Redox-Induced Self-Modification of Cermet Anodes of Ni–CeO₂-Based Oxide for Solid Oxide Fuel Cells

Abstract

Recently, the strong chemical interaction between Ni and GDC (Gd 2 O 3 −CeO 2 ) was reported for the cermet anode of Ni−GDC in solid oxide fuel cells (SOFCs); 1 CeO 2 species migrated on the Ni surface after exposure to the reducing atmosphere. This surface modification of nickel affected the catalytic properties for carbon deposition and CO adsorption. Generally, such a chemical interaction is promoted by the oxidation-reduction (redox) treatment. In this study, then, the influence of redox treatment on catalytic and electrochemical properties of Ni-GDC cermets was investigated in detail to establish a new design concept of anodes. The Ni−GDC cermet subjected to the redox treatment showed high tolerance to carbon deposition. Furthermore, the redox treatment did not affect the mechanism of electrochemical hydrogen oxidation in humidified hydrogen atmospheres. We also demonstrated the stable power generation of the single cell employing the optimized Ni−GDC anode at 1000 • C in a wet methane atmosphere with a steam to carbon ratio of 0.1.

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

“…ALD is ideal for coating the Ni phase with a thin overcoat to suppress the agglomeration and oxidation of the underlying Ni [111]. A similar approach would seem to be ideal for depositing ceria to prevent carbon formation [112].…”

Redox stability of metal-supported fuel cells with nickel/gadolinium-doped ceria anode

“…Furthermore, the FIB-SEM investigation identified the accelerated coarsening of Ni in contact with the GDC as one possible reason for electrolyte delamination. Several authors [35,45] have reported stronger Ni coarsening in the presence of the GDC due to strong interfacial interaction. This must also be considered during the processing of Ni/GDC anodes [13].…”

“…These effects lead to increased tortuosity of the Ni and YSZ, while the tortuosity of the pores decreases. The redox behavior of Ni/GDC anodes has been less reported in the literature so far [15,35,36]. GDC is an attractive material for the ceramic backbone of SOFCs, since it contributes to the electrochemical performance of the anode.…”

“…A clear increase of electrochemical performance results from the Ni/YSZ anodes being replaced by Ni/GDC anodes [13,40]. Furthermore, GDC significantly improves the tolerance against sulfur and carbon deposition if the cell is operated with H2S containing fuels or hydrocarbons, respectively [35,41]. If applying GDC as a ceramic backbone, certain properties of the ceria phase must be considered.…”

“…This effect has a clear influence on the processing of Ni/GDC anodes and accelerates Ni coarsening during sintering, especially at temperatures above 1000 °C [13]. However, in the case of redox cycling of the Ni/GDC anodes, the Ni surface becomes increasingly covered with GDC in line with the increasing number of redox cycles [35]. Under certain conditions, this effect might lead to improved electrochemical performance due to an improvement of the GDC-Ni contact area and an increase of the active length of the TPBs.…”