No abstract

The stability of tubular metal supported SOFC has been studied as a function of current load, thermal cycles and interconnect-sealing concepts. Long term testing under applied current at 800ºC have been performed over 1000 hours on standard cells. Thermal cycles have been proven intensely (250 cycles) during over 700 hours. Major cause for degradation has been identified in terms of the anode interconnect-sealing design, which involves specific handling and machining of tubes and generation of initial submicron cracks. Cell microstructure seems stable after 1000 hours testing at 300 mA/cm2 and 800ºC.

Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. Latest achievements include average cell performances of 400 mW/cm2 at 0.7 V and 800ºC, over 350 thermal cycles and more than 1500 hours of steady operation. Several stack concepts are currently being tested and BoP components such as fuel processing, power electronics and control system developed in parallel to achieve a successful micro-CHP proof of concept by the end of 2010.

Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. The most significant results to date include successful thermal cycling of the cell and anodic connection during 450 cycles and 2000 hours, oxidation testing of the metal support for more than 2500 hours and a comparison of influence of porosity during 100 hours oxidation of metal porous substrates under high water vapour atmospheres.

The aim of this project was to study whether the oxidation resistance of cells is affected while working under high fuel utilization. A previous study measured the weak oxidation resistance for very porous samples (measured porosity ∼ 70%) in H2 with high H2O content (over 50%) in the interval from 600 to 800 °C. Thus, additional tests were carried out with cells. Crofer22APU-supported solid oxide fuel cells (SOFCs) were produced by scalable cost competitive routes. One of the highly porous cells (calculated porosity 45%) was run under high fuel utilization conditions (calculated fuel utilization 56%), and a further two in H2-50%H2O. Another cell, with low porosity (calculated porosity 20%), was kept working in the same H2-50%H2O atmosphere for many hours. Durability tests with cells of different porosities confirmed that this is the main variable concerning degradation issues while working under high fuel utilization.