Oxidation of H₂, CH₄, and CO Molecules at the Interface between Nickel and Yttria-Stabilized Zirconia: A Theoretical Study Based on DFT

Abstract

Activation of fuel molecules (H2, CH4, CO) at the anode triple phase boundary (TPB) of a solid oxide fuel cell, modeled by a Ni (nickel)/YSZ (yttria-stabilized zirconia)/fuel interface is investigated using density functional theory. We demonstrate that, by employing ab initio calculations, it is possible to elucidate the mechanisms of electronic charge transfer and current generation as a result of electrochemical oxidation of fuel in the anode TPB. Moreover, we show that an oxygen-enriched YSZ surface (YSZ+O) of the Ni/YSZ cermet is significantly less active toward oxidation of fuel molecules than an oxygen-enriched YSZ surface in the absence of Ni, which is explained by partial saturation of the valence of an extra oxygen atom of the Ni/YSZ cermet. On the other hand, the chemical activity of the Ni part of the cermet is close to that of the infinite Ni surface, even in the proximity to the YSZ. The YSZ+O surface of the cermet is found generally inert, as adsorption of H2 and CH4 is associated with high kinetic barriers, whereas CO adsorption is a more favorable, although endothermic reaction. The oxidation of H2 and CO on Ni after oxygen spillover from the oxide is exothermic, and CH4 oxidation is mildly endothermic. It is also shown that transfer of hydrogen atoms from Ni to YSZ (hydrogen spillover reactions) with subsequent water formation is another possible scenario of hydrogen oxidation on the YSZ+O surface.

Chemical Descriptors of Yttria-Stabilized Zirconia at Low Defect Concentration: An ab Initio Study

“…YSZ is a key component of the SOFC anode where it forms an interface with a catalytic metal and a gas phase. The interface region is referred to as the anode triple phase boundary (TPB) [3][4][5][6][7][8] . There is a growing interest in developing predictive models of the physical and chemical properties of YSZ and its surfaces in order to model the chemistry occurring at the anode TPB.…”

First-principles study of oxygen coverage effect on hydrogen oxidation on Ni(111) surface

“…Most of the papers are discussed on the dissociation of H 2 O to OH and H [10][11][12][13]16,22], as a one of the steps of steam reforming reaction on Ni surface. Limited papers are reported about the oxidation reaction on Ni surface assuming the SOFC anode [21,[31][32][33][34][35]. However, the chemical reaction analysis on the clean Ni surface is main target in the previous papers.…”

Computational Investigation of the Thermochemistry and Kinetics of Steam Methane Reforming Over a Multi-Faceted Nickel Catalyst

“…As a result, researchers have been engaged in the development of membrane reactors capable of the in situ separation of the CO 2 (g) and H 2 (g) products, allowing for subsequent sequestration of the carbon dioxide [3][4][5]. In addition to traditional hydrogen production, the kinetics of the SMR and WGS reactions are an active area of research with regard to internal reforming in solid oxide fuel cells [6][7][8]. Historically, nickel is the preferred SMR catalyst because of its reasonably high activity and affordability relative to noble metal catalysts [9].…”