Applied Energy, 13 February 2015.
Faculty of Science and Technology, Athabasca University , University Drive, Athabasca, AB T9S 3A3, Canada, Telephone: 1-7803944883, Email: [email protected]
In spite of a myriad of efforts by researchers and industry, the durability, reliability and cost of fuel cells still remain major barriers to scaling-up and commercialization. Unless these challenges are fully understood there is little chance of overcoming them. In this critical review, we will revisit advances in theories of flow field designs made over time. Remarkable progress in theory and application of flow field designs has been achieved, which establish a direct and explicit relationship between configurations, structures, flow conditions and performance that can be used to evaluate different design alternatives for structural and flow conditions in fuel cell stacks with respect to performance and predictive capability. We will then analyze the main issues and challenges within the various concepts and criteria of flow field designs and development of theoretical models. For some time, there have been two key barriers facing engineers in the flow field design of fuel cells. One is finding a specific combination for best performance from thousands and thousands of combinations among configurations, structures and flow conditions. Another is to assess how far a fuel cell is from its optimal/given operating conditions and how a flow field design can be improved to meet specific operating ranges. The performance degradation or failure in scaling-up is essentially caused when some channels in a cell or some cells in a stack deviate from their design conditions due to an uneven gas intake distribution. This deviation can significantly exceed the capacity for water removal and heat diffusion in a channel or a cell, leading eventually to worsening issues such as flooding, drying, and hotspots. Therefore, uneven flow distribution is a root cause of low durability and reliability as well as performance degradation. This is why flow field designs are a strategic solution to integrating performance, flow conditions, structure and electrochemical processes. Finally, characteristic parameters have been proposed as design criteria and measures to tackle uneven flow distribution as well as in the critical issues of durability, robustness and reliability. Therefore, flow field designs are a strategic solution and offer greater opportunities to improve the durability and reliability of large scale fuel cell stacks.