Conducting carbon/polymer composites as a catalyst support for proton exchange membrane fuel cells

Carbon/poly(3,4‐ethylene dioxythiophene) (C/PEDOT) composites are synthesized by in situ chemical oxidative polymerization of EDOT monomer on carbon black in order to decrease carbon corrosion that occurred in carbon‐supported catalysts used in proton exchange membrane fuel cell. The effects of different dopants including polystyrene sulfonic acid, p‐toluenesulfonic acid and camphorsulfonic acid with the addition of ethylene glycol or dimethyl sulfoxide on the properties of the composites are investigated. The synthesized composites are characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, surface area analysis and scanning electron microscope. Electrical conductivity is determined by using the four‐point probe technique. Electrochemical oxidation characteristics of the synthesized C/PEDOT composites are investigated by cyclic voltammetry by applying 1.2 V for 24 h. The composite prepared at 25 °C with p‐toluenesulfonic acid and ethylene glycol shows the best carbon corrosion resistance. Platinum‐supported catalyst by using this composite was prepared using microwave irradiation technique, and it was seen that the prepared catalyst did not significantly lose its hydrogen oxidation and oxygen reduction reaction activities after electrochemical oxidation. Copyright © 2013 John Wiley & Sons, Ltd.     

Nanostructured polypyrrole/carbon composite as Pt catalyst support for fuel cell applications

A novel catalyst support was synthesized by in situ chemical oxidative polymerization of pyrrole on Vulcan XC-72 carbon in naphthalene sulfonic acid (NSA) solution containing ammonium persulfate as oxidant at room temperature. Pt nanoparticles with 3–4 nm size were deposited on the prepared polypyrrole–carbon composites by chemical reduction method. Scanning electron microscopy and transmission electron microscopy measurements showed that Pt particles were homogeneously dispersed in polypyrrole–carbon composites. The Pt nanoparticles-dispersed catalyst composites were used as anodes of fuel cells for hydrogen and methanol oxidation. Cyclic voltammetry measurements of hydrogen and methanol oxidation showed that Pt nanoparticles deposited on polypyrrole–carbon with NSA as dopant exhibit better catalytic activity than those on plain carbon. This result might be due to the higher electrochemically available surface areas, electronic conductivity and easier charge-transfer at polymer/carbon particle interfaces allowing a high dispersion and utilization of deposited Pt nanoparticles.     

Synthesis of polypyrrole (PPy) based porous N-doped carbon nanotubes (N-CNTs) as catalyst support for PEM fuel cells

In this study, it was aimed to synthesize catalytically active, high surface area carbon nanotubes (CNTs) by means of nitrogen doping (N-doping). The synthesized nitrogen doped carbon nanotubes (N-CNTs) were used as Pt catalyst support in order to improve oxygen reduction reaction (ORR) kinetics at the cathode electrode in PEM fuel cell. Polypyrrole (PPy) was served as both carbon and nitrogen source and FeCl₃ solution was used as oxidizing agent in the synthesis procedure of N-CNTs. Chemical activation of the materials was made with potassium hydroxide (KOH) solution during 12 and 18 h time periods. It was considered that activation period is of great importance on the properties of the synthesized PPy based N-CNTs. 12 h activated N-CNTs gave higher surface area (1607.2 m²/g) and smaller micropore volume (0.355 cm³/g) in comparison to 18 h activated N-CNTs having smaller surface area (1170.7 m²/g) and higher micropore volume (0.383 cm³/g). PEM fuel cell performance results showed that 12 h activated N-CNTs are better catalyst supports than 18 h activated N-CNTs for Pt nanoparticle decoration.     

Polypyrrole/carbon black composite as a novel oxygen reduction catalyst for microbial fuel cells

A polypyrrole/carbon black (Ppy/C) composite has been employed as an electrocatalyst for the oxygen reduction reaction (ORR) in an air-cathode microbial fuel cell (MFC). The electrocatalytic activity of the Ppy/C is evaluated toward the oxygen reduction using cyclic voltammogram and linear sweep voltammogram methods. In comparison with that at the carbon black electrode, the peak potential of the ORR at the Pp/C electrode shifts by approximate 260 mV towards positive potential, demonstrating the electrocatalytic activity of Ppy toward ORR. Additionally, the results of the MFC experiments show that the Ppy/C is well suitable to fully substitute the traditional cathode materials in MFCs. The maximum power density of 401.8 mW m⁻² obtained from the MFC with a Ppy/C cathode is higher than that of 90.9 mW m⁻² with a carbon black cathode and 336.6 mW m⁻² with a non-pyrolysed FePc cathode. Although the power output with a Ppy/C cathode is lower than that with a commercial Pt cathode, the power per cost of a Ppy/C cathode is 15 times greater than that of a Pt cathode. Thus, the Ppy/C can be a good alternative to Pt in MFCs due to the economic advantage.     

Graphitic mesoporous carbon as a durable fuel cell catalyst support

Highly stable graphitic mesoporous carbons (GMPCs) are synthesized by heat-treating polymer-templated mesoporous carbon (MPC) at 2600 °C. The electrochemical durability of GMPC as Pt catalyst support (Pt/GMPC) is compared with that of carbon black (Pt/XC-72). Comparisons are made using potentiostatic and cyclic voltammetric techniques on the respective specimens under conditions simulating the cathode environment of PEMFC (proton exchange membrane fuel cell). The results indicate that the Pt/GMPC is much more stable than Pt/XC-72, with 96% lower corrosion current. The Pt/GMPC also exhibits a greatly reduced loss of catalytic surface area: 14% for Pt/GMPC vs. 39% for Pt/XC-72.     

Use of cellulose-based carbon aerogels as catalyst support for PEM fuel cell electrodes: Electrochemical characterization

New nanostructured carbons have been developed through pyrolysis of organic aerogels, based on supercritical drying of cellulose acetate gels. These cellulose acetate-based carbon aerogels (CA) are activated by CO₂ at 800 °C and impregnated by PtCl₆²⁻; the platinum salt is then chemically or electrochemically reduced. The resulting platinized carbon aerogels (Pt/CA) are characterized with transmission electron microscopy (TEM) and electrochemistry. The active area of platinum is estimated from hydrogen adsorption/desorption or CO-stripping voltammetry: it is possible to deposit platinum nanoparticles onto the cellulose acetate-based carbon aerogel surface in significant proportions. The oxygen reduction reaction (ORR) kinetic parameters of the Pt/CA materials, determined from quasi-steady-state voltammetry, are comparable with that of Pt/Vulcan XC72R. These cellulose acetate-based carbon aerogels are thus promising electrocatalyst support for PEM application.     

Bipolar plates made of plain weave carbon/epoxy composite for proton exchange membrane fuel cell

Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell (PEMFC) is composed of bipolar plates, end plates, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs). Among the constituents of PEMFCs, the bipolar plate is a key component that collects and conducts the current from cell to cell. The electrical resistance of the bipolar plate, which consists of the bulk material resistance and interfacial contact resistance between the GDLs and the bipolar plates, should be reduced to improve the performance of the fuel cell.     

Polypyrrole-modified hydrophobic carbon nanotubes as promising electrocatalyst supports in polymer electrolyte membrane fuel cells

As an alternative to oxidative acid treatment, a hydrophobic graphitized carbon nanotube (CNT) was functionalized with 1-4 nm thick polypyrrole (PPy) prior to application as catalyst supports in polymer electrolyte membrane (PEM) fuel cells. Unlike oxidative acid treatment, the PPy coating method converts the hydrophobic surface of a CNT to a hydrophilic one without creating defects on the surface of the CNT. As a result, Pt nanoparticles deposited on the PPy-coated CNTs showed an improved distribution, which significantly enhanced the fuel cell performance while preserving the intrinsic properties of the CNTs, i.e., resistance to electrochemical carbon corrosion. An additional advantage of PPy coating is that it prevents Pt nanoparticles from agglomerating on the CNT surface. These results indicated that PPy-coated CNTs are a promising catalyst support to improve both the performance and durability of PEM fuel cells.     

Utilization of the graphene aerogel as PEM fuel cell catalyst support: Effect of polypyrrole (PPy) and polydimethylsiloxane (PDMS) addition

In this study, three-dimensional (3D) graphene aerogel (GA) was synthesized by a self-assembly hydrothermal process as a PEM fuel cell catalyst support. The synthesized GA was also modified with the polypyrrole (PPy) by in-situ chemical oxidative polymerization of the pyrrole monomer (PPy-GA). The electrocatalytic performance of the platinum (Pt) nanoparticles (NPs) supported with both GA and PPy-GA materials towards oxygen reduction reaction (ORR) was investigated. In addition, the hydrophobic polydimethylsiloxane (PDMS) polymer was added to the catalyst ink media in order to enhance the hydrophobic property and durability of the synthesized GA and PPy-GA supported Pt catalysts. Pt NPs were decorated over the support materials with the microwave irradiation technique. Various characterization techniques such as FTIR, Raman Spectroscopy, BET, SEM, EDX, TEM, TGA, contact angle measurements, 3D topography images and four-point probe electrical conductivity measurements were performed in order to analyze the GA based support materials. Electrochemical characterizations were also carried out with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. It was observed that PDMS addition to the catalyst ink media increased the electrocatalytic activity and durability of the GA supported Pt catalyst. Otherwise, the performance of the PPy modified GA supported Pt catalyst was negatively affected by the addition of PDMS to the catalyst media.     

Carbon nanofibers as electrocatalyst support for fuel cells: Effect of hydrogen on their properties in CH4 decomposition

The influence of low partial pressure of hydrogen on carbon nanofibers (CNFs) properties has been studied in the synthesis by methane catalytic decomposition, with the purpose of using them in polymer electrolyte fuel cells as electrocatalyst support. Using CNFs in this kind of application presents a good perspective to improve the fuel cell overall performance. CNF growth in the catalytic decomposition of methane and the characteristics which are typically required in a carbonaceous support, are influenced by hydrogen concentration, which has been studied at different temperatures. The textural, morphological and structural characteristics of the obtained CNFs have been determined by nitrogen physisorption, X-ray diffraction, electron microscopy and thermogravimetry. Electrical conductivity of CNFs has been measured compressing the powder and using a two-probe method. It was observed that low values of partial pressure of hydrogen in methane influence positively structural ordering of CNFs, and in turn improve electrical conductivity, with a slight influence on textural properties leading to highly mesoporous carbon.     

Polyaniline and polypyrrole coatings on aluminum for PEM fuel cell bipolar plates

The conducting polymers polypyrrole and polyaniline were deposited on 6061 aluminum using cyclic voltammetry and painting, respectively. These samples are intended for proton exchange membrane fuel cell applications where surface contact resistance as well as bulk corrosion resistance are requirements for the bipolar plates that separate the cells. Corrosion current and voltage were measured on the samples as well as contact resistance between coated samples as a function of contact pressure. The polypyrrole samples showed neither improved corrosion resistance nor acceptable contact resistance. The painted polyaniline samples, however, showed about an order of magnitude reduction in corrosion current with only a minor increase in contact resistance. It is believed that in the more acidic environment of a fuel cell, the polyaniline will become even more conductive and that further reduction in contact resistance should be possible.     

Effect of carbon black support corrosion on the durability of Pt/C catalyst

The work intends to clarify the effect of carbon black support corrosion on the stability of Pt/C catalyst. The corrosion investigations of carbon blacks with similar structures and characteristics were analyzed by cyclic voltammograms (CV) and X-ray photoelectron spectroscopy (XPS). The results indicate that a higher oxidation degree appears on the Black Pearl 2000 (BP-2000) support, i.e. BP-2000 has a lower corrosion resistance than Vulcan XC-72 (XC-72). The durability investigation of Pt supported on the two carbon blacks was evaluated by a potential cycling test between 0.6 and 1.2 V versus reversible hydrogen electrode (RHE). A higher performance loss was observed on the Pt/BP-2000 gas diffusion electrode (GDE), compared with that of Pt/XC-72. XPS analysis suggests that higher Pt amount loss appeared in the Pt/BP-2000 GDE after durability test. X-ray diffraction (XRD) analysis also shows that Pt/BP-2000 catalyst presents a higher Pt size growth. The higher performance degradation of Pt/BP-2000 is attributed significantly to the less support corrosion resistance of BP-2000.     

Investigation of the effect of graphitized carbon nanotube catalyst support for high temperature PEM fuel cells

In this study, it is aimed to investigate the graphitization effect on the performance of the multi walled carbon nanotube catalyst support for high temperature proton exchange membrane fuel cell (HT-PEMFC) application. Microwave synthesis method was selected to load Pt nanoparticles on both CNT materials. Prepared catalyst was analyzed thermal analysis (TGA), Transmission Electron Microscopy (TEM) and corrosion tests. TEM analysis proved that a distribution of Pt nanoparticles with a size range of 2.8–3.1 nm was loaded on the Pt/CNT and Pt/GCNT catalysts. Gas diffusion electrodes (GDE) were manufactured by an ultrasonic spray method with synthesized catalyst. Polybenzimidazole (PBI) membrane based Membrane Electrode Assembly (MEA) was prepared for observe the performance of the prepared catalysts. The synthesized catalysts were also tested in a HT-PEMFC environment with a 5 cm² active area at 160 °C without humidification. This study demonstrates the feasibility of using the microwave synthesis method as a fast and effective method for preparing high performance Pt/CNT and Pt/GCNT catalyst for HT-PEMFC. The HT-PEMFC performance evaluation shows current densities of 0.36 A/cm²0.30 A/cm² and 0.20 A/cm² for the MEAs prepared with Pt/GCNT, Pt/CNT and Pt/C catalysts @ 0.6 V operating voltage, respectively. AST (Accelerated Stress Test) analyzes of MEAs prepared with Pt/GCNT and Pt/CNT catalysts were also performed and compared with Pt/C catalyst. According to current density @ 0.6 V after 10,000 potential cycles, Pt/GCNT, Pt/CNT and Pt/C catalysts can retain 61%, 67% and 60% of their performance, respectively.     

Self-assembled mesoporous carbon sensitized with ceria nanoparticles as durable catalyst support for PEM fuel cell

Mesocarbon-ceria nanocomposite is proposed for developing highly durable catalyst for the application in fuel cells. Ordered arrays of the mesoporous channels with d spacing of ∼8 nm and wall thickness of ∼3 nm are fabricated through a self-assembly route between the phenolic oligomers and PEO-containing P123 block polymer combined with self-assembly of CeOH₂⁺ and the surfactant. As a result, the Pt-mesocarbon-ceria presents a high electrochemically active surface of 105 m²/g_Pt. It is also found that ceria has an appreciable influence on the performance of the fuel cell at low humidity due to the water retention of ceria nanoparticles. At 75 RH% humidity of 65 °C, single cell assembled with Pt-mesocarbon-ceria has performance better than that of the conventional Pt/C catalyst. The Pt-mesocarbon-ceria displays high resistance to corrosion because of radical scavenges of ceria. Under long period operation at open circuit voltage (OCV), the voltage of the fuel cell assembled with Pt-mesocarbon-ceria has a slight decay rate of 9.5 μV/min, in comparison to 28.5 μV/min of conventional Pt/C. After an OCV accelerated degradation of 2000 min, the electrochemically active surface of Pt-mesocarbon-ceria is 45%, much lower than 70% of Pt/C catalyst.     

Durability of PEM fuel cell electrocatalysts prepared by microwave irradiation technique

In this study, the durability of the PEM fuel cell electrocatalysts was investigated by using cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques. Accelerated degradation tests (ADTs) were applied to the commercial catalysts and the electrocatalysts prepared by microwave irradiation technique in order to determine the platinum dissolution/agglomeration and carbon corrosion characteristics. The parameters examined for the commercial catalysts were carbon to Nafion (C/N) ratio in the catalyst ink and Pt loading over the carbon support. The parameters examined for the home-made catalysts were the conditions altered in the microwave environment including the base concentration and microwave duration. The hydrogen oxidation reaction (HOR) and oxygen reduction reactions (ORR) were examined before and after ADTs. The results showed that the catalyst properties differently affect the HOR and ORR activities of the catalysts before and after ADTs.     

Influence of carbon nanofiber properties as electrocatalyst support on the electrochemical performance for PEM fuel cells

Novel carbonaceous supports for electrocatalysts are being investigated to improve the performance of polymer electrolyte fuel cells. Within several supports, carbon nanofibers blend two properties that rarely coexist in a material: a high mesoporosity and a high electrical conductivity, due to their particular structure. Carbon nanofibers have been obtained by catalytic decomposition of methane, optimizing growth conditions to obtain carbon supports with different properties. Subsequently, the surface chemistry has been modified by an oxidation treatment, in order to create oxygen surface groups of different nature that have been observed to be necessary to obtain a higher performance of the electrocatalyst.     

Low-cost and durable catalyst support for fuel cells: Graphite submicronparticles

Low-cost graphite submicronparticles (GSP) are employed as a possible catalyst support for polymer electrolyte membrane (PEM) fuel cells. Platinum nanoparticles are deposited on Vulcan XC-72 carbon black (XC-72), carbon nanotubes (CNT), and GSP via ethylene glycol (EG) reduction method. The morphologies and the crystallinity of Pt/XC-72, Pt/CNT, and Pt/GSP are characterized with X-ray diffraction and transmission electron microscope, which shows that Pt nanoparticles (∼3.5 nm) are uniformly dispersed on supports. Pt/GSP exhibits the highest activity towards oxygen-reduction reactions. The durability study indicates that Pt/GSP is 2-3 times durable than Pt/CNT and Pt/XC-72. The enhanced durability of Pt/GSP catalyst is attributed to the higher corrosion resistance of graphite submicronparticles, which results from higher graphitization degree of GSP support. Considering its low production cost, graphite submicronparticles are promising electrocatalyst support for fuel cells.     

Synthesis and characterization of carbon nanotubes supported platinum nanocatalyst for proton exchange membrane fuel cells

Multi-walled carbon nanotubes (MWCNTs) were used as catalyst support for depositing platinum nanoparticles by a wet chemistry route. MWCNTs were initially surface modified by citric acid to introduce functional groups which act as anchors for metallic clusters. A two-phase (water-toluene) method was used to transfer PtCl₆²⁻ from aqueous to organic phase and the subsequent sodium formate solution reduction step yielded Pt nanoparticles on MWCNTs. High-resolution TEM images showed that the platinum particles in the size range of 1-3 nm are homogeneously distributed on the surface of MWCNTs. The Pt/MWCNTs nanocatalyst was evaluated in the proton exchange membrane (PEM) single cell using H₂/O₂ at 80 °C with Nafion-212 electrolyte. The single PEM fuel cell exhibited a peak power density of about 1100 mW cm⁻² with a total catalyst loading of 0.6 mg Pt cm⁻² (anode: 0.2 mg Pt cm⁻² and cathode: 0.4 mg Pt cm⁻²). The durability of Pt/MWCNTs nanocatalyst was evaluated for 100 h at 80 °C at ambient pressure and the performance (current density at 0.4 V) remained stable throughout. The electrochemically active surface area (64 m² g⁻¹) as estimated by cyclic voltammetry (CV) was also similar before and after the durability test.     

Synthesis and performance of platinum supported on ordered mesoporous carbons as catalyst for PEM fuel cells: Effect of the surface chemistry of the support

Platinum electrocatalysts supported on ordered mesoporous carbon (CMK-3) have been prepared as alternative catalysts for PEM fuel cells. Their performance has been compared with that of a commercial Pt-carbon black on carbon cloth electrode (E-TEK) for the hydrogen oxidation in a PEM single cell. Ordered mesoporous carbon was synthesized using nanocasting method and then platinum was deposited by incipient wetness impregnation. Before the platinum deposition, carbon support was functionalized using HNO₃ as oxidizing agent to modify its surface chemistry. The characterization study of the electrocatalysts demonstrated that the surface chemistry of the support has an important effect on both the physicochemical and electrochemical properties of electrocatalysts. For this catalyst synthesis method, functionalization did not improve the preparation of the catalyst, since the presence of surface oxygen groups facilitated the aggregation of metal particles. However, the Pt/CMK-3 based electrodes showed a better performance than the commercial one, which could be attributed to the porous structure of the support.     

Lignite as a fuel for direct carbon fuel cell system

Lignite, also known as brown coal, and char derived from lignite by pyrolysis were investigated as fuels for direct carbon solid oxide fuel cells (DC-SOFC). Experiments were carried out with 16 cm² active area, electrolyte supported solid oxide fuel cell (SOFC), using pulverized solid fuel directly fed to DC-SOFC anode compartment in a batch mode, fixed bed configuration. The maximum power density of 143 mW/cm² was observed with a char derived from lignite, much higher than 93 mW/cm² when operating on a lignite fuel. The cell was operating under electric load until fuel supply was almost completely exhausted. Reloading fixed lignite bed during a thermal cycle resulted in a similar initial cell performance, pointing to feasibility of fuel cell operation in a continuous fuel supply mode. The additional series of experiments were carried out in SOFC cell, in the absence of solid fuels, with (a) simulated CO/CO₂ gas mixtures in a wide range of compositions and (b) humidified hydrogen as a reference fuel composition for all cases considered. The solid oxide fuel cell, operated with 92%CO + 8%CO₂ gas mixture, generated the maximum power density of 342 mW/cm². The fuel cell performance has increased in the following order: lignite (DC-SOFC) < char derived from lignite (DC-SOFC) < CO + CO₂ gas mixture (SOFC) < humidified hydrogen (SOFC).