Application of solid electrolyte cells in ion pump and electrolyzer modes to promote catalytic reactions: An overview

Abstract

Solid electrolyte cells can be operated in three basic modes: fuel cell, electrolyzer and ion pump. In the fuel cell mode, a fuel such as hydrogen, CO and light hydrocarbons is electrochemically oxidized to generate power. Electrolyzer and ion pump modes, however, need application of power from an external source in order to perform the desired tasks. In this article, we present a brief overview of the studies that use an oxygen ion conducting electrolyte for catalytic applications, with two specific examples from our own studies: use of a solid electrolyte cell in the ion pump mode for alkane oxidative dehydrogenation and in the electrolyzer mode for CO2 reduction. The solid electrolyte cell assembly used in these studies consists of a button cell containing yttria-stabilized zirconia solid oxide electrolyte, a modified strontium titanate (ST) catalyst as the working electrode, i.e., anode for the ODH reaction and cathode for the CO2 reduction reaction, and a lanthanum strontium manganite (LSM) catalyst as the counter electrode.Physical properties of the titanate materials were studied using XRD, conductivity measurement and temperature-programmed oxidation with CO2. Lanthanum doped strontium titanate (La0.2Sr0.8TiO3±δ), with or without Cl, was seen to have a higher electrical conductivity compared to un-doped strontium titanate (SrTiO3). Cl doping, however, was seen to improve the electrocatalytic activity for both ODH and CO2 reduction reactions, giving higher yields of ethylene and CO compared to Cl-free La0.2Sr0.8TiO3±δ. The comparison of the catalytic and electrocatalytic ODH reactions clearly pointed out that oxygen in ionic form was more selective to ethylene than molecular oxygen at similar conversion values.