Enhanced durability of PdPt/C electrocatalyst during the ethanol oxidation reaction in alkaline media

Journal of Solid State Electrochemistry - Developing new electrocatalysts with greater catalytic activity and enhanced stability than Pt to power generation is essential due to high demands and...     

Colloid-imprinted carbon with superb nanostructure as an efficient cathode electrocatalyst support in proton exchange membrane fuel cell

Novel colloid-imprinted carbon material CIC-22 with tailored mesopore size of ca. 22 nm was explored for the first time as a cathode electrocatalyst support in proton exchange membrane fuel cell. The CIC-22 possesses unique structural characteristics including nonmicropores, large specific surface area and pore volume, well-developed interconnected mesoporosity, and high electrical conductivity as well. The superb characteristics of the CIC-22 make it a highly efficient catalyst support for low-temperature fuel cell. The CIC-22-supported Pt has demonstrated a great improvement in electrocatalytic activity toward oxygen reduction reaction and an enhancement of ca. 70% in power density in comparison with commercial carbon black Vulcan XC 72-supported one.     

Recent developments in catalyst-related PEM fuel cell durability

Cost and durability remain the two major barriers to the widespread commercialization of polymer electrolyte membrane fuel cell (PEMFC)-based power systems, especially for the most impactful but challenging fuel cell electric vehicle (FCEV) application. Commercial FCEVs are now on the road; however, their PEMFC systems do not meet the cost targets established by the U.S. Department of Energy, primarily due to the high platinum loading needed on the cathode to achieve the requisite performance and lifetime. While the activities of a number of commercial Pt-based alloy cathode catalysts exceed the beginning-of-life (BOL) targets, these activities, and the overall cathode performance, degrade via a variety of mechanisms described herein. Degradation is mitigated in current FCEVs by utilizing a cathode catalyst with a lower BOL activity (e.g., much lower transition metal alloy content and larger BOL nanoparticle size), necessitating higher catalyst loadings, and through the utilization of system controls that avoid conditions known to exacerbate degradation processes, such as limiting the fuel cell stack voltage range. The design and development of active and robust materials and eliminating the need for vehicle mitigation strategies would greatly simplify the operating system, allowing for greater transient operation, avoiding large hybridization, and curtailing of fuel cell power. Although system mitigation strategies have provided the near-term pathway for FCEV commercialization, material-specific solutions are required to further reduce costs and improve operability and efficiency. Future material developments should focus on stabilization of the electrode structure and minimization of the catalyst particle susceptibility to dissolution caused by oxide formation and reduction over PEMFC cathode-relevant operating potentials plus minimization of support corrosion. Ex situ accelerated stress tests have provided insight into the processes responsible for material and performance degradation and will continue to provide useful information on the relative stability of materials and benchmarks for robust and stable materials-based solutions not requiring system mitigation strategies to achieve adequate lifetime.     

Synthesis and characterization of Pd-La(OH)3/C electrocatalyst for direct ethanol fuel cell

The composite nanomaterial of Pd-La(OH)₃/C was successfully synthesized via intermittent microwave heating–glycol reduction method and characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The TEM photograph shows that Pd-La(OH)₃ is well polymerized and dispersed on the carbon support. The performance of the prepared material for ethanol oxidation was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and chronopotentiometry (CP) measurements in alkaline media. The results reveal that Pd-La(OH)₃/C has significantly higher activity and stability than that of Pd/C with the same Pd loading of 0.1 mg cm^?2. The stable potential reaches to ?0.38 V vs. Hg/HgO at 20 mA cm^?2 on the Pd-La(OH)₃/C electrode in CP curve. Single direct ethanol fuel cell (DEFC) was constructed using Pd-La(OH)₃/C electrode and MnO₂/C electrode as the ethanol anode and air cathode respectively, where the cell voltage can stay at 0.4 V under the current density of 20 mA cm^?2 by discharge test at room temperature.     

Supportless PdFe nanorods as highly active electrocatalyst for proton exchange membrane fuel cell

The PdFe nanorods (PdFe-NRs) with tunable length were synthesized by an organic phase reaction of [Pd(acac)₂] and thermal decomposition of [Fe(CO)₅] in a mixture of oleyamine and octadecene at 160 °C. They show a better proton exchange membrane fuel cell (PEMFC) performance than commercial Pt/C in working voltage region of 0.80–0.65 V, due to their high intrinsic activity to oxygen reduction reaction (ORR), reduced cell inner resistance, and improved mass transport.     

Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.     

Fluorene-containing block sulfonated poly(ether ether ketone) as proton-exchange membrane for PEM fuel cell application

A series of sulfonated block poly(ether ether ketone)s with different sulfonic acid group clusters were successfully synthesized by nucleophilic displacement condensation. Membranes were accordingly cast from their DMSO solutions, and fully characterized by determining the ion-exchange capacity, water uptake, proton conductivity, dimensional stabilities and mechanical properties. The experimental results showed that the main properties of the membrane can be tailored by changing the cluster size of sulfonic acid groups. The membrane of block-7c(40) has good mechanical, oxidative and dimensional stabilities together with high proton conductivity (5.09 × 10⁻² S cm⁻¹) at 80 °C under 100% relative humidity. The membranes also possess excellent thermal and dimensional stabilities. These polymers are potential and promising proton conducting membrane material for PEM full cell applications.     

Electrochemical H/D isotope effects in PEM fuel cell

An electrochemical H/D separation system consisting of electrolyzer and PEM fuel cell has been proposed. Isotope separation could be important as a part of the energy saving process in an energy-hydrogen-energy cycle. Any transfer of energy into hydrogen or vice versa induces change of the H/D isotope ratio, which can be considered, as a method to produce heavy water as by-product. In this way, the separation efficiency can contribute to the overall efficiency of the cycle.     

Polypyrrole/Co-tetraphenylporphyrin modified carbon fibre paper as a fuel cell electrocatalyst of oxygen reduction

A thin-layer of polypyrrole (PPy) film, immobilized with neutral 5,10,15,20-tetraphenylporphyrinato cobalt (II) (Co-TPP), was successfully and uniformly deposited onto mesoporous carbon fibre paper (CFP) via vapor-phase polymerization. The resulting PPy/Co-TPP-modified carbon fibre paper (PPy/Co-TPP-CFP) electrode was characterized by cyclic voltammetry, SEM and EDX-ray mapping. Its electrochemical stability and long-term electrocatalytic performance were investigated in a half-fuel cell testing system. The electrode displayed significant electrocatalytic performance for oxygen reduction at 0.0 V (vs. Ag/AgCl), with notable long-term stability.     

Corrosion analysis of graphite sinter as bipolar plates in the low-temperature PEM fuel cell simulated environments

Journal of Solid State Electrochemistry - The article presents the results of research and an analysis of the possibility of using sinters made of graphite powder as a material dedicated to the...     

PtCeOx/C as a novel methanol-tolerant electrocatalyst of oxygen reduction for direct methanol fuel cells

A prominent methanol-tolerant characteristic of the PtCeO_x/C electrocatalyst was found during oxygen reduction reaction process. The carbon-supported platinum modified with cerium oxide (PtCeO_x/C) as cathode electrocatalyst for direct methanol fuel cells was prepared via a simple and effective route. The synthesized electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. It was found that the cerium oxide within PtCeO_x/C present in an amorphous form on the carbon support surface and the PtCeO_x/C possesses almost similar disordered morphological structure and slightly smaller particle size compared with the unmodified Pt/C catalyst.     

Molecular oxygen reduction in PEM fuel cell conditions: ToF-SIMS analysis of co-based electrocatalysts

A series of Co-based electrocatalysts for oxygen reduction in acid media has been prepared using two different Co precursors: cobalt acetate (CoAc) and a cobalt porphyrin (CoTMPP). These catalysts have been analyzed by ToF-SIMS to obtain information on the number and the structure of catalytic active sites in these materials. The results are compared with the results of a similar analysis already performed on a series of Fe-based electrocatalysts (J. Phys. Chem. B 2002, 106, 8705) also prepared with two different Fe precursors: iron acetate (FeAc) and an iron porphyrin (ClFeTMPP). The interpretation of ToF-SIMS data for Fe-based catalysts allowed us to conclude that whatever the Fe precursor was, the same catalytic sites (FeN2/C and FeN4/C, with their respective dominant ToF-SIMS signatures: FeN2C4+ and FeN4C8+ ions) were found. The comparison of the ToF-SIMS data with the activity of those catalysts led to the conclusion that the FeN2C catalytic site was more active than FeN4/C. When the same procedure is applied to ToF-SIMS data measured for Co-based catalysts, the following conclusions are drawn: (i) as for Fe precursors, both Co precursors also give similar results; (ii) as for Fe-based catalysts, the same four families of MetalNxCy+ ions, with 1, 2, 3, and 4 nitrogen atoms, are also found in the spectra of Co-based catalysts, but there is no dominant CoNxCy+ ion signature; (iii) only CoN4/C can be ascertained on the basis of ToF-SIMS measurements. There is no strong support from ToF-SIMS measurements for (or against) the existence of CoN2/C in Co-based catalysts as there is for FeN2/C in Fe-based catalysts; (iv) contrary to Fe-based catalysts, all catalytic sites (if there are any besides CoN4/C) are about equally active in Co-based electrocatalysts.     

Polypyrimidine/SWCNTS composite comprising Pt nanoparticles: Possible electrocatalyst for fuel cell

The poly(9,9-dioctyl fluorine-alt-2-amino-4,6-pyrimidine) (oligomer) is used as an effective dispersant for single walled carbon nanotubes (SWCNTs) and generates stable SWCNTs hybrid after elimination of the excess polymer. The covered polymers immobilized Pt nanoparticles onto the surface of single-walled carbon nanotubes (SWCNTs) by coordination between Pt and polymer and the amount of the loaded Pt on the hybrid was calculated to be 38.5 wt %. The average diameter of the Pt nanoparticles on the SWCNTs were about ～4–5 nm and have a moderate electrochemically active surface area of 40.5 m²/g. These studies strongly imply the possible application of novel pyrimidine/carbon materials as catalyst supports in the electrodes of fuel cells.     

Pt/porous-IrO2 nanocomposite as promising electrocatalyst for unitized regenerative fuel cell

Pt/porous-IrO₂ composite as bifunctional oxygen electrocatalyst for unitized regenerative fuel cell has been prepared by chemical reduction of Pt on porous IrO₂ which is obtained via template-removal method. X-ray diffraction and transmission electron microscopy characterizations indicate that the Pt nanoparticles (ca. 4.4 nm) are deposited on both internal and external sites of porous IrO₂ nanoparticles. Electrochemical analyses show that the activity toward oxygen evolution reaction on Pt/porous-IrO₂ catalyst is 28% (at 1.55 V) higher than that on Pt/commercial-IrO₂ catalyst, and the activity towards oxygen reduction reaction on the former is 2.3 times (at 0.85 V) that on the latter. Oxygen reduction on Pt/porous-IrO₂ catalyst follows the first-order kinetics and the four-electron mechanism.     

Computational analysis of heat transfer in a PEM fuel cell with metal foam as a flow field

Journal of Thermal Analysis and Calorimetry - Thermal management of proton-exchange membrane (PEM) fuel cell has an important effect on the overall cell performance. In this paper, metal foams as...     

Chemical and mechanical stability of EPDM in a PEM fuel cell environment

Proton exchange membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. Long-term durability of the fuel cell stacks depends heavily on the functionality of the elastomeric gasket material. Chemical and mechanical stability of the elastomeric material is of great concern to the overall performance of the fuel cell stacks. The degradation of a commercially available gasket material, ethylene-propylene-diene monomer (EPDM), was investigated in a simulated PEM fuel cell environment in this work. One solution and two temperatures, based on actual fuel cell operation, were used in this study. Optical microscopy was used to show the topographical changes on the sample surface. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the gasket material before and after exposure to the simulated PEM fuel cell environment over time. Atomic absorption spectrometry was used to identify the leachants in the soaking solution from the elastomeric material. Microindentation test and dynamic mechanical analysis (DMA) were conducted to assess the change of mechanical properties of the samples exposed to the environment. The atomic absorption spectrometer analysis shows that silicon and calcium were leached from the material into the soaking solution. The ATR-FTIR results indicate that the chemical changes were not apparent. The microindentation test and DMA results reveal that mechanical properties were not changed significantly.     

Zero-CO2 emission and low-crossover 'rechargeable' PEM fuel cells using cyclohexane as an organic hydrogen reservoir

High performance (open circuit voltage = 920 mV, maximum power density = 14-15 mW cm(-2)) of the PEM fuel cell was achieved by using cyclohexane as a fuel with zero-CO2 emission and lower-crossover through PEM than with a methanol-based fuel cell.     

Modification of multi-walled carbon nanotubes by microwave digestion method as electrocatalyst supports for direct methanol fuel cell applications

Multi-walled carbon nanotubes (MWCNTs) which were directly synthesized on carbon cloth were modified by a microwave digestion method in 5 M HNO₃ for supporting Pt nanoparticles. The characterizations of modified CNTs were carried out by TEM, XPS, FTIR and Raman spectroscopy. The HRTEM image shows the caps of MWCNTs are opened after modifying by microwave digestion method. The open-end and undamaged MWCNTs can provide a larger surface area for supporting more catalysts. Furthermore, the methanol electrocatalytic oxidation of microwave digestion treated Pt/MWCNTs electrode shows higher current density than pristine and nitric acid-treated MWCNTs from cyclic voltammograms. This can be an effective and undamaged method for modifying CNTs.     

Platinum dissolution and deposition in the polymer electrolyte membrane of a PEM fuel cell as studied by potential cycling

The behavior of platinum dissolution and deposition in the polymer electrolyte membrane of a membrane-electrode-assembly (MEA) for a proton-exchange membrane fuel cell (PEMFC) was studied using potential cycling experiment and high-resolution transmission electron microscopy (HRTEM). The electrochemically active surface area decreased depending on the cycle number and the upper potential limit. Platinum deposition was observed in the polymer electrolyte membrane near a cathode catalyst layer. Platinum deposition was accelerated by the presence of hydrogen transported through the membrane from an anode compartment. Platinum was transported across the membrane and deposited on the anode layer in the absence of hydrogen in the anode compartment. This deposition was also affected by the presence of oxygen in the cathode compartment.