Modelling Accelerated Ageing and Degradation of Solid Oxide Fuel Cells (MAAD-SOFC)

A major hurdle in the successful commercialization of SOFCs is the degradation of the cell and stack components over long exposures at the high operating temperatures. Lifetime and reliability are two of the most critical issues for the success of SOFC systems. An SOFC system is supposed to run for several thousand hours without significant degradation in the output power. To assess lifetime of an SOFC, long-term tests are needed. Due to the enormous experimental efforts necessary to conduct such measurements with statistical confidence, the development of cells with improved durability is time-consuming and thus expensive. Another challenge is the analysis of the tested cells with respect to the physical failure mechanisms. As the total damage achieved during long-term tests is often low, the dominant degradation process is difficult to identify. In reliability engineering, accelerated life testing (ALT) is a well known method to address these problems. In an ALT, the life data obtained from aggravated test conditions are extrapolated to normal operating conditions by means of a model which fits the data to an appropriate life distribution and uses a life-stress relationship to project the life at normal operating conditions. One of the crucial factors in ALT is that the degradation mechanism should not change on aggravation of the test parameters. Therefore, it is imperative to understand the degradation mechanism SOFCs at the different operating conditions. Though possible, it is very challenging to predict such mechanisms. This necessitates the development of proper models which can predict the degradation mechanism. A model validated with experimental evidences can serve as a useful tool to understand the degradation mechanism of SOFCs and hence will help designing SOFCs with required degradation rate to sustain the operation challenges. The major factors which influence the degradation of SOFCs are temperature, thermal cycling, redox, load cycling and poisoning effects from fuel contaminants such as sulphur and carbon. Therefore, the effect of these factors will also have to be studied and integrated with ALT studies. The understanding gained on degradation from these experiments and the developed model can be utilized to develop new materials which can perform at the same level but at lower temperatures and also have better redox and poison (sulphur/carbon) tolerance.

Economic impact
It is a well known fact there are several barriers into fuel cell technology. To reiterate, low cost, durable and fuel flexible SOFC are required in order push this technology towards commercialisation. It is envisaged that through this project a route commercialisation of SOFC-CHP can be highlighted. The potential impact in the UK is massive. The challenge is to meet rising energy demands whilst moving to a low carbon economy. To help tackle global warming, the UK is putting itself on a path to cut its carbon dioxide emissions by 80% by 2050, with real progress by 2020 [1,2]. This commitment will require carbon reductions to be made by all industries including the housing/industrial building sector [3]. Carbon dioxide emissions from this sector have risen by more than 5% since 1997 and account for 27% of the UK's carbon footprint [1]. According to the World Business Council for Sustainable Development, buildings consume 40% of the world's primary energy, making it the most energy-hungry sector [4]. Studies conducted by the international energy agency have shown that with more efficient production and use of energy, it could be the single largest and most cost-effective contributor to reductions in CO2 emissions. The adoption of CHP, which utilises the thermal energy that is normally wasted, can significantly improve energy supply efficiency. At present up to 70% of available energy is lost at the power station [5]. The UK government has highlighted the building industry as a key sector where carbon reductions can be made. As a result there is increasing pressure to provide sustainable as well as affordable housing whilst increasing production rates to 240,000 units per year by 2016 [6]. In December 2006, the UK government published the Code for Sustainable Homes (CSH) as a pathway to achieving zero carbon homes in England [7]. The CSH sets ambitious targets for the house building industry, for which the commercial benefits and costs are still unknown. This will also have a big impact in India were energy security and availability is limited and well help the country develop further. The results and models from this project will be protected and shared between the partners either in a spin out company, which could then be utilised in achieving a durable SOFC CHP or licensed to any manufacturer such as Rolls Royce or as a route form an industrial partner to support a future project.

Knowledge generation
The current literature and methods available to understand the degradation issues of SOFCs are not enough to achieve the goal of long term stability and reliability. The results generated through this work will enrich the current understanding. This will help in developing methods to predict the degradation of SOFCs under different operating conditions. One of the key objectives of the project is to develop alternative materials which can better withstand the operating conditions and reduce degradation and drive down costs. The scientific understanding gained from such a study will create a knowledge base on materials better suited for SOFC applications.