Studying the CO-CO_2 characteristics of SOFC anodes by means of patterned Ni anodes

摘要

The high potential of solid oxide fuel cells (SOFC) arises due to the high degree of efficiency and fuel flexibility. However, the elementary kinetic steps of the anodic processes taking place at the boundary of electrolyte-anode-gas are still largely unknown. Patterned Ni anodes on Y_2O_3-stabilized ZrO_2 are regarded as a promising method to determine these kinetics. In analogy to our previous study with patterned Ni anodes for the H_2-H_2O system, this study is systematically devoted to the elementary kinetics of the CO electrochemical oxidation in CO-CO_2 gas mixtures. Data analysis is backed by extensive knowledge on patterned anode stability and dynamics gained during previous studies. The electrochemical characterization is performed for a large parameter variation range (pCO_2, pCO and T) by electrochemical impedance spectroscopy. Contrary to the characterization in H2-H2O atmosphere no slow relaxation processes were observed and the degradation rate is smaller. Changes in parameter dependency over the investigated parameter range indicate different reaction mechanisms as a function of gas composition. Only slightly higher polarization losses are observed for CO oxidation compared to H2. The comparison of the results from patterned anodes to high-performance Ni/8YSZ cermet anodes employed in anode supported cells yields good agreement.