Redox Stable Solid Oxide Fuel Cells with Ni-YSZ Cermet Anodes Prepared by Polymeric Precursor Infiltration

Abstract

Redox stable SOFCs with Ni-YSZ cermet anodes were developed for electrolyte supported design (electrolyte thickness: 170 μm). Redox stable Ni-YSZ anode was prepared by infiltrating polymeric NiO precursor into pre-sintered porous YSZ layer (∼10 μm thick) followed by reduction ex situ. Polymeric precursor infiltration technique yielded a Ni-YSZ cermet microstructure with nanosized Ni particles coating the surface of porous YSZ. Low temperature processing of nanostructured Ni-YSZ cermet resulted in the reduction of internal stresses between Ni/NiO coating and YSZ skeleton during the redox cycling process. Electrolyte supported SOFC prepared with Ni-infiltrated anode showed a power density of ∼0.315 Watt.cm −2 and a highly redox stable anode (reduction of power density less than 1% after 15 redox cycles) in humidified forming gas (10%H 2 -90%Ar).Solid oxide fuel cells (SOFCs) are promising energy conversion devices due their high efficiency and fuel flexibility. Typical SOFCs use Ni-YSZ cermet as anode and LSM-YSZ composite as cathode with YSZ (Yttria-Stabilized Zirconia) electrolyte. Ni-YSZ cermet is an attractive anode material due to the fact that it provides low ohmic and polarization resistances at operational temperatures (600-1000 • C). Commonly, Ni-YSZ cermet is prepared by co-sintering a mixture of NiO and YSZ powders at high temperatures (1300-1450 • C), followed by ex situ reduction in fuel (e.g. hydrogen) at 800 • C. 1 During long term operation, it is expected that the SOFC will go through several redox (reduction-oxidation) cycles due to intentional or erroneous interruption of fuel supply. 2 Therefore, it is of great importance that the Ni-YSZ cermet withstands several redox cycles in order for SOFCs to be viable for long term operation. However, the initial performance of the fuel cell is generally not recovered after redox cycling due to the mechanical failure of Ni-YSZ cermet. The internal stresses caused by the expansion of Ni upon oxidation crack the YSZ in the cermet structure. 3-5 This causes a severe degradation in performance and even destruction of the electrolyte in configurations with thin electrolytes. 6,7 One of the approaches to obtain redox stable anodes is replacing Ni with ceramic materials that are redox stable by nature and electronically conductive in reducing atmospheres. 7-11 On the other hand, significant effort was focused on the understanding of the redox behavior of Ni/NiO and the modification of the standard Ni-YSZ cermet accordingly. These modifications include the variation of Ni content and grain size, introduction of a buffering interlayer, using 3 mol% YSZ for improved mechanical strength and addition of dopants to the structure. 4,5,[12][13][14] Considering the fact that the degradation of Ni-YSZ cermet processed at temperatures above 1300 • C is caused by mechanical stresses associated with the Ni phase, low temperature processing techniques, such as infiltration into pre-sintered porous YSZ skeleton was proposed. 15,16 It was reported that the conductivity of the Ni...

A Review of RedOx Cycling of Solid Oxide Fuel Cells Anode

“…The cell showed an activation upon the first 15 RedOx cycles at 800 °C, going from 0.8 to 1.5 A cm −2 at short circuit [210]. …”

“…with NiO on GDC–0, U at 0.2 A/cm 2 30 min under air, 30 min under propane510.12Barnett et al . [249]Porous YSZ impregnated with Ni on 8YSZ–+5.8, i at short circuit (0 V)800 °C, air, 15 min151–Buyukaksoy et al [210]Ni-CGO0+2.2, ASR 0.9–0.75 V900 °C, air during 10 h115 SRU100Sfeir et al [163]Ni-CGO on ScSZ–+2.3, ASR 0.9–0.75 V900 °C, fuel gas off until full oxidation155 SRU100Mai et al [164]Graded Ni-20SDC on stabilized zirconia–+1, R p anode−3.2, R s anode850 °C, fuel gas decrease to zero, driving current15 SRU–Batawi et al [132]Ni-CGO on 3Y-TZP–−0.14, U at 0.188 A/cm 2 850 °C, fuel gas off and cool down in 4 h8330 SRU127.8Brabandt et al [166]Ni-CGO on 3Y-TZP–−1.0, U at 0.17...…”

Performances of Plasma Sprayed Metal‐supported Solid Oxide Fuel Cell and Stack

“…This developed single cell stack is able to deliver the remarkable power densities of 39 W (481 mW cm -2 ) and 27.4 W (338 mW cm -2 ) at 750°C and 700°C. The developed stack with 25 such MS-SOFCs can also deliver a remarkable output power of 829.8 W at 39% fuel utilization, 19.85 V and 740°C. Each cell in this 25-cell MS-SOFC stack has an OCV value larger than 1.05 V, showing the gas tightness of the electrolyte.…”

Redox Stable Anodes for Solid Oxide Fuel Cells

“…This may be attributed to simultaneous reduction and sintering of Ni (Sarantaridis and Atkinson, 2007). On the other hand, significant volume increase after re-oxidation was observed by Cassidy et al (1996) compared to the initial state. The authors explained that the large volume change upon re-oxidation followed by the simultaneous reduction and sintering for Ni might exceed the accommodation provided by the porosity.…”