Bin Hua

BaZr0.1Ce0.7Y0.1Yb0.1O3−δ enhanced coking-free on-cell reforming for direct-methane solid oxide fuel cells

A novel anode with a Ni0.5Cu0.5Fe2O4 (NCFO)–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) composite on NiO–Y2O3 stabilized ZrO2 (YSZ) is fabricated and investigated in dry and wet (3 mol% H2O) CH4 at temperatures ranging from 650 to 800 °C. For comparison, a conventional NiO–YSZ anode is also prepared. In H2–3 mol% H2O at 600 °C for 2 h, NCFO and NiO are fully reduced to Ni–Cu–Fe alloys (NCF) and Ni, respectively, forming bi-layer NCF–BZCYYb/Ni–YSZ (BL) and single-layer Ni–YSZ (SL) anodes. The polarization resistance of the BL anode in dry and wet CH4 is only approximately 1/5 of that of the SL anode due to the enhancement of NCF–BZCYYb on CH4 oxidation. This improvement is also supported by the results from DC polarization. Carbon deposition is inhibited in the BL anode by adding only 3 mol% H2O into dry CH4 and the carbon formed in dry CH4 can be removed by subsequent exposure of the BL anode to wet CH4. The overall electrochemical performance of the BL anode is significantly stable in wet CH4, which suggests that it is promising for applications in direct CH4 solid oxide fuel cells (SOFCs).

Enhanced electrochemical performance and carbon deposition resistance of Ni–YSZ anode of solid oxide fuel cells by in situ formed Ni–MnO layer for CH4 on-cell reforming

Two types of anode were prepared for a comparative study of their electrochemical performance and carbon deposition resistance. The first one was the Ni–YSZ cermet anode; and the other, designated as the Ni–MnO/Ni–YSZ, was the Ni–YSZ anode plus an on-cell reforming layer of Ni–MnO in situ reduced from MnNi2O4 with a microstructure of fine Ni particles embedded in MnO matrix. With the Ni–MnO layer on the top surface, open circuit polarization resistance of the Ni–YSZ anode decreased approximately by 1/2 in H2-3 mol% H2O and by more than 1/3 in CH4-3 mol% H2O at temperatures ranging from 650 to 800 °C. Carbon fibers were observed in the Ni–YSZ anode, rather than in the Ni–MnO/Ni–YSZ anode, after initial impedance measurements in CH4-3 mol% H2O for 1 h. The polarization resistance of both anodes at 800 °C increased with time up to 6 h in CH4-3 mol% H2O due to carbon deposition; however, the carbon formed in the Ni–MnO/Ni–YSZ anode had a lower degree of graphitization. In the atmosphere of CH4-20 mol% H2O, carbon deposition was completely depressed in the Ni–MnO/Ni–YSZ anode at 800 °C and 200 mA cm−2, which ensured a higher and more stable electrochemical performance than that of the Ni–YSZ anode.

Oxidation Behavior and Electrical Property of a Ni-Based Alloy in SOFC Anode Environment

The oxidation behavior and electrical property of a Ni-Mo-Cr alloy at 750°C in a simulated solid oxide fuel cell (SOFC) anode environment (humidified and diluted H 2 ) have been studied. The thermally grown oxide scale presents a multilayered structure, which is similar to that formed in air, with densely grown Cr 2 O 3 in between an underneath layer of the intermetallic compound MoNi 3 and a less compact top layer consisting of MnCr 2 O 4 with Cr 2 O 3 flakes embedded. The oxidation kinetics obey a two-stage parabolic law with an initially fast oxidation (0-170 h at a rate of 4.94 X 10 -14 g 2 cm -4 s -1 ) followed by a slower steady oxidation (170-1000 h at a rate of 2.84 × 10 -14 g 2 cm -4 s -1 ). The H 2 /H 2 O reducing atmosphere, even with a significantly lower oxygen partial pressure, has a negative effect on the high temperature oxidation resistance; however, it enhances the adherence of the scale to the substrate. The outward diffusion of Ti ions changes the composition, lattice parameters, and diffraction peak positions of the formed oxides, leading to Ti-doped Cr 2 O 3 and the MnCr 2 O 4 spinel. The area specific resistance of the oxide scale preformed at 750°C for 1000 h is 8.34 mΩ cm 2 at 750°C, which is higher than that formed in air and lower than that of other studied Ni-based alloys.