Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)‐Camphor‐10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI‐HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI‐HCl and/or carbon black were also carried out by using wave guide technique.     

Assessment of transport-limited catalyst utilization for engineering of ultra-low Pt loading polymer electrolyte fuel cell anode

In this study, transport-limited catalyst utilization in polymer electrolyte fuel cell (PEFC) anodes is assessed via an agglomerate model with a broader view of designing ultra-low Pt loading, high performance anode. The model accounts for electrical and chemical potential-driven transport of electrons/protons and dissolved hydrogen, respectively and multi-component gas-phase transport in the catalyst layer. The model employs the kinetics of hydrogen oxidation reaction based on dual-pathway reversible reaction mechanism reported recently [J.X. Wang, T.E. springer, R.R. Adzic, J. Electrochem. Soc. 153 (2006) A1732]. The model predictions show that for conventional, randomly-structured catalyst transport limitations exist at two levels. At single-agglomerate level, the catalyst utilization is restricted by dissolved hydrogen diffusivity limiting the reaction to occur primarily in the outer shell of the agglomerate. At the catalyst layer level, the catalyst utilization is limited primarily by poor protonic conductivity. However, significant electronic potential gradients can exist in the catalyst layer thereby effectively reducing the available overpotential. Simulation results also show that by engineering the catalyst layer to overcome the transport limitations and, thereby, improving the effective catalyst utilization, high performance can be achieved in a PEFC anode at ultra-low Pt loading of 0.0225 mg/cm².     

Synthesis and properties of a microporous carbon material as a catalyst support for fuel cells

It is stated that one-dimensional conductivity in amorphous microporous carbon material (AMCM) samples is associated with the considerable imperfection of graphene fragments in the carbon material rather than the presence of unshared electrons. It is likely that the graphene fragments are formed upon the carbonization of a carbon precursor accompanied by the partial or complete removal of precursor heteroatoms. It is hypothesized that the presence of localized unpaired electrons, which give EPR spectra, is due to the formation of local defects in carbene fragments. Thus, the effects of the value of conductivity and the concentration of unpaired electrons on the power output of a fuel cell cannot be distinguished based on the experimental data with the use of an AMCM as a catalyst support. The interaction of localized paramagnetic centers with electron gas can be interpreted in terms of the C-S relaxation model.     

Preparation of high catalyst utilization electrodes for polymer electrolyte fuel cells

We have developed a novel preparation procedure for an electrocatalyst layer with high utilization of catalyst for polymer electrolyte fuel cells. A commercial Pt catalyst supported on high surface area carbon black (Pt/CB) and Nafion ionomer solution was heated in an autoclave at 200 degrees C, followed by quenching to form the ink of the mixture. It was found that the cathode prepared with the new catalyst ink exhibited very high performance, i.e., high catalyst utilization and improved gas diffusivity. The microstructure analysis indicated that the autoclave treatment promoted an effective introduction of Nafion ionomer into primary pores of Pt/CB agglomerates, in which ca. 90% of Pt catalysts were supported. It was clearly observed by scanning transmission electron microscopy that Nafion ionomer was distributed more uniformly inside Pt/CB agglomerates, compared with those simply mixed with a ball mill in a conventional manner.     

Water management strategies for PGM-free catalyst layers for polymer electrolyte fuel cells

Platinum group metal–free (PGM-free) catalysts are promising candidates to catalyze the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs). Because of their low activity, larger loadings are used resulting in thicker catalyst layers. Transport, particularly water management, thereby becomes a more prominent performance factor. Currently, very few works attempted to understand water management in PGM-free catalyst layers, mainly because of other challenges that had to be overcome first, such as enhancing their activity and durability. The field has also been active in a hypothesis discussion of micropores flooding that led to the belief that poor stability of the PEFC performance is linked to active sites flooding within the micropores. We present here an overview of recent advances in understanding water management in the PGM-free catalyst layer for oxygen reduction reaction in PEFCs and provide an opinion on design guidance in optimizing catalyst layers to avoid flooding.     

Nb-TiO2 supported Pt cathode catalyst for polymer electrolyte membrane fuel cells

The Nb-doped TiO₂ nanostructure (Nb-TiO₂) was prepared as a support of metal catalyst in polymer electrolyte membrane fuel cells. Using the Nb-TiO₂ nanostructure support, we prepared the Nb-TiO₂ supported catalyst. The Nb-TiO₂ supported Pt catalyst (Pt/Nb-TiO₂) showed the well dispersion of Pt catalysts (∼3 nm) on the Nb-TiO₂ nanostructure supports (∼10 nm). The Pt/Nb-TiO₂ showed an excellent catalytic activity for oxygen reduction compared with carbon supported Pt cathode catalyst. The enhanced catalytic activity of Pt/Nb-TiO₂ in electrochemical half cell measurement may be mainly due to well dispersion of Pt nanoparticles on Nb-TiO₂ nanosized supports. In addition, from XANES spectra of Pt L edge obtained with the supported catalysts, the improved catalytic activity of Pt/Nb-TiO₂ for oxygen reduction may be caused by an interaction between oxide support and metal catalyst.     

Performance of catalyst layers of polymer electrolyte fuel cells: exact solutions

Performance of a catalyst layer of polymer electrolyte fuel cell under the assumptions of ideal transport of reactants and Tafel kinetics of electrochemical reaction is considered. Explicit expressions for the profiles of basic parameters (proton current density, overpotential and reaction rate) across the catalyst layer are obtained and a new conservation law is found. Exact expression for voltage–current curve of the catalyst layer is derived and simplified in the limiting cases of small and large current densities. The physics of transition from small to large currents is discussed.     

Composite anode catalyst layer for direct methanol fuel cell

A novel composite anode catalyst layer for direct methanol fuel cell is reported in this paper. The dual-layer anode, which is based on the catalyst coated membrane technique, characterizes a morphological variety of the catalyst layer. The inner sub-layer with a dense morphology can effectively suppress methanol crossover. On the other hand, the outer sub-layer modified by the pore-forming agent, NH₄HCO₃ and the carbon nanotubes can enhance the electrochemical surface area and increase the catalyst utilization. The structural improvement of anode catalyst layer results in a 40% increment in maximum power density during the single cell test at 30 °C.     

On-line mass spectrometry study of carbon corrosion in polymer electrolyte membrane fuel cells

The electrochemical corrosion of carbon catalyst supports in polymer electrolyte membrane (PEM) fuel cells is investigated by monitoring the generation of CO₂ using an on-line mass spectrometer at a constant potential of 1.4 V. Our results suggest that carbon supports with a high degree of graphitization are more corrosion-resistant, which results in a dramatic improvement of the catalyst durability. We also show that CO₂ measurements performed using on-line mass spectrometry represent a time-effective and reliable method for studying the electrochemical corrosion of carbon supports in PEM fuel cells.     

Non-noble metal catalyst on carbon ribbon for fuel cell cathode

A non-noble metal Fe/N/C catalyst is prepared by pyrolyzing the ball-milled mixture of graphitized carbon ribbon, iron precursor, and nitrogen precursor in ammonia. The Fe/N/C catalyst shows high ORR activity in alkaline solution, together with much improved stability compared with Pt/C catalyst. In the catalyst, FeN particles are covered by graphitic carbon layers. The activity is proposed to originate from the FeN and Fe/N/C sites. The stability is explained by the protecting effect of the carbon layers surrounding the FeN particles. The ORR mechanism on the Fe/N/C catalyst is proposed to be similar with Pt/C catalyst based on the Tafel plots. The Fe/N/C catalyst shows great potential in ORR in alkaline solution, while the performance in acid still needs improvement.     

Effect of water electrolysis catalysts on carbon corrosion in polymer electrolyte membrane fuel cells

A new approach to preventing electrochemical carbon corrosion in the cathode of polymer electrolyte membrane fuel cells (PEMFCs) was developed. The addition of 2 wt % IrO(2) (0.016 mg cm(-2)) to the catalyst layer of the cathode was demonstrated to reduce the electrochemical corrosion of carbon by 76% at 1.6 V(NHE) and 70 °C compared with a commercial Pt/C catalyst of the same Pt loading of 0.4 mg cm(-2) and under the same test conditions. The IrO(2) was shown to behave as a catalyst for water electrolysis, thereby removing water from the catalyst layer, which promoted electrochemical carbon corrosion.     

Anti-flooding cathode catalyst layer for high performance PEM fuel cell

Water management in cathode catalyst layer (CCL) plays an important role in the PEM fuel cell operation. A novel anti-flooding CCL is developed with the addition of oxygen permeable and hydrophobic dimethyl silicone oil (DSO) into the catalyst layer (CL) to improve the water balance and oxygen transport within the cathode. With the addition of 0.5 mg cm^?2 DSO in the CCL, the ability of water management has been enhanced greatly compared to that with a normal cathode. Electrochemical impedance spectroscopy has been employed to characterize the electrochemical behavior of the single fuel cell. The results show that the increased hydrophobicity of the CCL by DSO modification effectively expels water out of the voids of CCL. In addition, DSO in the CCL enhances oxygen accessibility to the CCL, thus improving the performance of the PEM fuel cell significantly.     

Boron-doped diamond powder as catalyst support for fuel cell applications

The modification of boron-doped diamond powder with metallic oxides using the sol–gel method to prepare high area and very stable electrodes for the methanol oxidation reaction is reported here. The catalyst clusters thus prepared are irregularly distributed on the BDD powder surface having sizes varying between 500 nm and 5 μm and formed by the agglomeration of many nanoparticles. Electrochemical studies in acid media demonstrate that the deposited particles have a good electrical contact with the diamond powder surface and high purity. Moreover, the use of the sol–gel method on a BDD powder substrate leads to the formation of metallic and metallic oxides deposits of the desired composition. The electrocatalyst composite prepared in this manner (Pt–RuO_x/BDD powder) shows an excellent activity for methanol oxidation presenting an onset potential 20 mV lower than that observed on a Pt–Ru/C commercial catalyst, probably due to the ruthenium oxide contribution to the overall catalytic activity.     

Effects of microporous layer preparation on the performance of a direct methanol fuel cell

The effects of two different microporous layer (MPL) preparation methods, including a heated-spraying method and a scraping method, on the performance of a direct methanol fuel cell (DMFC) were investigated. The experimental results indicated the cell with the new MPL had a higher mass transfer rate of oxygen and better performance than that of the conventional MPL. Scanning electron microscopy (SEM) images showed that there were more cracks and voids on the surface of the new MPL than that of the conventional MPL. The cathode and anode polarization curves exhibited that the cell with conventional MPL decreased the cell performance due to the difficulty for mass transport. Electrochemical impedance spectra (EIS) analysis further demonstrated that the improved performance of the cell with new MPL was attributed to the enhanced oxygen transport as the result of the reduced mass transfer resistance in the fuel cell system.     

Hydrogen adsorption in microporous organic framework polymer

A microporous organic framework polymer (OFP) based on a polyimide framework exhibits a high surface area (1159 m(2) g(-1)) and shows a reversible H(2) storage capacity of 3.94 wt% at 10 bar and 77 K, the highest yet reported for an organic polymer.     

Design and synthesis of nitrogen-containing calcined polymer/carbon nanotube hybrids that act as a platinum-free oxygen reduction fuel cell catalyst

The development of a platinum-free catalyst is one of the challenging issues for the global commercialization of fuel cell systems. Here we describe the design and synthesis of nitrogen-containing calcined polybenzimidazole/carbon nanotube hybrids that act as an oxygen reduction catalyst.     

CO removal by two-stage methanation for polymer electrolyte fuel cell

In order to remove CO to achieve lower CO content of below 10 ppm in the CO removal step of reformer for polymer electrolyte fuel cell （PEFC） co-generation systems, CO preferential methanation under various conditions were studied in this paper. Results showed that, with a single kind of catalyst, it was difficult to reach both CO removal depth and CO2 conversion ratio of below 5%. Thus, a two-stage methanation process applying two kinds of catalysts is proposed in this study, that is, one kind of catalyst with relatively low activity and high selectivity for the first stage at higher temperature, and another kind of catalyst with relatively high activity and high selectivity for the second stage at lower temperature. Experimental results showed that at the first stage CO content was decreased from 1% to below 0.1% at 250-300 ℃, and at the second stage to below 10 ppm at 150-185 ℃. CO2 conversion was kept less than 5%, At the same time, influence of inlet CO content and GHSV on CO removal depth was also discussed in this paper.     

Improved lifetime of PEM fuel cell catalysts through polymer stabilization

A novel approach to increase lifetime of Pt/C catalysts was demonstrated and shown that Nafion-stabilized Pt catalyst (denoted here as Nafion-Pt/C) synthesized by a colloid route gives rise to an enhanced durability as compared to a conventional Pt/C catalysts commonly used in PEM fuel cell. A high catalytic activity of the catalyst is also observed by both CV (cyclic voltammetry) and ORR (oxygen reduction reaction) measurements. This catalyst durability in comparison with conventional Pt/C is increased directly by electrochemically-accelerated durability test (ADT). The loss rate of electrochemical active area (ECA) for Nafion-Pt/C catalysts is only 0.004 m² g⁻¹ cycle⁻¹, compared to a value of 0.012 m² g⁻¹ cycle⁻¹ for Pt/C. This indicates the catalyst is three times higher durability than Pt/C.