Quasielastic neutron scattering of hydrated BaZr(0.90)A(0.10)O(2.95) (A = Y and Sc)

Proton motions in hydrated proton conducting perovskites BaZr(0.90)A(0.10)O(2.95) (A = Y and Sc) have been investigated using quasielastic neutron scattering. The results reveal a localized motion on the ps time scale and with an activation energy of similar to 10-30 meV, in both materials. The temperature dependence of the total mean square displacement of the protons shows an onset of this motion at a temperature of about 300 K. The low activation energy, much lower than the activation energy for the macroscopic proton conductivity, suggests that this motion is not the rate-limiting process for the long-range proton diffusion, i.e. it is not linked to the two materials significantly different proton conductivities. In fact, a comparison of the QENS results with density functional theory calculations indicates that for both materials the observed motion may be ascribed to intra-octahedral proton transfers occurring close to a dopant atom. (C) 2008 Elsevier B.V. All rights reserved

Non-Noble intertransition binary metal alloy electrocatalyst for Hydrogen oxidation and Hydrogen evolution

Metastable and amorphous intertransition metal alloys of CuW are shown to catalyze both the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). The constituent metals exhibit poor activity. The results are consistent with ab initio calculations predicting HER activity for Cu overlayers on W and with the observed changes of the density of states (DOS) at the Fermi level associated with CuW alloy formation. Two maxima in the HER activity are observed as a function of composition corresponding a bulk metastable phase at 80 at % Cu and a second at 50 at % Cu. The alloy at 50 at % also corresponds to a maximum in the HOR activity, whereas the phase at 80 at % Cu is not HOR active. The latter phase is shown to be oxygen-covered at the HOR potential, explaining its inactivity. These results highlight the possibilities of developing non-noble metal alloy catalysts for hydrogen fuel cell

Atomistic modeling of electrocatalysis: Are we there yet?

International audienceElectrified interfaces play a prime role in energy technologies, from batteries and capacitors to heterogeneous electrocatalysis. The atomistic understanding and modelling of these interfaces is challenging due to the structural complexity and the presence of the electrochemical potential. Including the potential explicitly in the quantum mechanical simulations is equivalent to simulating systems with a surface charge. For realistic relationships between the potential and the surface charge (i.e., the capacity), the solvent and counter charge need to be considered. The solvent and electrolyte description are limited by the computational power: either molecules and ions are included explicitly, but the phase-space sampling is at least 10 times too small to reach convergence or implicit solvent and electrolyte descriptions are adopted which suffer from a lack of realism. Both approaches suffer from a lack of validation against directly comparable experimental data. Furthermore, the limitations of density functional theory in terms of accuracy are critical for these metal/liquid interfaces. Nevertheless, the atomistic insight in electrocatalytic interfaces allow insights with unprecedented details. The joint theoretical and experimental efforts to design non-noble hydrogen evolution catalysts are discussed as an example for the success of theory to spur and accelerate experimental discoveries. Graphical/Visual Abstract and Captio