Oxygen reduction reaction increased tolerance and fuel cell performance of Pt and RuxSey onto oxide-carbon composites

Pt and Ru_xSe_y nanoparticles were selectively deposited onto oxide sites of oxide-carbon composite substrates using the photo-deposition process and compared to conventional carbon support materials. The oxide was essentially anatase phase. Cyclic voltammetry and rotating disk electrode measurements for the oxygen reduction reaction (ORR) in formic acid containing-electrolyte showed a tolerance improvement for ORR of Pt supported on composite substrates. This positive substrate effect on platinum, turned out not to be favorable for Ru_xSe_y catalyst centers. On the other hand, the methanol tolerance for ORR was increased for both nanostructured materials supported on the oxide-carbon composite. Single H₂/O₂ fuel cell results were in agreement with half-cell electrochemical measurements on Pt, showing an improvement of the power density when using the oxide-carbon as substrate for the cathode. The composites were evaluated as cathode catalysts of an HCOOH laminar-flow fuel cell (LFFC) in which commercial Pd/C was used as an anode catalyst. The cathodes with Ru_xSe_y and Pt supported on TiO₂/C improved the specific power density by 15% and 24%, respectively, with respect to carbon as support.     

Direct methanol fuel cells: The effect of electrode fabrication procedure on MEAs structural properties and cell performance

In the present paper, the effect of electrode preparation procedure on the structural properties of membrane electrode assembly (MEA) and consequently on the performance of direct methanol fuel cells (DMFCs) was investigated. Commercial PtRu black anode catalyst and Pt black cathode catalyst were characterized by XRD in their initial form and in their intermediate and final states after each step involved in catalyst-coated membrane electrode preparation procedure by a decal transfer method (DTM). XRD results demonstrated that the DTM process has a significant effect on the catalyst structural properties, especially on the particle size of Pt black cathode catalyst. It is also discussed that among all the steps involved in the electrode fabrication procedure, catalyst ink preparation and high temperature transfer process are key factors affecting the particle size of Pt black catalyst. Furthermore, it was found that the maximum power density of the single DMFC using a MEA fabricated by the DTM, when air is used as oxidant, is more than two times greater than that of the cell using conventionally prepared MEA, and more than three times greater when pure oxygen is used as oxidant. This could be attributed to the easier mass transportation due to the thinner catalyst layer and the better contact between the catalyst layer and the electrolyte membrane in the former case, even if, according to in situ CO stripping voltammetry results in the fuel cell anode environment, the surface composition of PtRu anode has been changed.     

Pt-Pd nanodendrites as oxygen reduction catalyst in polymer-electrolyte-membrane fuel cell

Platinum-palladium (Pt-Pd) bimetallic alloys have shown prospect as electrocatalyst for the oxygen reduction reaction (ORR) in the cathode of polymer-electrolyte-membrane (PEM) fuel cells. This article reports a facile solvothermal synthesis of Pt-Pd bimetallic nanodendrites (Pt-Pd NDs). The characterization with a variety of spectroscopic techniques indicates that the Pt-Pd NDs possess a three-dimensional (3-D) porous structure consisting of interconnected branches of highly alloyed Pt-Pd nanorods (NR). The measurements using rotating disk electrode in electrolyte solution show that the catalyst of Pt-Pd NDs supported on carbon (Pt-Pd NDs/C) possesses a Pt mass activity for ORR that is more than 3 times higher than that of the state-of-the-art Pt/C catalyst, as well as the significantly improved stability due to the branched porous structure. The measurements using membrane-electrode-assembly (MEA) in a single PEM fuel cell indicate the 3-D interconnected dendrite structures make the Pt-Pd NDs/C catalyst significantly advantageous over the nanoparticle Pt/C catalyst in reducing the mass transport and ohmic polarization which would become significant at high current density in MEA.     

Cell performance of Pd–Sn catalyst in passive direct methanol alkaline fuel cell using anion exchange membrane

Direct methanol alkaline fuel cell (DMAFC) using anion exchange membrane (AEM) was operated in passive condition. Cell with AEM exhibits a higher open circuit voltage (OCV) and superior cell performance than those in cell using Nafion. From the concentration dependences of methanol, KOH in fuel and ionomer in anode catalyst layer, it is found that the key factors are to improve the ionic conductivity at the anode and to form a favorable ion conductive path in catalyst layer in order to enhance the cell performance. In addition, by using home-made Pd–Sn/C catalyst as a cathode catalyst on DMAFC, the membrane electrode assembly (MEA) using Pd–Sn/C catalyst as cathode exhibits the higher performance than the usual commercially available Pt/C catalyst in high methanol concentration. Therefore, the Pd–Sn/C catalyst with high tolerance for methanol is expected as the promising oxygen reduction reaction (ORR) catalyst in DMAFC.     

Performance increase of microfluidic formic acid fuel cell using Pd/MWCNTs as catalyst

This paper shows that the combination of an O₂ saturated acidic fluid setup (O₂-setup) and a composite of Pd nanoparticles supported on multiwalled-carbon nanotubes (Pd/MWCNTs) as anode catalyst material, results in the improvement of microfluidic fuel cell performance. Microfluidic fuel cells were constructed and evaluated at low HCOOH concentrations (0.1 and 0.5 M) using Pd/V XC-72 and Pd/MWCNTs as anode and Pt/V XC-72 as cathode electrode materials, respectively. The results show a higher power density (2.9 mW cm⁻²) for this cell when compared to the value reported in the literature that considers a commercial Pd/V XC-72 and 3.3 mW cm⁻² using a Pd/MWCNTs with a 50% less Pd loading than that commercial Pd/V XC-72.     

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).     

Evaluation of porous platinum,nickel, and lanthanum strontium cobaltite as electrode materials for low-temperature solid oxide fuel cells

Porous Pt, Ni, and lanthanum strontium cobaltite (LSC) are evaluated as electrode materials for solid oxide fuel cells at the low temperature range under 500 °C. Porous metal electrodes 150 nm thick are prepared by sputtering. Porous LSC was deposited to a typical thickness of 1.5 μm by pulsed laser deposition as the cathode. In terms of fuel cell performance, we confirm that Pt is the best material for both the cathode and the anode under 400 °C, but LSC outperforms Pt as a cathode at temperatures over 450 °C in our configurations. Porous Ni anode is identified as being less effective than the porous Pt. It is determined that these results are closely related to the differences in electrode performance and to morphological changes during fuel cell operation.     

On the mesoporous TiN catalyst support for proton exchange membrane fuel cell

A mesoporous TiN structure with high surface area and excellent electrical conductivity was fabricated for application as a catalyst support in proton exchange membrane fuel cell (PEMFC). Pt nanoparticles were then uniformly deposited on the TiN porous support by wet chemical reduction. The performances of PEMFC using Pt@TiN electrodes were evaluated by a single cell test station. The membrane electrode assembly using Pt@TiN for both anode and cathode exhibited 70%–120% higher specific power densities than that of commercial E-Tek due to higher electrical conductivity and porosity of the catalyst support and higher Pt utilization efficiency.     

Development of direct methanol alkaline fuel cells using anion exchange membranes

Research into the development of direct methanol alkaline fuel cell (DMAFC) using an anion exchange polymer electrolyte membrane is described. The commercial membrane used had a higher electric resistance, but a lower methanol diffusion coefficient than Nafion^® membranes. Fuel cell tests were performed using carbon supported Pt catalyst, and the effect of temperature, methanol concentration, methanol flow rate, air pressure and Pt loading were investigated. It was found that the cell performance improved drastically with a membrane assembly electrode (MEA) which did not include the gas diffusion layer on the anode, because of lower reactant mass transfer resistance. To give suitable cathode performance, humidification of the air and a subtle balance between the air pressure and water transport is required.     

Evaluation of electrochemical performance for surface-modified carbons as catalyst support in polymer electrolyte membrane (PEM) fuel cells

The electrochemical performance of platinum (Pt) catalyst deposited on various functionalized carbon supports was investigated and compared with that of a commercial catalyst, Pt on Vulcan XC-72 carbon. The supports employed were graphitic or amorphous with a wide range of surface areas. Cyclic voltammetry (CV) and rotating disk electrode (RDE) studies on the supported catalysts indicated equivalent platinum catalyst activities. Fuel cell performance was determined for membrane electrode assemblies (MEA) fabricated from the supported catalysts. The use of high surface area supports did not necessarily translate into a higher electrochemical utilization of platinum. Electrochemical impedance spectroscopy (EIS) measurements indicated lower ohmic losses for low surface area carbon MEAs. This is explained by the supported catalyst electrode microstructures and their intrinsic resistivities. Correlation of all data indicates that for low surface carbons, nature of the support does not significantly affect the Pt catalytic activity. The influence of the support is more critical when high surface area carbons are used because of the vastly different electrode morphology and resistivity.     

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.     

Influence of anion ionomer content and silver cathode catalyst on the performance of alkaline membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs)

Alkaline membrane electrode assemblies (MEAs) were fabricated by a dry spraying method in order to evaluate and improve their performance. I–V tests indicated that the performance of alkaline direct methanol fuel cells (DMFCs) deeply depends on the ionomer contents of MEAs. MEA with 45.4% mass ionomer content showed the highest performance when non-alkaline (MeOH (1 M)) and alkaline (MeOH (1 M), NaOH (0.5 M)) fuels were used. When alkaline fuel was used, the anode and cathode performances of MEAs were also measured. The ionomer content has been shown to contribute ohmic polarization of the anode and diffusion polarization of the cathode. Furthermore, the performance of MEA with an Ag cathode catalyst was characterized. The Ag cathode catalyst was demonstrated to be a promising alternative to a Pt cathode catalyst because of its tolerance for methanol crossover.     

Non-platinum cathode catalysts for alkaline membrane fuel cells

Hydrogen–oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm⁻² using H₂ and O₂ gases.     

Modified equations for the performance of oxygen reduction reaction catalyst from rotating disk electrode to membrane electrode assembly

Kinds of electrocatalysts developed for the cathode of Polymer electrolyte membrane fuel cell (PEMFC) show more outstanding performance when loading on rotating disk electrode (RDE) than assembling in the membrane electrode assembly (MEA), and this phenomenon has not be explained quantitatively yet. Here we developed the Butler-Volmer equation further on the base of the detailed disassembly of the elemental reaction processes that occurring on the surface of the cathodic catalyst and in the MEA. These analytical equations quantifiably indicate how the catalyst's structural parameters and electrode's microstructural parameters to influence the performance of catalyst. Further analysis shows there may be more than one order of magnitude for the PEMFC's current density improvement when using the traditional catalyst like Pt/C, after optimizing the structure of catalytic layer. Meanwhile, the increasing hydrogen permeation not only lower the open-circuit voltage but also cause the whole polarization curve moving down, which means an attenuation of PEMFC's lifetime. These equations shown in this work are established on the strict deduction of mathematics and physics and will give the new guidance for evaluating and improving the performance of electrocatalysts when assembling in MEA.     

High performance alkaline-acid direct glycerol fuel cells for portable power supplies via electrode structure design

Alkaline-acid direct glycerol fuel cells (AA-DGFC) were fabricated and primarily proven to be used as portable power generating devices. Pt/C catalyst was used as electrocatalyst for both anode and cathode. The optimal operating condition for cathode was firstly tested. Then the effects of types of backing and microporous layer on the cell performance and stability were investigated to obtain the optimal electrode structure. The cell performance was determined by using both chronoamperometry technique at a constant voltage of 0.4 V, and cell polarization with impedance measurement. The maximum peak power density obtained from the cell was 375 mW cm⁻² and the highest average current density discharged from the cell was 451 mA cm⁻². Non-wetproof carbon cloth is suitable as the backing layer for both the anode and cathode. Although MPL did not directly affect the cell performance, it greatly improved stability of the current discharged during chronoamperometric test. The cathode favors hydrophilic MPL, while hydrophobic MPL was preferred on the anode.     

Synthesis and characterization of Cu@Pt/C core-shell structured catalysts for proton exchange membrane fuel cell

A Cu@Pt/C catalyst was synthesized by a two-step reduction method using Vulcan XC-72R as the supporting material. Physical and electrochemical techniques were applied to investigate the structure and performance of the catalyst. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations showed that the catalyst has a core-shell structure, the distribution of the catalyst particles is quite uniform, and the particle size ranges from 5 to 6 nm. Cyclic voltammetry (CV) and rotating disk electrode (RDE) tests confirmed the high performance of the Cu@Pt/C catalyst with the atom ratio Cu: Pt of 2.73: 1, making it a promising low-Pt catalyst for proton exchange membrane fuel cell (PEMFC).     

Effect of anion exchange ionomer content on electrode performance in AEM water electrolysis

Anion exchange membrane water electrolysis (AEMWE) has acquired substantial consideration as a cost-effective hydrogen production technology. The anion ionomer content in the catalyst layers during hydrogen and oxygen evolution reaction (HER and OER) is of ultimate significance. Herein, an in-situ half-cell analysis with reference electrodes was carried out for simultaneous potential measurements and identification of the influence of the anion exchange ionomer (AEI) content on anode and cathode performance. The measured half-cell potentials proved the influence of AEI content on the catalytic activity of HER and OER, which was supported by the rotating disk electrode (RDE) measurements. Cathode overpotential of Ni/C was not negligible and more affected by the AEI content than anode with the optimized AEI content of 10 wt% while NiO anode OER overpotential was independent of the AEI content. For the same AEI content, PGM catalysts showed higher electroactivity than Ni-based catalysts for HER and OER and the cathode catalyst's intrinsic activity is of high importance in the AEM electrolysis operation. Post-mortem analysis by SEM mapping of both AEI and catalyst distributions on the electrode surface showed the effect of AEI loading on the catalyst morphology, which could be related to the electrode performance.     

The Pt–Co alloying effect on the performance and stability of high temperature PEMFC cathodes

High temperature (HT) PEMFC technology offers a number of advantages over its low temperature counterpart, including high tolerance to fuel impurities, system simplifications and generation of high-quality waste heat. Nevertheless, the operating temperature and the presence of phosphoric acid necessitate the use of high amounts of platinum metal at the electrodes, especially the cathodic one. In this work, we report the facile preparation of a Pt–Co alloy supported on multi-wall carbon nanotubes. Using the rotating disk electrode method in HClO₄, the activity of this catalyst towards the oxygen reduction reaction, as well as its tolerance to phosphoric acid is evaluated. A comparison is made with two electrocatalysts with similar characteristics (support, nanoparticle size and spatial distribution), where one is based on Pt and the other is a physical mixture of the aforementioned metals (Pt and Co). The superior behavior of the alloyed electrocatalyst urged its electrochemical characterization in-situ, at the cathode of a HT-PEMFC, where performance and, very importantly, stability are thoroughly evaluated and discussed. A comparison with a commercial state-of-the-art electrocatalyst shows the potential to decrease the metal loading of HT-PEMFC electrodes without compromising performance.     

Perovskite-type oxides La1−xSrxMnO3 for cathode catalysts in direct ethylene glycol alkaline fuel cells

Carbon-supported La_1−xSr_xMnO₃ (LSM/C) was prepared by reversible homogeneous precipitation method, and its catalytic activities for oxygen reduction under the existence of ethylene glycol (EG) were investigated by using rotating disk electrode. LSM/C exhibited the high activity for oxygen reduction irrespective with the presence of EG, indicating that EG is not oxidized by LSM/C at the cathode side in the present system. Consequently, LSM/C can serve as a cathode catalyst in alkaline direct alcohol fuel cells with no crossover problem. Performance test for fuel cells operation also supported these results and showed cathodic polarization curves were not affected by the concentration of EG supplied to anode even at 5 mol dm⁻³.     

The effect of functionalised multi-walled carbon nanotubes in the hydrogen electrooxidation reaction in reactive currents impurified with CO

The present article investigates the tolerant effect exerted by a functionalised multi-walled carbon nanotube (MWCNT) support compared with the Vulcan XC-72 support for a nanoparticulate Pt catalyst. The negative effect produced in the hydrogen oxidation reaction (HOR) by the presence of a Pt contaminated with high CO coverage was analysed. This investigation was conducted using a rotating disk electrode (RDE) and a single cell with membrane electrode assemblies (MEAs) with loads of 0.3 mg Pt/cm² for the anode and 0.6 mg Pt/cm² for the cathode at various poisoning times. To this end, polarisation curves were performed, and electrochemical impedance spectroscopy (EIS) measurements were analysed. In addition, the recovery of the poisoning/de-poisoning process was studied. The –OH groups anchored to the MWCNT support exert a protective effect on the Pt nanoparticles, making the catalyst more efficient in a PEMFC fed with H₂ + CO.