Investigating Effects of Operational Parameters on the Rate of Electrochemical Cleaning of Chromium Deposits on Strontium-Doped Lanthanum Manganite Cathodes in Solid Oxide Fuel Cells

Abstract

Chromium poisoning of the cathode remains a significant obstacle to the long-term performance of solid oxide fuel cells. Previously, a quick, easy method was introduced that requires no material modifications, major thermal cycling, nor exposes the cell to any species it does not already encounter during operation. The method, electrochemical cleaning, reverses the electrochemical deposition reaction of chromium-containing species by applying a mild anodic bias. Chromium vapor species are formed, freeing active sites in the cathode. The method has been shown to completely recover cell performance via this current-voltage technique.The present work investigates the mechanism of electrochemical cleaning by assessing the effect of various operating parameters on the rate of chromium removal. Using a design of experiments method, eight cells were poisoned and then cleaned using differing combinations of the following cleaning parameters: cell temperature, air humidity, anodic current density, and fuel humidity. Regression analysis of two comparative metrics, cell performance via current voltage curves and post-test chromium content determined via Energy Dispersive Spectroscopy, demonstrated that cell temperature has the highest effect on the rate of chromium removal, followed by air humidity. A refined parameter space for future study is proposed for further optimization of the parameters. Previously, the electrochemical cleaning method was shown to be effective in the removal of Cr2O3 deposited species, but not Cr-Mn spinel deposits. The effects of operating parameters on the removal of the two different types of Cr deposits is discussed. An additional process for the removal of Cr-Mn spinel is demonstrated, which again makes use of the cell operating parameters. Together, the two methods present a facile, periodic process to greatly extend solid oxide fuel cell lifetime.