Quantum-Chemical Analysis of the Mechanism of Degradation of Binary Platinum Nanoclusters with Sulfur-Containing Compoun
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QUANTUM-CHEMICAL ANALYSIS OF THE MECHANISM OF DEGRADATION OF BINARY PLATINUM NANOCLUSTERS WITH SULFUR-CONTAINING COMPOUNDS S. А. Kornii,1,2 V. I. Pokhmurs’kyi,1 and N. R. Chervins’ka1
UDC 544.636.23:544.653.22:620.194.23
We propose a quantum-chemical model of poisoning of binary Pt 42 Me13 platinum nanoclusters (where Me is a transition metal, namely, Fe, Co, or Ni) with core-shell structure by hydrogen sulfide and sulfur dioxide in media of low-temperature fuel cells. This model is based on the evaluation of the adsorption characteristics of interaction of H 2S and SO 2 molecules with the surfaces of nanoclusters. It is shown that their susceptibility to the formation of strong chemisorption bonds with H 2S and SO 2 molecules depends on the type of nanocluster core and the sites of adsorption on their surfaces. By using the quantum-chemical method of density functional, we establish the regularities of influence of the cores of binary nanoclusters of transition metals Fe, Co, or Ni on the geometric and energy characteristics of the adsorption of molecules. We also propose the mechanism of interaction of H 2S and SO 2 molecules with binary platinum nanoclusters based on the changes in the electronic properties of the surface platinum atoms or in the distribution of active adsorption centers on the surface of nanoclusters depending on the type of the core. The accumulated results confirm the prospects of the density functional method in the theoretical evaluation of the influence of chemical composition and the structure of binary nanoparticles on their properties in the reactions of low-temperature fuel cells. Keywords: density functional method, platinum, binary nanoclusters, geometric structure, hydrogen sulfide, sulfur dioxide, adsorption energy, energy activity.
In the production of catalytic electrodes of low-temperature fuel cells, it is customary to use binary platinum nanoparticles of the PtMe type (where Me is a transition metal, namely, Cr, Fe, Co, or Ni) with an aim to decrease their cost. It is known [1] that the catalytic activity of these nanoparticles can be higher than the activity of pure metallic particles. However, in the case of application of hydrogen obtained as a result of the conversion of hydrocarbons, the period of efficient operation of nanocatalyst becomes much shorter as a result of its poisoning by the admixtures of carbon oxide and sulfur-containing compounds [hydrogen sulfide ( H 2S ) and sulfur dioxide ( SO 2 )]. In other words, despite quite high catalytic characteristics of binary nanoparticles or nanoclusters, their stability and corrosion resistance can be insufficient for long-term operation. Even insignificant admixtures of these compounds remaining in the gases after their purification, poison the platinum anode, block its active centers, and decelerate the reaction of hydrogen oxidation. If we analyze the literature data on the kinetics of hydrogen-sulfide adsorption and its oxidation on pure platinum [2–7] and its binary alloys [8, 9], then we can make the following conclu
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