Low-Temperature Fuel Cells Research Articles

Mixed Reactant Low Temperature Fuel Cells: The Swiss-Roll Cell Design and Selective Electrocatalysts

Eliminating the proton exchange membrane (PEM) together with the platinum-based anode and cathode catalysts and replacing the bulky bipolar plates with lighter and flexible alternatives, would significantly improve the economic outlook of low temperature fuel cells operated with liquid fuels. To address the afore-mentioned issues of PEM fuel cells, at the University of British Columbia we have developed a novel mixed reactant fuel cell design referred to as the Swiss-roll cell, fed with a two-phase mixture of liquid fuel and air (or oxygen) [1-5]. Here, a research progress review is presented related to both selective electrocatalysis and Swiss-roll cell engineering applied to two alkaline fuel cell systems: sodium borohydride – oxygen and sodium borohydride – nitrous oxide, respectively. On the anode, the borohydride electro-oxidation reaction is a complex, up to eight electron transfer process, with possibly competing hydrogen evolution generated by either faradaic (i.e., electrocatalytic) or non-faradaic (i.e., thermocatalytic) pathways. Experimental results correlated with density functional theory modelling predictions are discussed focused on the borohdyride electro-oxidation mechanism on catalysts such as: Pt, Au and Os. On the cathode side, in case of the oxygen reduction reaction (ORR) in alkaline media the comparative performance of gas diffusion electrodes with electrocatalysts such as MnO2, Ag and Fe-aminoantypyrine (Fe-AAPyr) is presented. For nitrous oxide reduction, the electrode kinetics on Pd and Pt electrocatalysts are compared. It is shown that the selective electrocatalyst discovery combined with cell electrochemical engineering innovations enables significant improvements in the power output, reaching 250 mW/cm2 for the membrane-free Swiss-roll mixed-reactant direct borohdyride fuel cell operated at 50 0C and near atmospheric pressure using non-platinum anode and cathode catalysts.

Selective Hydrogen Oxidation Catalyst for Reduced Startup/Shutdown Degradation in Low Temperature Fuel Cells

While the durability of proton exchange membrane (PEM) fuel cells in automotive applications has been improved significantly over the past decade, the durability of the catalysts and the catalyst supports during transient operating conditions is still a critical issue. One of them is the carbon support corrosion during fuel cell startup and shutdown (SUSD) cycles [1], for which various mitigations strategies have been considered, based either on system control approaches or materials-based solutions [2, 3, 4]. A promising approach would be the use of a selective anode catalyst, i.e., with high activity for the hydrogen oxidation reaction (HOR) and low activity for the oxygen reduction reaction (ORR) [5]. Such a catalyst would eliminate the ORR on the anode electrode during a H2/air-front event (i.e., an SUSD event) and thus remove the source for the transient excursions of the cathode electrode to high potentials during SUSD. In this study, we present a promising selective anode catalyst based on iridium. Iridium exhibits not only very high HOR activity (only »3 times lower than Pt [6]), but also has significantly reduced ORR activity compared to Pt. The much lower ORR activity of Ir compared to Pt is shown in Figure 1, where the same noble-metal loading results in a >200 mV lower cell voltage for the ORR on Ir compared to Pt. On the other hand, H2-pump experiments showed that the HOR losses for the low-loaded Ir catalyst in Figure 1 only amounted to 14 mV losses at 1.5 A/cm2), in good agreement with theoretical calculated HOR losses [6]. Therefore, Ir shows promise as a possible selective anode catalyst, which might lower SUSD degradation. Figure 1. H2/O2 polarization curves recorded in in 50cm2 cell of MEAs with different cathode catalysts (20wt% Ir/C red line, 20wt% Pt/C black line) adjusted to 0.1 mgmetal/cm2. anodes based on 0.4 mgPt/cm2 using 50wt%Pt/C). Other conditions: stoich.=2/9.5; 150kPaabs, 80oC; RHC=RHA=66%. In this study we will show that replacing the conventional Pt/C catalyst with Ir/C at the anode electrode, the SUSD degradation rate can be reduced by a factor of 3 compared to Pt/C- based anodes.

(Invited) Mass Transport and Electrocatalysis: Experimental Techniques for Determining the Performance of Low Temperature Fuel Cell Electrocatalysts

Gases are important reactants in low temperature fuel cells, comprising both the fuel (hydrogen) in many systems and the oxidant (oxygen in air) in most systems. The fast transport of these reactants through the gas phase provides a problem in accurately assessing the performance of electrocatalysts over the relevant potential range of operation. This comes about because most electrochemical methods involve provision of reactant dissolved in an electrolyte, and mass transport through a condensed phase is orders of magnitude slower than through the gaseous phase. In this paper, we consider the different approaches that can be used to determine the electrocatalytic performance of test fuel cell catalysts using liquid electrolytes, and assess how closely the different approaches mimic the mass transport conditions in a low temperature PEFC. In principle, we can adopt two different approaches, we can either (a) change (in a defined way) the electron transfer kinetics of our electrochemical reaction through changing the temperature, or poisoning our catalysts; or (b) we can increase mass transport of reactant to the electrode. In the latter case, our choices include either decreasing our measurement time (fast voltammetry); increasing convection in our system (Rotating disk, Wall-Jet, channel flow, etc); or change the geometry of our system (e.g. ultra microelectrode, floating electrode etc). There is a tradeoff between accuracy of results and ease of use, leading to some significant discrepancies in the literature.

Porous Carbon Materials for Elements in Low-Temperature Fuel Cells

Abstract The porosity, distribution of pores, shape of pores and specific surface area of carbon materials were investigated. The study of sintered graphite and commercial carbon materials used in low-temperature fuel cells (Graphite Grade FU, Toray Teflon Treated) was compared. The study covered measurements of density, microstructural examinations and wettability (contact angle) of carbon materials. The main criterion adopted for choosing a particular material for components of fuel cells is their corrosion resistance under operating conditions of hydrogen fuel cells. In order to determine resistance to corrosion in the environment of operation of fuel cells, potentiokinetic curves were registered for synthetic solution 0.1M H2SO4+ 2 ppmF-at 80°C.

Recent Advances in Carbon Supported Metal Nanoparticles Preparation for Oxygen Reduction Reaction in Low Temperature Fuel Cells

The oxygen reduction reaction (ORR) is the oldest studied and most challenging of the electrochemical reactions. Due to its sluggish kinetics, ORR became the major contemporary technological hurdle for electrochemists, as it hampers the commercialization of fuel cell (FC) technologies. Downsizing the metal particles to nanoscale introduces unexpected fundamental modifications compared to the corresponding bulk state. To address these fundamental issues, various synthetic routes have been developed in order to provide more versatile carbon-supported low platinum catalysts. Consequently, the approach of using nanocatalysts may overcome the drawbacks encountered in massive materials for energy conversion. This review paper aims at summarizing the recent important advances in carbon-supported metal nanoparticles preparation from colloidal methods (microemulsion, polyol, impregnation, Bromide Anion Exchange…) as cathode material in low temperature FCs. Special attention is devoted to the correlation of the structure of the nanoparticles and their catalytic properties. The influence of the synthesis method on the electrochemical properties of the resulting catalysts is also discussed. Emphasis on analyzing data from theoretical models to address the intrinsic and specific electrocatalytic properties, depending on the synthetic method, is incorporated throughout. The synthesis process-nanomaterials structure-catalytic activity relationships highlighted herein, provide ample new rational, convenient and straightforward strategies and guidelines toward more effective nanomaterials design for energy conversion.

Boosting performance of low temperature fuel cell catalysts by subtle ionic liquid modification.

High cost and poor stability of the oxygen reduction reaction (ORR) electrocatalysts are the major barriers for broad-based application of polymer electrolyte membrane fuel cells. Here we report a facile and scalable approach to improve Pt/C catalysts for ORR, by modification with small amounts of hydrophobic ionic liquid (IL). The ORR performance of these IL-modified catalysts can be readily manipulated by varying the degree of IL filling, leading to a 3.4 times increase in activity. Besides, the IL-modified catalysts exhibit substantially enhanced stability relative to Pt/C. The enhanced performance is attributed to the optimized microenvironment at the interface of Pt and electrolyte, where advantages stemming from an increased number of free sites, higher oxygen concentration in the IL and electrostatic stabilization of the nanoparticles develop fully, at the same time that the drawback of mass transfer limitation remains suppressed. These findings open a new avenue for catalyst optimization for next-generation fuel cells.

Modeling of Low-Temperature Fuel Cell Electrodes Using Non-Precious Metal Catalysts

An electrode-scale, transport model for a proton-exchange-membrane fuel cell (PEMFC) cathode is presented. The model describes the performance of non-precious metal catalysts for the oxygen reduction reaction in a fuel cell context. Because of its relatively high thickness, emphasis is placed on phenomena occurring in the cathode layer. Water flooding is studied in terms of its impact on gas-phase transport and on electrochemically accessible surface area (ECSA). Although cathode performance in both air and oxygen are susceptible to ECSA loss, gas diffusion limitations at high current density in air are more significant. In oxygen, catalyst utilization at high current density is primarily limited by conductivity. For this reason, air fuel cell data is recommended over oxygen data for characterizing catalyst performance. Due to both ohmic and mass transport limitations, increased loading of low-cost catalysts does not necessarily lead to higher performance. Therefore, careful optimization of catalyst layer thickness is required.

Cerium Pyrophosphate-based Proton-conducting Ceramic Electrolytes for Low Temperature Fuel Cells

Acceptor-doped cerium pyrophosphates have shown significant proton conductivity of >10 -2 S cm -1 in the range of 100 - 300oC and are considered promising candidates for use as electrolytes in proton-conducting, ceramic electrolyte fuel cells (PCFCs). But, cerium pyrophosphates themselves do not have structural protons, and protons incorporate into their material bulk only as impurities on exposure to a hydrogen-containing atmosphere. However, proton incorporation and proton conduction in these materials are expected to be affected by factors such as the nature (ionic size and charge) and concentration of the aliovalent dopant, processing history (synthesis route and microstructure), and the presence of residual phosphorous phosphate P m O n ) phases. An exact understanding of these aspects has not yet been achieved, leading to large differences in the magnitude of proton conductivity of cerium pyrophosphates reported in various studies. Herein, we systematically address some of these aspects, and present an overview of factors affecting proton conductivity inacceptor-doped CeP 2 O 7 .

Three-Dimensional Nanofiber Cathode for Low Temperature and High Temperature Fuel Cells

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Durability of Low-Temperature Fuel Cell Electrocatalysts

Durability of Low-Temperature Fuel Cell Electrocatalysts

Nano-ceramic support materials for low temperature fuel cell catalysts.

Low temperature fuel cells (LTFCs) have received broad attention due to their low operating temperature, virtually zero emissions, high power density and efficiency. However, the limited stability of the catalysts is a critical limitation to the large scale commercialization of LTFCs. State of the art carbon supports undergo corrosion under harsh chemical and electrochemical oxidation conditions, which results in performance degradation of catalysts. Therefore, non-carbon materials which are highly oxidation resistant under strongly oxidizing conditions of LTFCs are ideal alternative supports. This minireview highlights the advances and scenarios in using nano-ceramics as supports to enhance the stability of catalysts, the solutions to improve electrical conductivity of nano-ceramic materials, and the synergistic effects between metal catalyst and support to help improve the catalytic activity and CO/SO2 tolerance of catalysts.

Pt–Ir Binary Electrodes for Direct Oxidation of Methanol in Low-Temperature Fuel Cells (DMFCs)

In this study, Pt–Ir binary electrodes were prepared by DC magnetron sputtering and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical techniques, and CO stripping. The effect of Ir loading in electrocatalytic activity was also explored. It was found that Ir doping up to 80 % resulted in an increase of the electrochemically active surface (EAS) area and better electrocatalytic performance toward methanol electrooxidation reaction (MOR). The above conclusion was confirmed by CO stripping experiments as well as during oxidation of methanol where the electrodes were used as anodes in a one-compartment cell. The electrode with the lower Pt loading (i.e., 20 %) exhibited better electrocatalytic activity than the pure Pt anode. The observed higher performances of Ir loading electrodes were attributed to the enhanced EAS of the Pt–Ir binary electrodes and the electronic interactions between Pt and Ir atoms.

Coaxial TiN-CNT Composites as Effective Low Temperature Fuel Cell Electrocatalyst Supports

Coaxial titanium nitride (TiN) coated carbon nanotubes (TiN-CNTs) were fabricated by a simple two-step procedure. These novel materials were utilized as Pt electrocatalyst support materials for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). By effectively coupling the unique physicochemical properties of TiN and CNTs, improved performance in comparison to commercial Pt/C was observed, indicative of the favourable catalyst-support interactions provided.

Electrochemical Oxidation of Carbon in Low Temperature Fuel Cells: Influence of the Gas Atmosphere

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Mo2C Derived Carbons Catalysts and/or Supports for Pt Metal and Pt-Ru Alloy Catalysts for Low Temperature Fuel Cells

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Carbonaceous Nanostructured Support Materials for Low Temperature Fuel Cell Electrocatalysts—A Review

Highly-dispersed platinum and platinum-based catalysts on a conductive support are commonly used as electrode materials in low-temperature fuel cells, particularly the hydrogen PEMFC and the direct methanol PEMFC. The performance and durability/stability of these catalysts strongly depend on the characteristics of the support. Catalysts supported on high surface area carbon black are widely used in low-temperature fuel cells. However, the corrosion of carbon black has been recognized as one of major causes of performance degradation and durability issues of low-temperature fuel cells under high-potential conditions. So the need for alternative supports with outstanding physical and mechanical properties to carry out the successful reaction in catalyst layer and give a longer lifetime for the electrocatalysts is inevitable. The emergence of nanotechnology and development of nanostructure materials in recent years has opened up new avenues of materials development for low-temperature fuel cells. This paper presents the performance with a variety of carbon-based nanostructured materials such as carbon nanotubes (CNT), carbon nanofibers (CNF), carbon aerogels, nanoplates of graphene, etc. So the present paper provides an overview of these nanostructured materials as low-temperature fuel cell catalyst supports. The improved characteristics of the nanostructured supports with respect to commercially used carbon black (Vulcan XC-72) and their effect on the electrochemical activity are highlighted. Additionally, it reviews the literature on the synthesis of nanostructured-supported Pt electrocatalysts for proton exchange membrane (PEM) fuel cell catalyst loading reducing through the improvement of catalyst utilization and activity. The features of each synthetic method were also discussed based on the morphology of the synthesized catalysts.

Coaxial TiN-CNT Composites as Effective Low Temperature Fuel Cell Electrocatalyst Supports

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Controllable Preparation and the Application of the Carbon-Based Materials in Low Temperature Fuel Cell

Controllable Preparation and the Application of the Carbon-Based Materials in Low Temperature Fuel Cell

Effective Use of Catalysts in Low Temperature Fuel Cells

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COMSOL Simulations for Flow Channels of Low-Temperature Fuel Cell

A multiple physical finite elements to analyze software (COMSOL Multiphysics) is employed to investigate serpentine flow channels of a small proton exchange membrane fuel cell with power 0.5W. Distributions of the oxygen flow, the liquid water, and the electric current density in three different designed flow channels are simulated and compared. Results show that increasing the channel width is conducive to increase the oxygen flow and reduce the production of liquid water. It thus enhances the electric current density. However, it will reduce the oxygen flow, produce more liquid water, and depress the current density if the channel width is decreased.