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International audience; Architecturally designed La2−xPrxNiO4+δ (with x = 0, 0.5, 1 and 2) cathodes on the Ce0.9Gd0.1O2−δ (CGO) electrolyte have been prepared with a view to take advantage of the complimentary properties of the two extreme compositions La2NiO4+δ and Pr2NiO4+δ, i.e. the superior stability of La2NiO4+δ and the higher electronic conductivity of Pr2NiO4+δ. The design consists of stacking of two layers starting with a 3D tree-like microstructure (∼20 μm thick) over a thin dense base layer (∼100 nm) fabricated in one step by electrostatic spray deposition (ESD) and then topped by using a screen-printed (SP) current collecting layer of the same composition. X-ray diffraction confirms the formation of a complete solid solution crystallizing in a single phase orthorhombic structure with the Fmmm space group. The thermodynamic stability and polarisation resistance (Rpol) decrease by increasing the Pr content. Among the complete La2−xPrxNiO4+δ solid solutions, LaPrNiO4+δ shows the best compromise between electrochemical properties (the lowest Rpol value available in the literature for this composition, 0.12 Ω cm2 at 600 °C) and thermodynamic stability in air. Moreover, an anode supported single cell (Ni-3YSZ/Ni-8YSZ/8YSZ/CGO) including the LaPrNiO4+δ double layer electrode shows a maximum power density of 438 mW cm−2 at 700 °C.

The CO oxidation reaction on carbon-supported Pt nanoparticles (average size of 2.8 to 7.7 nm) was studied under flowing conditions at atmospheric pressure and temperatures between 300 and 353 K by coupling quadrupole mass spectrometry (QMS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The Pt loading was varied between 20 and 60 wt%. Gases diluted in He (0.5 mol%) were used together with Ar as a tracer. Reactions with CO and O2 introduced separately onto the samples were studied by QMS, applying successive step changes of the reaction mixtures. Variations in the rate of the reactions were observed and correlated with changes of the calculated coverage of the Pt surface by CO and/or O adspecies at varying steps of the experiment. The transient reaction of CO(g) with adsorbed O (Oad) was fast and mass transport-limited while that of O2(g) with adsorbed CO (COad) was sluggish. Following the same experimental procedures, FTIR spectra of adsorbed CO after varying steps were recorded, confirming the variations of COad and Oad as determined by QMS and indicating changes in the CO distribution over varying types of Pt surface sites. The influence of the adlayer composition (co-adsorption of COad and Oad), the particle size/structure and some possible surface reconstruction effects on the CO oxidation rate were evidenced and discussed. The structure of the Pt nanoparticles supported on carbon appears as an important factor for the efficiency of the so-called O2 bleeding as a CO mitigation strategy in polymer electrolyte membrane fuel cells.

In this paper, based on a multiscale modelling framework, we focus on understanding the impact of CO adsorption on the intrinsic stability properties of PtxCoy nanoparticles under PEMFC anode operating conditions. First, CO adsorption effect on PtxCoy has been studied by using Monte Carlo (MC) simulation. Then, the MC results are coupled with an ab initio based kinetic model to simulate the effect of CO poisoning on the activity and durability of the PtxCoy nanoparticles as HOR catalysts. The results are compared with simulations carried out with pure Pt, where potential self-oscillatory behaviour is detected and experimentally confirmed. The PtxCoy HOR activity and stability reveals to be strongly dependent on the nanoparticle size and composition. For some nanoparticle sizes, simulations show that PtCo nanoparticles provide better CO tolerance than Pt3Co. CO adsorption on PtCo slows down Co dissolution in short-term operation. However, this effect is overcome by the increase of the anode potential due to CO adsorption. Thus, CO adsorption enhances Co dissolution in long-term operation. Due to this Co dissolution, the HOR activity of PtCo degrades faster than Pt3Co in long-term operation.

In this paper we discuss a comprehensive physical-based model of the PEMFC materials degradation allowing predicting the MEA durability as function of the operation conditions, initial material loadings and electrodes microstructure. The approach, build within a modular multiscale non-equilibrium thermodynamics framework, couples atomistic-based descriptions of catalyst contamination/oxidation/dissolution/ripening, dissolved catalyst migration in the ionomer, C catalyst-support corrosion and chemical PEM degradation, with the degradation-induced nano/microstructural and transport properties (of reactants and charges) evolution. By describing the feedback between the instantaneous performance and the material aging phenomena, the model provides new insights on the competition between the different degradation processes under automotive-operating conditions. The predictive capabilities of our approach are illustrated in this paper through four applicative examples: 1) PtxCoy catalysts degradation 2) competition of PEM and cathode C degradation 3) synergies between anodic CO contamination and PEM and cathode C degradation, and 4) synergies between Pt and C degradation.

A nanostructured three-dimensional (3D) microbattery has been produced and cycled in a Li-ion battery. It consists of a current collector of aluminum nanorods, a uniform layer of 17 nm TiO(2) covering the nanorods made using ALD, an electrolyte and metallic lithium counter electrode. The battery is electrochemically cycled more than 50 times. The increase in total capacity is 10 times when using a 3D architecture compared to a 2D system for the same footprint area.

ENERGIE+KIC:VBE:PGE; CO adsorption on carbon-supported Pt nano-particles under operando conditions was studied by quadru-pole mass spectrometry and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). The Pt catalyst was also studied by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). It was shown by HRTEM and XPS that Pt nanoparticles can be fully reduced by H-2 at room temperature instead of by conventional high-temperature treatment. The Pt dispersion was determined by XRD, HRTEM, and CO chemisorption techniques with an excellent agreement among them. The room-temperature H-2/O-2 titration method was also used, but if assuming H/Pt-s = O/Pt-s = 1, it led to the underestimation of the dispersion compared to the other techniques. The existence of adsorption sites inaccessible to H-2 (or O-2) but accessible to CO because of a stronger interaction with Pt was proposed to explain the results. It was also concluded that H/Pt-s was lower than unity (H/Pt-s = 0.72) and, as a major consequence, that Pt nanoparticles with 2.7 nm diameter still have a bulk-like behavior in contrast with what was reported in the literature for 1 nm Pt particles. CO adsorption on Pt/C at 298 K after H-2 treatment was studied by operando DRIFTS. The C-O stretching vibration (nu CO) bands were ascribed to CO adsorbed on Pt surface at (111)-terrace, (100)-terrace, edge, and kink sites in linear and bridge forms. An unexpected nu CO band at 1703 cm(-1) was observed upon CO adsorption and tentatively attributed to CO on surface Pt sites interacting through its oxygen end with the carbon support. It was also shown that the adsorption of CO and H-2 in successive repeated steps was necessary to reach a stable state of the adsorbed CO phase. Possible reconstruction of Pt nanoparticles at room temperature during this process is discussed.

Based on a multiscale modeling framework, we focus on understanding the impact of CO adsorption on the intrinsic stability properties of PtxCoy nanoparticles under PEMFC anode operating conditions. Firstly, CO adsorption effect on PtxCoy has been studied by using Monte Carlo (MC) simulation. Then, the MC results were coupled with a non-equilibrium thermodynamics kinetics model (MEMEPhys®) to simulate the effect of CO poisoning on the activity and durability of PtxCoy nanoparticles as HOR catalysts. The results are compared with simulations carried out on Pt, where potential self-oscillatory behaviour is observed and experimentally confirmed. The PtxCoy HOR activity and stability properties reveal to be strongly dependent on the nanoparticle size and composition. For certain nanoparticle sizes, simulations show that PtCo nanoparticles provide better CO tolerance than Pt3Co. However, the CO tolerance of PtCo degrades faster than that of Pt3Co in long-term operation. From both modeling and experimental approaches, it is demonstrated for the first time that this observation is due to the fact that CO adsorption enhances Cobalt dissolution.

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