showed catalytic activity towards methanol oxidation. Cyclic voltammetry was used for the electrochemical characterization of the catalyst system. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectrum (EDS) of the catalyst system were also recorded. The system was tested in a single fuel cell configuration at ambient temperature and atmospheric pressure. The open circuit voltage (OCV) was 680 mV for the system and the maximum power density was 0.31 mW cm⁻² at a current density of 0.63 mA cm⁻². Catalytic activity of Pt/PVF⁺ system towards methanol oxidation was comparable with the related catalysts in the literature.     

Impact of anode catalyst loadings and carbon supports to CO contamination in PEM fuel cells

Hydrogen fuel quality is important for the successful commercialization of PEM (proton exchange membrane) fuel cell vehicles (FCVs) because impurities can adversely affect the normal operation of FCVs both immediately and during their lifetime operation. Among the impurities specified in H₂ quality standards, CO (carbon monoxide) is known to have one of the greatest impacts on fuel cells because of the immediate decrease in performance at low concentrations. CO impurity levels of only 0.2 ppm, as specified in the H₂ quality standards, were found in H₂ refueling stations with adverse impacts to PEM fuel cell operation. In this study CO impurity testing was conducted on single cells based on an extensive design of experiments (DOE) that was performed using several MEAs with two levels of anode platinum loading (0.05 mg_Pt/cm² and 0.1 mg_Pt/cm²) and two different materials for platinum carbon support (Highly Graphitized Carbon and High Surface Area Carbon). Contamination testing for each MEA design configuration was performed at four different CO impurity levels (0.1 ppm, 0.2 ppm, 0.3 ppm, and 0.4 ppm) and three current densities (0.1 A/cm², 1.0 A/cm², and 1.7 A/cm²) at each impurity level. The results indicate that the most significant factor to improve MEA tolerance to CO contamination was the choice of carbon support. The use of high surface area carbon had an even greater impact than the use of higher Pt loading, which suggests paths toward addressing CO contamination that avoid higher catalyst cost.     

Effects of carbon coating and iron phosphides on the electrochemical properties of LiFePO4/C

Carbon coated LiFePO₄ (LiFePO₄/C) with different contents of high electron conductive iron phosphide phase was synthesized by an aqueous sol–gel method in a reductive sintering atmosphere. Different synthesis parameters were used for adjusting the microstructure and phase compositions of the products. The effects of the carbon coating and iron phosphides on the electrochemical properties of the LiFePO₄/C electrodes were studied by means of testing the discharge capacities at rates of 0.1–5C (1C = 170 mAh g⁻¹) and analyzing the CV curves. The results show that carbon coating in a content of 1.5 wt.% derived from the carbon source of ethylene glycol greatly decreases the particle size of LiFePO₄ in one order in the specific surface area, and significantly improves the rate capability of LiFePO₄. The effect of the content of FeP on the capacity of the carbon coated LiFePO₄ was different at different discharge rates. Increasing the content of FeP from 1.2 to 3.7 wt.% slightly decreases the capacity of LiFePO₄/C at low discharge rate (0.1C and 1C), but obviously increases the capacity of LiFePO₄/C when the discharge rate is increased to 5C. For the carbon free sample, even it also has 1.8 wt.% FeP, it still possesses poor capacity due to the large particle size of LiFePO₄ and the lack of conductivity. And too much iron phosphides lowers the discharge capacity of the electrode since they are inert for the deinsertion/insertion of lithium ion.     

Preparation and performance characterization of the Fe–Ni/ScSZ cermet anode for oxidation of ethanol fuel in SOFCs

An anodic cermet of Fe–Ni alloy and scandia stabilized zirconia (ScSZ) has been investigated for a solid oxide fuel cell (SOFC) running on ethanol fuel. Composite anodes having alloy compositions of 0, 12.5, 25, 37.5, 50 and 100 wt.% Ni were exposed to ethanol stream at 700 °C for 12 h to demonstrate that carbon formation is greatly suppressed on the Fe–Ni alloys compared to that of pure Ni. Then the short-term stability for the cells with the Ni/ScSZ and Fe_0.5Ni_0.5/ScSZ anodes in ethanol stream at 700 °C was checked over a relative long period of operation. Open circuit voltages (OCVs) increased from 1.03 to 1.1 V, and power densities increased from 120 to 460 mW cm² as the operating temperature of a SOFC with Fe_0.5Ni_0.5/ScSZ anode was increased from 700 to 850 °C in ethanol stream. Electrochemical impedance spectra (EIS) illustrated that the cell with Ni/ScSZ anode exhibits slightly less total impedance than that observed for the cell with Fe_0.5Ni_0.5/ScSZ anode. The performance of a fuel cell made with the Ni/ScSZ and Fe_0.5Ni_0.5/ScSZ anodes was tested in ethanol stream for 48 h and showed a significant decrease in polarization resistance with time. Impedance spectra of similar fuel cells suggest that small carbon deposits are formed with time and that the decrease in polarization resistance is due to enhanced electronic conductivity in the anode.     

Carbon paper supported Pt/Au catalysts prepared via Cu underpotential deposition-redox replacement and investigation of their electrocatalytic activity for methanol oxidation and oxygen reduction reactions

Through a simple and rapid method, carbon papers (CPs) were coated with Au and the resulting Au/CP substrates were used for the preparation of Pt/Au/CP by Cu underpotential deposition (Cu UPD) and redox replacement technique. A series of Pt_n/Au/CP catalysts (where n = number of UPD-redox replacement cycles) were synthesized and their electrochemical properties for methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were investigated by electrochemical measurements. The Pt_n/Au/CP electrodes show higher electrocatalytic activity and enhanced poison tolerance for the MOR as compared to a commercial Pt/C on CP (Pt/C/CP). The highest mass specific activity and Pt utilization efficiency for MOR was observed on Pt₁/Au/CP with a thickness close to a monatomic Pt layer. Chronoamperometric tests in methanol solution revealed that Pt_n/Au/CPs have much higher CO tolerance compared to Pt/C/CP. Among the Pt_n/Au/CPs, CO tolerance decreases with increasing the amount of deposited Pt, indicating that the exposed Au atoms in close proximity to Pt plays a positive role against CO poisoning. Compared with the Pt/C/CP, all the Pt_n/Au/CP electrodes show more positive onset potentials and lower overpotentials for ORR. For instance, the onset potential of ORR is 150 mV more positive and the overpotential is ∼140 mV lower on Pt₄/Au/CP with respect to Pt/C/CP.     

Characterization of Pt supported on commercial fluorinated carbon as cathode catalysts for Polymer Electrolyte Membrane Fuel Cell

Pt nanoparticles supported on carbon monofluoride (CFx), synthesized from H₂PtCl₆ using NaHB₄ as a reducing agent has been investigated as a cathode electrocatalyst in fuel cells. Surface characterization, performed by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD), shows a homogeneous distribution and high dispersion of metal particles. Kinetic parameters for the electrocatalyst are also obtained from the steady state measurements using a rotating disk electrode (RDE) in 0.5 M H₂SO₄ solution. Analysis by Koutecky–Levich equation indicates an overall 4 e^? oxygen reduction reaction (ORR). Evaluation of the catalyst in single cell membrane electrode assemblies (MEAs) for proton exchange membrane based Direct Methanol Fuel Cell (DMFC) and H₂ Fuel Cell at different temperatures and flows of O₂ and Air are shown and compared against commercial Pt/C as the cathode electrocatalyst. Evaluation of Pt/CFx in H₂ fed fuel cells shows a comparable performance against a commercial catalyst having a higher platinum loading. However, in direct methanol fuel cell cathodes, an improved performance is observed at low O₂ and air flows showing up to 60–70% increase in the peak power density at very low flows (60 mL min^?1).     

In and ex situ characterization of an anion-exchange membrane for alkaline direct methanol fuel cell (ADMFC)

Anion exchange membrane fumasep^® FAA-2 was characterized with ex and in situ methods in order to estimate the membranes’ suitability as an electrolyte for an alkaline direct methanol fuel cell (ADMFC). The interactions of this membrane with water, hydroxyl ions and methanol were studied with both calorimetry and NMR and compared with the widely used proton exchange membrane Nafion^® 115. The results indicate that FAA-2 has a tighter structure and more homogeneous distribution of ionic groups in contrast to the clustered structure of Nafion, moreover, the diffusion of OH⁻ ions through this membrane is clearly slower compared to water molecules. The permeability of methanol through the FAA-2 membrane was found to be an order of magnitude lower than for Nafion. Fuel cell experiments in 1 mol dm⁻³ methanol with FAA-2 resulted in OCV of 0.58 V and maximum power density of 0.32 mW cm⁻². However, even higher current densities were obtained with highly concentrated fuels. This implies that less water is needed for fuel dilution, thereby decreasing the mass of the fuel cell system. In addition, electrochemical impedance spectroscopy for the ADMFC was used to determine ohmic resistance of the cell facilitating the further membrane development.     

Preparation and characterization of Ni based catalysts for the catalytic partial oxidation of methane: Effect of support basicity on H2/CO ratio and carbon deposition

The catalytic partial oxidation of methane (CPOM) was studied on Ni based catalysts. Catalysts were prepared by wet impregnation method and characterized by using AAS, BET, XRD, HRTEM, TPR, TPO, Raman Spectroscopy and TPSR techniques. The prepared catalysts showed nearly 95% CH₄ conversion and nearly 96% H₂ selectivity under the flow of 157,500 (L kg⁻¹ h⁻¹) with the ratio of CH₄/O₂ = 2 by using air as an oxidant at 1 atm and 800 °C. Support basicity greatly influenced the H₂/CO ratio and carbon deposition. It was found that the lowest carbon deposition occurred on Ni impregnated MgO catalyst. Considering the results, it was found that Ni/MgO catalyst with 10% Ni content would be the best catalyst amongst Ni/Al₂O₃, Ni/MgO/Al₂O₃, Ni/MgAl₂O₄ and Ni/Sorbacid for the CPOM only under more reductive conditions. Under optimum conditions, Ni/MgO showed poor performance and therefore Ni/Sorbacid would be the ideal catalyst because of its greater carbon resistance than the other catalysts.     

Preparation and study of electrocatalytic activity of Ni-Pd(OH)2/C nanocomposite for hydrogen evolution reaction in alkaline solution

A new catalyst (Ni-Pd(OH)₂/C) for hydrogen evolution reaction (HER) was prepared by coelectrodeposition of Pd(OH)₂/C nanoparticles and Ni on a Cu substrate in two steps. Furthermore, the effect of Mo ions in alkaline solution (1 M NaOH) on the electrocatalytic activity of Ni-Pd(OH)₂/C nanocomposite was studied as an in-situ activator for the HER. The various electrochemical methods were employed to study the HER activity of the investigated new catalyst, including linear sweep voltammetry (LSV), the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The electrochemical measurements showed that the Ni-Pd(OH)₂/C nanocomposite as a catalyst for the HER has an excellent catalytic activity with good stability in alkaline solution. Furthermore, the rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated using Tafel-impedance data and revealed that the proton discharge electrosorption or Volmer reaction (k₁= (6.8 ± 0.7) × 10⁻⁸ mol cm⁻² s⁻¹) was the rate determining step (RDS) of the HER on the surface of Ni-Pd(OH)₂/C nanocomposite. Also, it was observed that the presence of Mo ions in alkaline solution could significantly increase the HER activity of Ni-Pd(OH)₂/C nanocomposite. The comparison of RDS rate constant value with surface roughness (R_f) of Ni-Pd(OH)₂/C catalyst showed that its high activity toward the HER originated from both increase in the surface roughness (∼20%) and increase in synergistic effect (∼80%).     

Fuel saving, carbon dioxide emission avoidance, and syngas production by tri-reforming of flue gases from coal- and gas-fired power stations, and by the carbothermic reduction of iron oxide

Flue gases from coal, gas, or oil-fired power stations, as well as from several heavy industries, such as the production of iron, lime and cement, are major anthropogenic sources of global CO₂ emissions. The newly proposed process for syngas production based on the tri-reforming of such flue gases with natural gas could be an important route for CO₂ emission avoidance. In addition, by combining the carbothermic reduction of iron oxide with the partial oxidation of the carbon source, an overall thermoneutral process can be designed for the co-production of iron and syngas rich in CO. Water-gas shift (WGS) of CO to H₂ enables the production of useful syngas. The reaction process heat, or the conditions for thermoneutrality, are derived by thermochemical equilibrium calculations. The thermodynamic constraints are determined for the production of syngas suitable for methanol, hydrogen, or ammonia synthesis. The environmental and economic consequences are assessed for large-scale commercial production of these chemical commodities. Preliminary evaluations with natural gas, coke, or coal as carbon source indicate that such combined processes should be economically competitive, as well as promising significant fuel saving and CO₂ emission avoidance. The production of ammonia in the above processes seems particularly attractive, as it consumes the nitrogen in the flue gases.     

Preparation and properties of carbon nanotube-reinforced vinyl ester/nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

Novel multiwalled carbon nanotubes (MWNTs) were prepared using poly(oxypropylene)-backboned diamines of molecular weights M_w 400 and 2000 to disperse acid-treated MWNTs, improving the performance of composite bipolar plates in polymer electrolyte membrane fuel cells. A lightweight polymer composite bipolar plate that contained vinyl ester resin, graphite powder and MWNTs was fabricated using a bulk molding compound (BMC) process. Results demonstrate that the qualitative dispersion of MWNTs crucially determined the resultant bulk electrical conductivity, the mechanical properties and the physical properties of bipolar plates. The flexural strength of the composite bipolar plate with 1 phr of MWNTs was approximately 48% higher than that of the original composite bipolar plate. The coefficient of thermal expansion of the composite bipolar plate was reduced from 37.00 to 20.40 μm m⁻¹ °C⁻¹ by adding 1 phr of MWNTs, suggesting that the composite bipolar plate has excellent thermal stability. The porosity of the composite bipolar plate was also evaluated. Additionally, the bulk electrical conductivity of the composite bipolar plate with different MWNTs types and contents exceeds 100 S cm⁻¹. The results of the polarization curves confirm that the addition of MWNTs leads to a significant improvement on the single cell performance.