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.     

Hierarchy carbon paper for the gas diffusion layer of proton exchange membrane fuel cells

This communication described the fabrication of a hierarchy carbon paper, and its application to the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells. The carbon paper was fabricated by growing carbon nanotubes (CNTs) on carbon fibers via covalently assembling metal nanocatalysts. Surface morphology observation revealed a highly uniform distribution of hydrophobic materials within the carbon paper. The contact angle to water of this carbon paper was not only very large but also particularly even. Polarization measurements verified that the hierarchy carbon paper facilitated the self-humidifying of PEM fuel cells, which could be mainly attributed to its higher hydrophobic property as diagnosed by electrochemical impedance spectroscopy (EIS).     

Platinum decorated aligned carbon nanotubes: Electrocatalyst for improved performance of proton exchange membrane fuel cells

This study aims to improve the performance of proton exchange membrane fuel cells (PEMFCs) using carbon nanotubes as scaffolds to support nanocatalyst for power generation over prolonged time periods, compared to the current designs. The carbon nanotubes are prepared using chemical vapor deposition and decorated by platinum nanoparticles (Pt-NPs) using an amphiphilic approach. The PEMFC devices are then constructed using these aligned carbon nanotubes (ACNTs) decorated with Pt-NPs as the cathode. The electrochemical analyses of the PEMFC devices indicate the maximum power density reaches to 860 mW cm⁻² and current density reaches 3200 mA cm⁻² at 0.2 V, respectively, when O₂ is introduced into cathode. Importantly, the Pt usage was decreased to less than 0.2 mg cm⁻², determined by X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy as complimentary tools. Electron microscopic analyses are employed to understand the morphology of Pt-ACNT catalyst (with diameter of 4-15 nm and length from 8 to 20 μm), which affects PEMFC performance and durability. The Pt-ACNT arrays exhibit unique alignment, which allows for rapid gas diffusion and chemisorption on the catalyst surfaces.     

Functionalizing carbon nanotubes for proton exchange membrane fuel cells electrode

In recent years, carbon nanotubes (CNTs) have been increasingly considered as an advanced metal catalyst support for proton exchange membrane fuel cells (PEMFCs), owing to their outstanding physical and mechanical characteristics. However, the effective attachment of metal catalysts, uniformly dispersed onto the CNT surface, remains a formidable challenge because of the inertness of the CNT walls. Therefore, the surface functionalization of CNTs seems necessary in most cases in order to enable a homogeneous metal deposition. This review presents the different surface functionalization approaches that provide efficient avenues for the deposition of metal nanoparticles on CNTs, for the application of catalyst supports in PEMFCs with improved reactivity.     

Improving proton exchange membrane fuel cell performance with carbon nanotubes as the material of cathode microporous layer

The cathode microporous layer (MPL) is fabricated by various multiwall carbon nanotubes (CNTs), and its influence on the performance of a proton exchange membrane fuel cell (PEMFC) is evaluated. Three types of CNT with different dimensions are employed in the experiments, and the conventional MPL made by acetylene black (AB) is also considered for the purpose of comparison. The results show that the employment of CNT as MPL composition indeed may improve fuel cell performance significantly in comparison with the case of AB. The type of CNT with the largest tube diameter and straight cylinder in shape exhibits the highest cell performance. The corresponding optimal CNT loading and polytetrafluoroethylene (PTFE) content in the MPL are also evaluated. Results show that the case of cathode MPL composed of 1.5 mg cm^?2 CNT and 20 wt% PTFE exhibits the best performance in all the experimental cases. The present data reveal that the application of CNT for MPL fabrication is beneficial to promote PEMFC performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Development and characterization of tubular direct methanol fuel cells for use in in situ NMR analysis

The present study developed a tubular direct methanol fuel cell (tubular DMFC) for use in in situ Nuclear Magnetic Resonance (NMR) that could monitor various electrochemical reactions in real time. The tubular DMFC was fabricated in such a way as to prevent corrosion of cell components and to facilitate a supply of the reactants and removal of the products. The cell showed improved performance and durability sufficient for its use in an in situ NMR test, but problems with rapid performance decay persisted. Detailed reasons for the performance degradation were investigated through rigorous analytical work using various techniques. The tubular DMFC was also installed in an NMR probe to test signal sensitivity and resolution of ²D NMR spectra for deuterated methanol (CD₃OH) and deuterated water (D₂O). The spectral resolutions of both species were high, and their signal intensities were strong enough to realize an acceptable spectra.     

High loading and monodispersed Pt nanoparticles on multiwalled carbon nanotubes for high performance proton exchange membrane fuel cells

Composite electrodes consisting of Pt nanoparticles-supported on multiwalled carbon nanotubes grown directly on carbon paper (Pt/CNTs/carbon paper) have been synthesized by a new method using glacial acetic acid as a reducing agent. Transmission electron microscopy (TEM) images show that the Pt nanoparticles with high density and relative small in size (2–4 nm) were monodispersed on the surface of CNTs. X-ray photoelectron spectroscopy (XPS) analysis indicates that the glacial acetic acid acts as a reducing agent and has the capability of producing a high density of oxygen-containing functional groups on the surface of CNTs that leads to high density and monodispersion of Pt nanoparticles. Compared with standard Pt/C electrode, the Pt/CNT/carbon paper composite electrodes exhibit higher electrocatalytic activity for methanol oxidation reaction and higher single-cell performance in a H₂/O₂ fuel cell.     

Inkjet printing of carbon supported platinum 3-D catalyst layers for use in fuel cells

We present a method of using inkjet printing (IJP) to deposit catalyst materials onto gas diffusion layers (GDLs) that are made into membrane electrode assemblies (MEAs) for polymer electrolyte fuel cell (PEMFC). Existing ink deposition methods such as spray painting or screen printing are not well suited for ultra low (<0.5 mg Pt cm⁻²) loadings. The IJP method can be used to deposit smaller volumes of water based catalyst ink solutions with picoliter precision provided the solution properties are compatible with the cartridge design. By optimizing the dispersion of the ink solution we have shown that this technique can be successfully used with catalysts supported on different carbon black (i.e. XC-72R, Monarch 700, Black Pearls 2000, etc.). Our ink jet printed MEAs with catalyst loadings of 0.020 mg Pt cm⁻² have shown Pt utilizations in excess of 16,000 mW mg⁻¹ Pt which is higher than our traditional screen printed MEAs (800 mW mg⁻¹ Pt). As a further demonstration of IJP versatility, we present results of a graded distribution of Pt/C catalyst structure using standard Johnson Matthey (JM) catalyst. Compared to a continuous catalyst layer of JM Pt/C (20% Pt), the graded catalyst structure showed enhanced performance.     

Preparation and evaluation of electrodeposited platinum nanoparticles on in situ carbon nanotubes grown carbon paper for proton exchange membrane fuel cells

Multi-walled carbon nanotubes (MWCNTs) based microporous layer on the non-woven carbon paper substrates was prepared by in situ growth in a chemical vapor deposition method. Pt with a loading of ～0.13 mg cm^?2 was electrodeposited at ?0.3, ?0.6, ?1.2, ?2.4, and ?3.6 V vs SCE in a chloroplatinic acid (60 g/L) and hydrochloric acid (10 g/L) bath using a potentiostat. Scanning electron micrographs showed that the Pt nanoparticles decorated on the MWCNTs/carbon paper are highly uniform, especially at an electrodeposition voltage of ?0.6 V vs SCE. Pt particles' size at various deposition potentials, as estimated by X-ray diffraction analysis is in nanosize range with an average diameter of 6 nm. Fuel cell performance of the Pt deposited in situ grown MWCNTs carbon paper was evaluated using Nafion-212 membrane at various operating conditions. The cathode with Pt deposition at ?0.6 V showed a power density of ～640 mW cm^?2 at 80 °C using H₂ and O₂ at 90% RH and 101 kPa.     

Highly uniform platinum nanoparticles supported on graphite nanoplatelets as a catalyst for proton exchange membrane fuel cells

Graphite nanoplatelets (GNPs), which consist of layers of graphene, are an ideal electrocatalyst support due to their high electrical and thermal conductivity, excellent chemical stability, and easy availability. However, GNPs are somewhat chemically inert, which makes the even deposition of catalytic metal nanoparticles on their surface difficult. In this paper, we present a facile method to prepare highly uniform Pt nanoparticles on GNPs, which are decorated with 1-pyrenecarboxylic acid (PCA). When the hydrophobic pyrene group of the PCA is adsorbed on the surface of GNPs via π–π interaction, its carboxylic group can serve as an anchor for the Pt deposition. This decoration facilitates a narrow size profile, which is centered at approximately 2–3 nm, and an even spatial distribution on the GNPs surface for the Pt nanoparticles. The resultant Pt/GNPs catalyst exhibits a noticeably higher durability and electrochemical activity than the commonly used Pt/C catalyst and is therefore a promising cathodic catalyst for proton exchange membrane fuel cells.     

Pd nanoparticles deposited on vertically aligned carbon nanotubes grown on carbon paper for formic acid oxidation

Vertically aligned carbon nanotubes (VACNTs) grown on carbon paper were obtained by the spray pyrolysis method and highly dispersed Pd nanoparticles were deposited on VACNTs by the wet chemical method. For comparison, the entangled carbon nanotubes (ECNTs) and Vulcan XC-72 based electrodes were fabricated by brush painting the corresponding Pd/ECNTs and Pd/XC-72 catalysts on carbon paper, respectively. Compared with Pd deposition on the entangled carbon nanotubes (ECNTs) and Vulcan XC-72 electrodes, the VACNTs electrode exhibited higher activity for formic acid oxidation, which is mainly due to the three-dimensional structure and better conductive paths in the VACNTs electrode, as well as higher Pd utilization.     

In situ metal ion contamination and the effects on proton exchange membrane fuel cell performance

Automotive fuel cell technology has made considerable progress, and hydrogen fuel cell vehicles are regarded as a possible long-term solution to reduce carbon dioxide emissions, reduce fossil fuel dependency and increase energy efficiency. Even though great strides have been made, durability is still an issue. One key challenge is controlling MEA contamination. Metal ion contamination within the membrane and the effects on fuel cell performance were investigated. Given the possible benefits of using stainless steel or aluminum for balance-of-plant components or bipolar plates, cations of Al, Fe, Ni and Cr were studied. Membranes were immersed in metal sulfide solutions of varying concentration and then assembled into fuel cell MEAs tested in situ. The ranking of the four transition metals tested in terms of the greatest reduction in fuel cell performance was: Al³⁺ ? Fe²⁺ > Ni²⁺, Cr³⁺. For iron-contaminated membranes, no change in cell performance was detected until the membrane conductivity loss was greater than approximately 15%.     

Tungsten oxide nanowires grown on carbon paper as Pt electrocatalyst support for high performance proton exchange membrane fuel cells

Tungsten oxide nanowires (W₁₈O₄₉ NWs) were directly grown on carbon paper by chemical vapor deposition. Well-dispersed Pt nanoparticles, with a size distribution from 2 to 4 nm, were deposited on the surface of W₁₈O₄₉ NWs through a simple reductive process. The resulting Pt/W₁₈O₄₉ NW/carbon paper composites formed a three-dimensional electrode structure. In comparison to conventional Pt/C electrocatalyst, the Pt/W₁₈O₄₉ NW/carbon paper composite exhibited higher electrocatalytic activity toward the oxygen reduction reaction and better CO tolerance in a single cell polymer electrolyte membrane fuel cell.     

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.     

Study on the membrane electrode assembly fabrication with carbon supported cobalt triethylenetetramine as cathode catalyst for proton exchange membrane fuel cell

An improved fabrication technique for conventional hot-pressed membrane electrode assemblies (MEAs) with carbon supported cobalt triethylenetetramine (CoTETA/C) as the cathode catalyst is investigated. The V-I results of PEM single cell tests show that addition of glycol to the cathode catalyst ink leads to significantly higher electrochemical performance and power density than the single cell prepared by the traditional method. SEM analysis shows that the MEAs prepared by the conventional hot-pressed method have cracks between the cathode catalyst layer and Nafion membrane, and the contact problem between cathode catalyst layer and Nafion membrane is greatly suppressed by addition of glycol to the cathode catalyst ink. Current density-voltage curve and impedance studies illuminate that the MEAs prepared by adding glycol to the cathode catalyst ink have a higher electrochemical surface area, lower cell ohmic resistance, and lower charge transfer resistance. The effects of CoTETA/C loading, Nafion content, and Pt loading are also studied. By optimizing the preparation parameters of the MEA, the as-fabricated cell with a Pt loading of 0.15 mg cm⁻² delivers a maximum power density of 181.1 mW cm⁻², and a power density of 126.2 mW cm⁻² at a voltage of 0.4 V.     

Effects of surface chemical states of carbon nanotubes supported Pt nanoparticles on performance of proton exchange membrane fuel cells

This study synthesized platinum (Pt) nanoparticles supported on carbon nanotubes (CNTs) using a microwave-assisted polyol method. The oxidation treatment of CNTs introduced primarily -OH and -COOH groups to the CNTs, thereby enhancing the reduction of Pt ionic species, resulting in smaller Pt particles with improved dispersion and attachment properties. The Pt particles supported on oxidized CNTs displayed superior durability to those on pristine CNTs or commercially available Pt/C. These improvements are most likely associated with the percentage of metallic Pt in the particles. After 400 cycles, the losses of electrochemical surface area in Pt nanoparticle supported on oxidized CNTs and pristine CNTs catalysts were 66 and 84%, respectively, of that associated with commercial Pt/C. A single proton exchange membrane fuel cell using Pt supported on oxidized CNTs at the cathode with a total catalytic loading of 0.6 Pt mg cm⁻² exhibited the highest power density of 890 mW cm⁻² and displayed a lower mass transfer loss, compared to Pt/C.     

Effects of sulfonated polyether-etherketone (SPEEK) and composite membranes on the proton exchange membrane fuel cell (PEMFC) performance

Sulfonated polyether-etherketone (SPEEK) has a potential for proton exchange fuel cell applications. However, its conductivity and thermohydrolytic stability should be improved. In this study the proton conductivity was improved by addition of an aluminosilicate, zeolite beta. Moreover, thermohydrolytic stability was improved by blending poly-ether-sulfone (PES). Sulfonated polymers were characterized by H-NMR. Composite membranes prepared were characterized by Electrochemical Impedance Spectroscopy (EIS) for their proton conductivity. Degree of sulfonation (DS) values calculated from H-NMR results, and both proton conductivity and thermohydrolytic stability was found to strongly depend on DS. Therefore, DS values were controlled time in the range of 55–75% by controlling the reaction time. Zeolite beta fillers at different SiO₂/Al₂O₃ ratios (20, 30, 40, 50) were synthesized and characterized by XRD, EDX, TGA, and SEM. The proton conductivity of plain SPEEK membrane (DS = 68%) was 0.06 S/cm at 60 °C and the conductivity of the composite membrane containing of zeolite beta filled SPEEK was found to increase to 0.13 S/cm. Among the zeolite Beta/SPEEK composite membranes the best conductivity results were achieved with zeolite beta having a SiO₂/Al₂O₃ ratio of 50 at 10 wt% loading.     

Effect of platinum amount in carbon supported platinum catalyst on performance of polymer electrolyte membrane fuel cell

The performance of polymer electrolyte membrane fuel cells fabricated with different catalyst loadings (20, 40 and 60 wt.% on a carbon support) was examined. The membrane electrode assembly (MEA) of the catalyst coated membrane (CCM) type was fabricated without a hot-pressing process using a spray coating method with a Pt loading of 0.2 mg cm⁻². The surface was examined using scanning electron microscopy. The catalysts with different loadings were characterized by X-ray diffraction and cyclic voltammetry. The single cell performance with the fabricated MEAs was evaluated and electrochemical impedance spectroscopy was used to characterize the fuel cell. The best performance of 742 mA cm⁻² at a cell voltage of 0.6 V was obtained using 40 wt.% Pt/C in both the anode and cathode.