Eletrodeposição de cobalto em aço inox ferrítico AISI 430 estabilizado ao nióbio: aplicação como interconector de pilhas a combustível de óxido sólido

Abstract

Solid oxide fuel cells (PaCOS) are devices capable of converting chemical energy into electrical energy with high efficiency and low pollution. They are composed of several unit cells (anode, electrolyte, cathode) connected in series by the interconnectors that have the dual function of promoting the electrical contact and making the distribution of the gases between two adjacent unit cells. Of all the components of the PaCOS, the interconnectors are subject to the most severe conditions during the period of operation and therefore must meet the most stringent requirements for their proper functioning. The metallic interconnectors have several advantages such as low cost, high thermal and electrical conductivity, good mechanical resistance and ease of manufacture. Ferritic stainless steels are the most promising materials for this application, however they may undergo oxidation during the operation of the PaCOS, whose temperatures are between 600 and 1000ºC. The volatilization of chromium causing cathode poisoning is another impediment to the use of these materials as an interconnector. One possible solution to these problems is the application of protective coatings. The objective of this work is to obtain dense and uniform films of cobalt oxide on the AISI 430 ferritic stainless steel stabilized to the niobium using three techniques of electrodeposition: potentiostatic, galvanostatic and pulsed current. After deposition all the samples were subjected to a heat treatment of 100 hours at 800ºC in air simulating the conditions of operation of the cathode side cell. The obtained films were characterized by X-ray diffraction to verify the formation of the cobalt oxide layer. In these samples, area specific resistance (ASR) was measured during oxidation in air at 800 ° C for 24 hours using the two-wire four-wire DC method. From these data some samples were selected to be characterized by Scanning Electron Microscopy and Dispersive Energy Spectroscopy. An oxidation test at 800ºC in air per 1,000 hours was also carried out to evaluate the mass gain.