Development of Direct Hydrocarbon Solid Oxide Fuel Cell
Mohamed Shahid (Prof. S. Basu)
21st February 2018, Wednesday, 04:30‐05:00 pm (25+5 mins), ChE Seminar hall
Abstract:-
Solid oxide fuel cells (SOFC) are electro-chemical systems developed to produce electricity with fuel sources using hydrogen (H2) and methane (CH4). In conventional SOFC, lanthanum strontium manganite (LSM), nickel oxide (NiO), and yttria stabilized zirconia (YSZ) are used as cathode, anode, and electrolyte, respectively. NiO is an excellent anode for SOFC application because of its high electrochemical activity towards H2 oxidation. But, agglomeration of nickel particles due to sintering is a serious concern at elevated temperatures (800 ˚C) during SOFC testing. In CH4 environment, nickel accelerates coke deposition over its active surface which degrades the performance of SOFC with time at 800 ˚C.
In order to address the above mentioned issues, we have developed doped strontium titanate (SrTiO3) based perovskite anodes. In order to increase the electrical conductivity, lanthanum (La) is doped at A-site of SrTiO3 using solid state route, forming La0.3Sr0.5TiO3-δ (LSTA-). The bilayers, made of LSTA- anode with YSZ, gave a large polarization resistance (Rp) of 62 Ω cm2 with decreased performance in power density of 5 mW cm-2 (20 mA cm-2) at 800 ˚C. We impregnate the bilayer containing LSTA- anode with various fractions of NiO; 2, 4, 6, 8 and 10 wt% to improve the electro-catalytic performance and study the sintering effects of nickel (Ni) in hydrogen (H2) environment. 4 wt % NiO is found optimum and resistant to sintering providing a lesser Rp of 4 Ω cm2 with maximum power density of 32 mW cm-2 (70 mA cm-2). 6 wt% CeO2 in addition to 4 wt % NiO increases the electro-catalytic activity towards H2 oxidation in LSTA- anode containing bilayers. The performance increased by providing a maximum power density of 200 mW cm-2 (500 mA cm-2) with lesser Rp of 0.5 Ω cm2.
Compared to uni-doped anodes of LSTA-, bi-doped perovskite anodes of La0.3Y0.1Sr0.4TiO3+δ (LYSTA-) with lanthanum and yttria doped at A-site of SrTiO3 is better as the bilayer, containing LYSTA- anodes with YSZ, gave a lesser polarization resistance (Rp) of 25 Ω cm2 compared to LSTA- bilayers with Rp of 62 Ω cm2. Impregnated structures with 4 wt% NiO and 6 wt% CeO2 increase the electro-catalytic activity towards H2 oxidation by providing a maximum power density of 170 mW cm-2 (310 mA cm-2) with lesser Rp of 0.9 Ω cm2. Even with CeO2 impregnation, carbon deposition is a serious problem as filamentous carbon deposits were found in 4 wt% NiO and 6 wt% CeO2 impregnated LYSTA- bilayers in humidified CH4 leading to degradation in performance as time progresses, with stay at 800 ˚C. Hence, the bilayers of composite anode containing 4 wt% NiO and 6 wt% CeO2 impregnated LYSTA- anodes with varying fractions of YSZ; 10, 30 and 50 wt % are studied in hydrogen and humidified methane. In particular, bilayer containing composite anode with 30 wt % YSZ demonstrated improved performance by providing lesser activation energy for fuel (hydrogen/methane) oxidation (65.62/104 KJ mole-1 compared to bilayers with composite anode of 10 wt % YSZ (80.38/122 KJ mole-1) and 50 wt % YSZ (78.88/106 KJ mole-1). The study suggests that the presence of YSZ in LYSTA- anode annihilates sintering of Ni and CeO2-x particles in H2 and formation of filamentous carbon in humidified CH4. Percolation studies are carried out to estimate the percolation threshold of YSZ in composite anodes and to quantify the electro-chemical significance of YSZ in composite anodes of LYSTA-.