Medium-temperature electrolysis of NO and CH4 under lean-burn conditions using ytrria-stabilized zirconia as a solid electrolyte

Abstract

Electrolysis of NO and CH₄ in the presence of excess O₂ has been studied using a single-compartment reactor, constructed from yttria-stabilized zirconia (YSZ), with two palladium electrodes. The palladium electrodes were attached by an electroless plating method. Experiments were conducted between 550 and 900 °C with a mixture of 1000 ppm NO, 1000 ppm CH₄, 2% O₂, 5% H₂O and 5% CO₂ in argon at a flow rate of 50 ml min^–1. The reduction of NO to N₂ and the oxidation of CH₄ to CO₂ were promoted by applying a direct current between the two palladium electrodes. The current efficiency for the reduction of NO was about 1.5% at all measured temperatures, while that for the oxidation of CH₄ decreased from 2.7 to 0.3% with increasing temperature from 550 to 900 °C. The dc resistance of the reactor was mainly due to the ohmic resistance of the electrolyte. The transport properties of O^2– through the electrolyte followed Faraday's law under operating conditions. These results were strongly dependent on the morphology and thickness of the palladium electrode.