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In this paper, an extensive characterisation of a range of carbon blacks (CB) with similar surface area but different surface chemistry is carried out by flow calorimetry, Raman spectroscopy, dynamic water vapour sorption, instrumental gas analysis, nitrogen adsorption/desorption and high potential chronoamperometry. Using these carbon materials as supports, Pt/CB electrocatalysts are prepared by microwave‐assisted polyol‐mediated synthesis in gram scale. Structural, morphological and electrochemical properties of the prepared electrocatalysts are evaluated by X‐ray diffraction, transmission electron microscopy, rotating disc electrode and in situ fuel cell characterisation of the corresponding membrane–electrode assemblies. The obtained results allow to establish a relationship between surface chemistry and electrochemical properties useful for the design of Pt/C catalyst layers with high performance and stability. [ABSTRACT FROM AUTHOR]

A model-based impedance spectroscopy is used to determine proton conductivity, oxygen transport parameter, double layer capacitance and oxygen reduction reaction (ORR) Tafel slope in the Fe-N-C cathode catalyst layer (CCL) of a PEM fuel cell. Experimental spectra of two cells differing by the membrane thickness only are processed using a physics-based model for PEMFC impedance. The spectra have been measured in the range of current densities from 25 to 800 mA cm-2. The ORR Tafel slope of both the cells shows almost linear growth with the current density. In one of the cells, the CCL proton conductivity σp strongly decays at the current density of 100 mA cm-2; this decay is accompanied by the step growth of the double layer capacitance. Other minor variations of proton conductivity and double layer capacitance with the cell current occur also in a counterphase; presumed origin of this effect is discussed. The oxygen diffusion coefficient in the cathode exhibits explosive growth with the cell current. We attribute this effect to formation of temperature and pressure gradients in the CCL due to strongly non-uniform distribution of ORR rate in the electrode. [ABSTRACT FROM AUTHOR]

We introduce a new platinum group metal-free (PGM-free) hydrogen oxidation electrocatalyst with superior performance in anodes of alkaline exchange membrane fuel cells (AEMFCs). A carbon-supported bimetallic nickel–molybdenum catalyst was synthesized by thermal reduction of transition metal precursors on the surface of a carbon support (KetjenBlack 600J). The mass-weighted activity of 4.5 A gMe−1 determined in a liquid electrolyte 0.1 M NaOH using a rotating disk electrode (RDE) technique is comparable to the value reported for Pd/C with a comparable particle size under similar conditions. This NiMo/KB catalyst was integrated in a membrane electrode assembly (MEA) using an alkaline exchange membrane and ionomer. Single AEMFC tests performed in a H2/O2 configuration resulted in a record power density output of 120 mW cm−2 at 0.5 V, the MEA was found to be durable under the conditions of potential hold of 0.7 V for 115 h. For the first time, operando X-ray computed tomography (CT) experiments were performed demonstrating liquid water formation at the PGM-free anode during cell operation, and in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and X-ray absorption spectroscopy (APXAS) were used to study the role of molybdenum in hydrogen adsorption. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a study of multi-phase flow through the cathode side of a polymer electrolyte membrane fuel cell employing an interdigitated flow field plate. A previously published model has been extended in order to account for phase change kinetics, and a comparison between the interdigitated flow field design and a conventional straight channel design has been conducted. It is found that the parasitic pressure drop in the interdigitated design is in the range of a few thousand Pa and could be reduced to a few hundred Pa by choosing diffusion media with high in-plane permeability. The additional compressor work due to the increased pressure loss will only slightly increase, and this may be offset by operating at lower stoichiometries as the interdigitated design is less mass transfer controlled, which means that the overall efficiency of the interdigitated arrangement will be higher. In the interdigitated design more product water is carried out of the cell in the vapor phase compared to the straight channel design which indicates that liquid water management might be less problematic. This effect also leads to the finding that in the interdigitated design more waste heat is carried out of the cell in the form of latent heat which reduces the load on the coolant. Finally we see that the micro-porous layer might help keep the gas diffusion layer substrate dry due to a potentially higher evaporation rate caused by a combination of the Kelvin effect and a larger specific surface area compared to the diffusion layer substrate. [Copyright &y& Elsevier]

A three-dimensional multiphase mode! that describes the liquid water flux through the porous media and into the gas flow channel of a proton exchange membrane fuel cell (PEMFC) cathode is presented. The mode! is based on the multifluid approach, thus solving one complete set of transport equations for each phase. It is used to investigate the effect of different material parameters on the predicted liquid water saturation in various layers, i.e., catalyst layer (CL), microporous layer (MPL), and gas diffusion layer (GDL). Each layer can be characterized by its porosity, permeability, and contact angle, while the Leverett function was used to describe the capillary pressure vs saturation. The irreducible saturation can be specified for each layer independent!y. An expression for the channel/GDL interface condition was developed, which accounts for the number of drop!ets per unit area at the GDL interface. Describing the different porous media by Leverett equations leads to a jump condition in saturation across each interface. In accordance with previous studies it is found that the MPL remains at a low saturation level, while the CL might become flooded depending on the fraction of hydrophilic pores. Under-the-land compression leads to an increased level of flooding compared to the channel section. [ABSTRACT FROM AUTHOR]

A family of novel carbon materials with intermediate surface area and varying morphology and surface chemistry were used to prepare Pt/C catalysts by two different preparation procedures; a chemical impregnation method and a microwave-assisted polyol method. The catalysts were thoroughly characterized, and their electrochemical performance and stability were investigated with rotating disc electrode (RDE) cyclic voltammetric (CV) measurements. The intermediate-surface-area carbon supports gave catalysts with much greater support stability than a widely used standard catalyst. The novel catalysts had lower electrochemical surface area than the reference, but their specific electrocatalytic activity towards the oxygen-reduction reaction (ORR) was much higher, and some of them also featured higher mass-specific ORR activity than the reference. The series of catalysts prepared by the microwave-assisted polyol method featured smaller Pt nanoparticles and higher activities than those prepared by impregnation. On the other hand, the impregnated catalysts showed better durability of the Pt particles. The most promising catalysts were selected and elaborated in further optimized preparation procedures to obtain quantities sufficient for their use in proton-exchange membrane fuel cells (PEMFCs). [ABSTRACT FROM AUTHOR]