Probing Sulfur Contamination Mechanisms in Solid Oxide Fuel Cells Using Operando Methods

Abstract

Solid oxide fuel cells (SOFCs) are high temperature combined heat and power systems that are fuel flexible and offer an attractive alternative to traditional proton exchange fuel cells. However, sulfur contaminants found in bio-derived and logistics fuels can severely hinder conversion efficiency due to interactions between sulfur and the nickel-based anodes commonly used in SOFCs. Identifying themechanisms responsible for sulfur degradation of SOFCs and their dependence on operating conditions would help in improving device performance and durability. In this study, the effects of sulfur contamination and the subsequent degradation of SOFCs operating on methane between 600° – 800° C are characterized using chronocoulometry, electrochemical impedance spectroscopy, and operando optical methods. The latter include near infrared thermal imaging as well as spectroelectrochemical vibrational Raman and IR emission spectroscopies. The results indicate that sulfur contaminants competitively inhibit methane catalytic and electrocatalytic sites and induce irreversible changes of the Ni-YSZ anode permanently perturbing their catalytic and electrocatalytic function. Studies are performed to determine if sulfur degradation is reversible and how it depends on fuel composition and temperature.