Performance of SOFC coupled with n-C4H10 autothermal reformer: Carbon deposition and development of anode structure

Abstract

The performance deterioration of solid oxide fuel cells (SOFCs Nickel Yttria stabilized zirconia (Ni YSZ)/YSZ/lanthanum doped strontium manganite YSZ (LSM-YSZ)) coupled with n-C4H10 steam reformers (SR) autothermal reformers (ATR) or catalytic partial oxidation reformers (CPOX) was examined using an integrated system of a micro reactor reformer and SOFC unit The terminal voltage rapidly degraded in CPOX driven SOFC (oxygen to carbon ratio (OCR) = 0 5) while it was fairly stable for SR driven SOFC (steam to carbon ratio (SCR) = 2) over 250 h For ATR driven SOFC at near the thermoneutral point (OCR = 0 5 and steam to carbon ration (SCR) = 1 3) significant deterioration of the terminal voltage was observed in 100 h of operation The main precursors of carbon deposition on the SOFC were identified by reformate gas analysis during the tests In this study we reveal that the carbon deposition on the SOFC anode can be affected by not only lower order hydrocarbons ((C1C4)-C-similar to) but also by the CO/H-2 gas mixture The change in electrical conductivity of the Ni YSZ cermet used for the SOFC anode was investigated under different gas mixtures To investigate the propensity for carbon deposition by each carbon containing gas mixture, we defined the ratios of steam to specific carbon ((C1C4)-C-similar to lower order hydro carbons and CO) in the reformate gas (SSCR steam to specific carbon ratio) To inhibit carbon deposition on SOFC anode, the SSCR must be sufficiently high However the reformer operates near its maximum efficiency at low SSCR value and the higher the SSCR value the lower the open circuit voltage and operating power density due to Nernst potential In this study, a metal foam supported SOFC single cell (Ni YSZ/YSZ/Gd doped ceria (CGO) buffer layer/lanthanum strontium cobalt ferrite-samarium doped ceria (LSCF SDC)) impregnated with catalyst was designed this novel SOFC was then examined for operation at a low SSCR value of the autothermal reformer conditions (near maximum efficiency of n C4H10 reformer and thermal neutral point SSCR = 0 5 OCR = 0 5 and SCR = 1 3) The voltage for the metal foam supported SOFC impregnated with 05 wt% Rh/CGO remained at a nearly constant value around 0 8 V, for 200 h under a constant temperature of 750 degrees C and current load of 250 mA cm(-2) (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved